High-risk features and tumor differentiation in retinoblastoma: a retrospective histopathologic study.
Abstract: * Context.--Certain histopathologic risk factors in enucleated eyes are important indicators for adjuvant chemotherapy in patients with retinoblastoma.

Objectives.--To determine the frequency of histopathologic risk factors in a large series of retinoblastomas treated by enucleation on file in the pathology laboratory of a large American eye hospital, assess the relationship between tumor differentiation and age at enucleation, and investigate the frequency of photoreceptor differentiation and the role of retinoma/retinocytoma as retinoblastoma precursor.

Design.--Retrospective histopathologic review of 387 eyes with retinoblastoma treated by enucleation including 297 with no prior treatment.

Results.--Fifty-five of 297 untreated eyes (18.5%) had high-risk features. Retrolaminar optic nerve invasion was present in 31 (10.4%), and 24 (8.1%) had massive uveal invasion (defined as >3 mm in diameter). Of the high-risk eyes, 70.9% had iris neovascularization and 60% had neovascular glaucoma. There was a statistically significant inverse relationship between age at enucleation and the degree of tumor differentiation, evidenced by the presence of rosettes. Tumors in older children tended to be poorly differentiated, while rosettes were often numerous in the tumors of younger infants. In all, 20.4% of tumors contained foci of photoreceptor differentiation, which localized in the base of a predominantly endophytic tumor in about one-fourth. Lack of correlation between photoreceptor differentiation and age at enucleation is consistent with early or prenatal malignant transformation. Both preceding observations provide evidence for the hypothetical role of retinoma as a retinoblastoma precursor.

Conclusions.--Slightly less than 1 in 5 infants with retinoblastoma treated by enucleation at a large American eye hospital would require adjuvant chemotherapy on the basis of existing high-risk histopathologic features. Retinoblastomas become progressively less differentiated with time and may be spawned by precursor retinomas.

(Arch Pathol Lab Med. 2009;133:1203-1209)
Article Type: Report
Subject: Retinoblastoma (Risk factors)
Retinoblastoma (Development and progression)
Cell differentiation (Observations)
Histology, Pathological (Research)
Author: Eagle, Ralph C., Jr.
Pub Date: 08/01/2009
Publication: Name: Archives of Pathology & Laboratory Medicine Publisher: College of American Pathologists Audience: Academic; Professional Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2009 College of American Pathologists ISSN: 1543-2165
Issue: Date: August, 2009 Source Volume: 133 Source Issue: 8
Topic: Event Code: 310 Science & research
Geographic: Geographic Scope: United States Geographic Code: 1USA United States
Accession Number: 230247102
Full Text: Retinoblastoma, the most common primary malignant intraocular tumor of childhood, is a major therapeutic success story in developed countries. Adjuvant chemotherapy is one of the factors responsible for remarkably improved survival of children at risk for metastatic disease. Histopathologic risk factors detected during pathologic examination of enucleated eyes are important indicators for adjuvant chemotherapy. We performed an extensive retrospective review of a large series of eyes enucleated for retinoblastoma at a major American eye hospital with an active ocular oncology service--the Wills Eye Hospital/Institute in Philadelphia, Pennsylvania--during a 22-year period. We sought to evaluate the frequency of high-risk histopathologic features in this group of patients, investigate the effect of age on tumor differentiation, and gather evidence supporting the hypothesis that retinal tumors with photoreceptor differentiation--called retinomas or retinocytomas--are retinoblastoma precursors.

MATERIALS AND METHODS

After receiving institutional review board approval, representative microscopic sections, gross photographs, pathology accession forms, and pathology reports from all enucleated eyes diagnosed as retinoblastoma, on file in the ophthalmic pathology laboratory at the Wills Eye Hospital/Institute were retrieved from laboratory archives. Most of the cases had been evaluated and treated by members of the Wills Ocular Oncology Service between May 1986 and May 2008. All eyes had been "grossed," photographed, and submitted for histopathology by the author. All cases initially had been evaluated and diagnosed by the author, or by another experienced ophthalmic pathologist (V.B. Bernardino Jr, MD).

At least 2 standard pupil-optic nerve sections and a transverse section of the optic nerve head from the surgical margin from each case were retrieved for review. The pupil-optic nerve sections included the central part of the longitudinally sectioned optic nerve head. Representative sections prepared from additional tissue blocks were also retrieved when available. Original specimen accession forms, pathology reports, and gross photographs were also retrieved and reviewed.

Clinical data subject to review were limited to information included on the laboratory accession forms that accompanied the enucleated eyes when they were submitted. During analysis, we did not have access to additional clinical data concerning follow-up, survival, or the results of genetic testing, if performed.

[FIGURE 1 OMITTED]

Demographic and clinical data were culled from the pathology accession sheets and tabulated in an Excel spreadsheet (Microsoft, Redmond, Washington). The latter included the pathology accession number, sex, race if indicated, laterality of eye (right or left eye), age of the patient in months at the time of enucleation, tumor classification listed on the pathology accession form (unilateral sporadic, bilateral sporadic, familial or 13q- syndrome), clinical signs at presentation (eg, leukocoria, strabismus, aseptic cellulitis), and other clinical features that were specified and deemed important. Prior therapy was also recorded.

All microscopic sections were examined retrospectively by the author who assessed a number of standard histopathologic parameters and entered the data in the spreadsheet and documented representative findings photomicrographically. Histopathologic data recorded included tumor growth pattern (diffuse, endophytic, exophytic, combined endophytic-exophytic, or indeterminate), the degree of tumor differentiation (poor, spare rosettes, moderate rosettes, many rosettes, photoreceptor differentiation), and the predominant type of rosettes. High-risk features evaluated included the presence and extent of optic nerve invasion (superficial, prelaminar, reaching the lamina, intralaminar, postlaminar, and reaching the line of surgical transection) and the presence, location, and extent of uveal invasion. The lateral diameter and thickness of uveal invasion was measured and recorded in millimeters. Uveal invasion was classified as massive if it was greater than 3 mm in diameter. The presence of anterior segment involvement, including anterior chamber seeding and infiltration of anterior uveal stroma, also was recorded.

Other histologic features evaluated included the presence or absence of iris neovascularization (NVI) and neovascular glaucoma (NVG), the percentage of tumor necrosis, and the presence of necrosis in other intraocular structures. Particular attention was paid to cases with photoreceptor differentiation (PRD). When PRD was identified, its extent and location was determined (eg, massive, basal location, or within treatment regression scar). Other histologic features recorded included tumor seeding, DNA deposition, stigmata of prior therapy, and miscellaneous features such as the presence of extramedullary hematopoiesis.

Statistical analysis was performed by Chirag Shah, MD, of the Retina Service, Wills Eye Institute, by using Excel (Microsoft) and Stata 9 (StataCorp, College Station, Texas).

RESULTS

The series comprised 387 eyes enucleated for retinoblastoma from 194 male patients (50.13%) and 193 female patients (49.87%). There were 186 right eyes (48.1%) and 201 left eyes (51.9%). A binomial probability test showed that there was no significant difference between the proportion of right and left eyes (P = .48).

The patient's race was specified in 286 cases (73.9%): 47 patients (16.4%) were African American, 10 (3.5%) were Asian, 36 (12.6%) were Hispanic, 190 (66.4%) were white, 2 (0.70%) were of Middle Eastern descent and 1 (0.35%) was Native American.

Of the 387 eyes, 86 (22.2%) had a history of prior treatment, 297 (76.8%) had received no prior treatment, and treatment status was unspecified in 4. Prior treatment modalities included systemic chemotherapy (chemoreduction) in 44 of the 86 treated cases, external beam radiotherapy in 26, and radioactive plaque brachytherapy in 26. Six patients had been treated with multiple radioactive plaques and 4 had been treated with rotating plaques. Nine patients had received subconjunctival carboplatin.

Signs and symptoms at presentation were specified in 271 of the untreated cases: 181 (66.8%) had leukocoria and 33 (12.2%) had strabismus. Six patients (2.2%) presented with aseptic orbital cellulitis. All 6 of the latter eyes had severe neovascular glaucoma that had caused extensive necrosis of both the tumor and other intraocular tissues. Three of the 6 had high-risk features, and all had cataracts or dislocated lenses.

Of the 387 patients, 267 (69.0%) were designated on the pathology accession form as having unilateral sporadic retinoblastomas and 114 (29.5%) were presumed to have germline mutations. Of the patients with germline mutations, 103 (26.6%) had bilateral sporadic tumors, 8 (2.1%) had a family history of retinoblastoma, and 3 (0.8%) had 13q- syndrome. Seven of the 8 familial cases had bilateral tumors. Tumor type was not specified in 6 cases. The group designated as having unilateral sporadic disease on the pathology accession forms included 48 patients who were aged 12 months or younger at the time of enucleation and 17 patients who were aged 6 months or younger. It is quite probable that this group contains some patients with unmanifest germline mutations, since the latter tend to spawn tumors at an earlier age.

The mean age at enucleation of the 297 untreated patients, classified as to type of cases, was determined. The mean age of patients in the unilateral sporadic cases was 29.5 months compared to 14.6 months for all germline cases. An unpaired t test with unequal variances confirmed that the statistical difference between the age at enucleation of untreated germline tumors compared to that of untreated sporadic tumors was highly significant (P < .001). In untreated familial cases, eyes were enucleated at a mean age of 11.3 months and in the 2 cases with 13q- syndrome, at a mean age of 3.7 months.

The degree of tumor differentiation in the 297 untreated cases was assessed: 47 (15.8%) had many rosettes, 32 (10.8%) had moderate rosettes, 41 (13.8%) had sparse rosettes, and 121 tumors (40.7%) were classified as poorly differentiated. Of the untreated cases, 56 (18.9%) had some degree of photoreceptor differentiation.

A nonparametric test for trend across ordered groups was used to evaluate the relationship between age at enucleation and degree of differentiation. Younger age at enucleation was associated with a greater degree of tumor differentiation (P < .001) (Figure 1, A and B). The mean age at enucleation for tumors with many rosettes was 10.4 months; for moderate rosettes, 18.3 months; for sparse rosettes, 20.4 months; and for poorly differentiated tumors, 33.9 months.

The mean age at enucleation for all previously untreated eyes with PRD was 31.8 months. In the eyes with PRD, the age at enucleation seemed to reflect the degree of differentiation of the associated retinoblastoma. In 53.6% of previously untreated eyes with PRD, the associated retinoblastoma was classified as poorly differentiated. The mean age of this group was 32.6 months after 2 older children with diffuse infiltrative tumors were excluded.

The mean age for patients with untreated tumors with PRD and any degree of rosettes was younger (23.0 months). The mean patient age for 18 eyes with extensive PRD was 30.6 months, compared to 25.3 and 26.5 months in eyes with moderate and small foci of PRD, respectively. Neovascularization of the iris was present in 167 of the 387 total cases (43.2%). In all, 102 eyes (26.4%) had NVG, which was classified as florid in 37 cases (9.6%). Of eyes with NVI, 3.4% had early angle closure and 8.3% had open angles. Neovascularization of the iris was more common in eyes that had high-risk features; 70.9% of the latter had NVI and 60% had NVG. In contrast, the incidence of NVI and NVG in the untreated eyes without high-risk features was 34.0% and 22.3%, respectively.

The incidence of high-risk histopathologic features was assessed in the 297 untreated cases. Of these untreated eyes, 115 (38.7%) had some degree of optic nerve invasion. The optic nerve invasion was classified as superficial in 24 eyes (8.1%), anterior to the lamina cribrosa in 34 eyes (11.5%), reaching the anterior margin of the lamina in 8 eyes (2.7%), and intralaminar in 11 eyes (3.7%). Retrolaminar optic nerve invasion was present in 31 of the 297 untreated eyes (10.4%). (Figure 1, C). Tumor involved the surgical margin of the optic nerve in 1 of the 387 eyes.

Of the 297 eyes with no prior treatment, 49 (16.5%) had some degree of uveal invasion. The uveal invasion was classified as massive (defined as >3 mm in diameter) in 24 of these cases (48.9%) (Figure 1, D), which represents 8.1% of all untreated eyes. Eight eyes had infiltration of anterior uveal structures (iris and/or ciliary body). The latter represented 2.7% of the 297 untreated eyes.

Risk factors often occurred together: 16 of 37 previously untreated eyes (43.2%) with retrolaminar invasion also had uveal invasion. In 10 of these 37 eyes (27.0%), the uveal invasion was massive.

Overall, 55 of 297 untreated eyes (18.5%) had high-risk features (Table 1): 8 of the 55 eyes (14.5%) had massive uveal invasion and no optic nerve invasion, 7 (12.7%) had massive uveal invasion combined with prelaminar optic nerve invasion, 10 (18.2%) had both massive uveal invasion and retrolaminar optic nerve invasion, 18 (32.7%) had retrolaminar optic nerve invasion and no uveal invasion, 3 (5.5%) had retrolaminar optic nerve invasion and nonmassive uveal invasion, and 2 (3.6%) had a combination of both prelaminar optic nerve invasion and nonmassive uveal invasion. Eight cases (14.5%) were classified as high-risk on the basis of anterior segment involvement. Of the entire series of 387 treated and untreated eyes, 79 (20.4%) had high-risk histopathologic features.

Tumor growth patterns were assessed in the subsets of untreated eyes with and without optic nerve and uveal invasion. The data are shown in Tables 2 and 3. There was no statistical difference between the proportion of each of the 3 growth pattern categories in eyes with optic nerve invasion compared to that in eyes without optic nerve invasion, or between the proportion of each of the 3 growth pattern categories in eyes with uveal invasion compared to that in eyes without uveal invasion.

Some degree of PRD was found in 79 of 387 eyes (20.4%) (Figure 1, E through H). The PRD was classified as extensive or massive in 19 of the 79 cases (24.1%). The PRD was localized in the base of a predominantly endophytic tumor in 19 of 79 cases (24.1%) (Figure 1, G and H). The basal PRD was considered massive in 9 of 79 cases (11.4%) (Figure 1, H). There was no appreciable difference in the incidence of PRD in germline cases (25 of 114; 21.9%) and unilateral sporadic cases (53 of 297; 17.8%). The incidence of PRD was slightly higher in previously treated cases (22 of 86; 25.6% treated versus 57 of 297; 19.3% untreated). In previously treated eyes, PRD typically was found in an area of posttreatment regression. In 18 of 79 cases (22.8%), PRD was found in an area of regressed tumor consistent with prior treatment (treatment regression scar).

COMMENT

The retrospective review reported here was the basis for a lecture honoring Lorenz E. Zimmerman, MD, at the 2008 annual meeting of the American Academy of Ophthalmology in Atlanta, Georgia. I had several questions in mind when I undertook this extensive retrospective histopathologic review. First, I wanted to determine the frequency of high-risk histopathologic features in a large series of eyes with retinoblastoma. Second, I wished to determine if there was an association between the degree of tumor differentiation and the age of the patient at the time of enucleation. Finally, I sought to evaluate the frequency of photoreceptor differentiation in a large series of retinoblastomas and to look for evidence supporting the hypothesis that lesions consisting entirely of PRD--called retinomas or retinocytomas--are retinoblastoma precursors.

Retinoblastoma is one of the great success stories of pediatric and ocular oncology. Although retinoblastoma was almost universally fatal a century ago, survival now approaches 100% at major centers in developed countries. (1) This remarkable improvement in survival reflects advances in medical education and instrumentation, better access to health care, early detection, and modern treatment modalities including the use of adjunctive chemotherapy in patients at risk for metastatic disease. In many cases, the decision to administer adjunctive chemotherapy rests on certain histopathologic risk factors detected during the pathologic examination of enucleated eyes. Conventional risk factors for metastasis in retinoblastoma include extraocular extension or orbital invasion, massive uveal invasion, invasion of the optic nerve posterior to the lamina cribrosa or to the line of surgical transection, and anterior segment involvement.

My interest in the incidence of high-risk histopathologic features was sparked by my participation in the Histopathology Review Committee of the ARET 0332 study sponsored by the Children's Oncology Group. The ARET 0332 study is entitled "A study of unilateral retinoblastoma with and without histopathologic risk factors and the role of adjuvant chemotherapy." Indications for adjuvant chemotherapy in the ARET 0332 study include massive posterior uveal invasion, retrolaminar optic nerve invasion, and any degree of concomitant optic nerve and posterior uveal invasion. It was my impression that the incidence of certain risk factors might have been overestimated in the literature, and I wished to personally assess the incidence of histopathologic risk factors in a relatively large series of tumors treated and evaluated histopathologically at the Wills Eye Hospital/Institute, which has a large and active ocular oncology service.

Slightly less than 1 in 5 previously untreated eyes (18.5%) undergoing primary enucleation for retinoblastoma at Wills Eye Hospital/Institute between 1986 and 2008 had high-risk histopathologic features that would serve as an indication for adjuvant chemotherapy. Of the entire series of treated and untreated eyes, 20.4% eyes had high-risk features. The spectrum of high-risk features found in the untreated eyes is listed in Table 1. Of the 297 untreated eyes, 10.4% had retrolaminar optic nerve invasion and 8.1% had massive uveal invasion. Ten eyes (3.4%) had both massive uveal invasion and retrolaminar optic nerve invasion. Optic nerve invasion was more common than uveal invasion. Of the untreated eyes, 115 (38.7%) had some degree of optic nerve invasion, while 49 (16.5%) had any degree of uveal invasion. Any degree of concomitant uveal and optic nerve invasion is another indication for adjuvant chemotherapy in the ARET 0332 high-risk histopathology study. Only 2 of the 297 untreated eyes fell in the latter category.

The incidence of high-risk features in this study is relatively similar to that observed recently at 2 major American institutions. Uusitalo and coworkers (2) reported an incidence of 9.3% for massive uveal invasion and 11.6% for retrolaminar optic nerve invasion in a combined series of patients from the Bascom Palmer Eye Institute (Miami, Florida) and University of California at San Francisco. In contrast, the incidence of high-risk features in studies from developing countries is higher: 29% of 232 patients from Chennai, India, as reported by Biswas et al, (3) had retrolaminar optic nerve invasion, while 48% of 224 patients at the Hospital de Pediatrla S.A.M.I.C. "Prof Dr Juan P. Garrahan" in Buenos Aires, Argentina, as reported by Chantada et al, (4) had at least 1 high-risk feature.

The incidence of specific high-risk features reported in the literature is quite variable. Factors contributing to the latter are thought to include the period of time when the eyes that were studied were enucleated, the geographic location of the reporting institution, and variations in the techniques used in histopathologic processing and assessment of the enucleated specimens.

The reported incidence of choroidal invasion ranges from 15.2% to 62%. (5-11) The highest incidence is found in an older study by Redler and Ellsworth, (6) who evaluated serially sectioned eyes. Uveal invasion was more common in older series of cases or studies that included many eyes from underdeveloped countries. (10,11) A prior study from Wills Eye Hospital by Shields et al (9) that studied eyes enucleated between 1974 and 1991 reported a slightly higher incidence of choroidal invasion (23%) compared to that in the current study (16.5%), which included eyes enucleated

between 1986 and 2008.

Reports indicate that 24% to 45% of eyes have any degree of optic nerve invasion, while the incidence of retrolaminar optic nerve invasion ranges from 7% to 30%. (7,8,10-14) The latter incidence averages about 10% or less in most recent series. The 30% incidence reported by Khelfaoui et al (10) in 1996 reflects the referral of many patients with advanced disease from non-European countries to the Institut Curie (Paris, France). Biswas et al (11) speculated that the higher incidence of choroidal and optic nerve infiltration that they found in Asian Indian children could be due to delayed diagnosis or to a difference in the biologic behavior of tumors occurring in the Asian Indian population.

In our series, 43.2% of eyes had NVI and 26.6% had NVG. The percentage of NVI in eyes with retinoblastoma reported in the literature ranges from 30% to 60.7%. (7,8,14-17) As noted above, NVI and NVG were much more common in our cases that had high-risk features.

The relationship between age at enucleation and degree of differentiation was examined because it had been the author's impression that numerous rosettes, particularly Flexner-Wintersteiner rosettes, often are found in eyes enucleated from younger infants. We confirmed that the degree of tumor differentiation is indeed inversely proportional to the age in months when the eye is enucleated and that this relationship is statistically significant. On average, retinoblastomas enucleated from older children tend to be poorly differentiated. A similar relationship between tumor cell differentiation and age at enucleation recently was reported by Madhavan and coworkers. (18) The age at enucleation of eyes with PRD seemed to parallel the degree of differentiation of the associated retinoblastoma.

Photoreceptor differentiation, the most advanced degree of retinal differentiation found in retinoblastoma, was described by Ts'o and colleagues in 1970. (19,20) In 1982, Gallie and coworkers (21) suggested that nonprogressive retinal lesions observed in patients known to carry the retinoblastoma gene, and previously thought to represent examples of spontaneous regression, were benign manifestations of the retinoblastoma gene. They proposed the term retinoma for these lesions. In 1983, Margo and coworkers (22) at the Armed Forces Institute of Pathology (Washington, District of Columbia) reported 6 analogous benign retinal tumors composed entirely of photoreceptor differentiation, which they termed retinocytomas. Gallie's retinomas and Margo's retinocytomas presumably are identical lesions composed entirely of photoreceptor differentiation. In the past, such lesions were thought to represent retinoblastomas that had undergone spontaneous regression because they resemble tumors that have regressed after radiotherapy. Ophthalmoscopic examination typically discloses a mass of translucent tissue resembling "fish flesh" with prominent "cottage cheese" calcification and a surrounding annulus of retinal pigment epithelial atrophy. (23)

Dimaras and coworkers (24) recently have shown that both copies of the retinoblastoma RB1 gene are lost or inactivated in retinoma/retinocytoma. They hypothesize that RB1 inactivation in developing retina induces genomic instability but that senescence can block malignant transformation at the stage of retinoma. Stable retinoma is rarely clinically observed because progressive genomic instability commonly leads to highly proliferative retinoblastoma. Gallie and coworkers (25) previously suggested that retinoma was a precursor of retinoblastoma. Both RB1 alleles are mutated in retinoma but further mutational events are necessary for progression to retinoblastoma.

The suggestion by Gallie and colleagues (25) and Dimaras and colleagues (24) that retinoma/retinocytoma is a precursor of retinoblastoma is compelling because there are well-documented cases of malignant transformation of retinoma/retinocytoma into retinoblastoma. In 1989, my colleagues and I (26) reported the case of a young girl who was found to have a retinal lesion consistent with retinoma/ retinocytoma on a preschool screening examination. The tumor was observed without change for more than 2 years and then grew rapidly. The eye was enucleated 34 months after presentation, and histopathologic examination disclosed a biphasic tumor. The basal portion of the tumor, which had been observed for more than 2 years, was composed entirely of photoreceptor differentiation consistent with retinoma/retinocytoma. The inner, apical portion of the endophytic tumor that had grown was a typical malignant retinoblastoma composed of cuffs and sleeves of viable, poorly differentiated, mitotically active basophilic cells separated by sheets of necrosis.

Dimaras and coworkers (24) reviewed a series of 128 eyes with retinoblastoma on file in the surgical pathology archives of the Eye Bank of Canada (Toronto, Canada) and the Hospital for Sick Children (Toronto, Canada) and found foci of photoreceptor differentiation consistent with residual retinoma (20 of 128; 15.6%) contiguous with retina and retinoblastoma. They interpreted this as evidence of clonal progression from a less advanced to a more advanced neoplasm. I found a slightly greater incidence of PRD (20.4%) in our total series of 387 eyes.

Localization of PRD in the base of a predominantly endophytic retinoblastoma, observed in 19 of 79 cases (24.1%), provides additional evidence for the role of retinoma/retinocytoma as a retinoblastoma precursor. Residual PRD previously had been observed in the basal part of retinoblastoma treatment regression scars in eyes enucleated after treatment with chemoreduction. (27) Photoreceptor differentiation is more common in eyes enucleated after radiotherapy or chemotherapy because the well-differentiated part of the tumor is relatively radioresistant or chemoresistant. (28)

As noted above, for eyes with PRD, the mean age of patients was not younger, as one initially would expect, but tended to parallel the degree of differentiation of the associated retinoblastoma. For eyes with PRD, the mean age of patients was 32.6 months if the associated retinoblastoma was poorly differentiated and 23 months if any rosettes were present. Hypothetically, this seemingly counterintuitive observation actually is consistent with the hypothesis that retinoma/retinocytoma is a precursor of retinoblastoma. One would not expect the presence of PRD to correlate with age at enucleation if malignant transformation occurred very early when the retinoma was small, asymptomatic, or clinically undetectable. We speculate that this transformation to retinoblastoma may occur in utero in many instances. Our study, and the previously reported study of Madhavan and associates, (18) indicate that retinoblastomas become progressively less differentiated with the passage of time as additional mutations accumulate. Why rosettes progressively disappear and foci of photoreceptor differentiation persist in otherwise undifferentiated retinoblastomas is poorly understood. The absence of significant degrees of apoptosis and cellular turnover in these highly differentiated retinal precursor neoplasms is one explanation for the persistence of retinomas after malignant transformation. There is no evidence that retinoblastoma can undergo redifferentiation.

In conclusion, our retrospective histopathologic review of a large series of retinoblastomas, treated by enucleation at a large American eye hospital, showed that slightly less than 1 in five had histopathologic risk factors that currently are indicators for adjuvant chemotherapy. The latter include retrolaminar optic nerve invasion and massive choroidal invasion. Many high-risk eyes had multiple risk factors and iris neovascularization. Rosettes were more common in eyes enucleated from younger patients and tumors became progressively less differentiated with increasing age. About 20% of the retinoblastomas contained foci of photoreceptor differentiation. The latter are thought to be residua of well-differentiated precursor lesions called retinomas.

Accepted for publication April 10, 2009.

References

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(3.) Biswas J, Das D, Krishnakumar S, et al. Histopathologic analysis of 232 eyes with retinoblastoma conducted in an Indian tertiary-care ophthalmic center. J Pediatr Ophthalmol Strabismus. 2003;40(5):265-267.

(4.) Chantada GL, Dunkel IJ, de Davila MT, et al. Retinoblastoma patients with high-risk ocular pathological features: who needs adjuvant therapy? Br J Ophthalmol. 2004;88(8):1069-1073.

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(8.) Messmer EP, Heinrich T, Hopping W. Risk factors for metastases in patients with retinoblastoma. Ophthalmology. 1991;98(2):136-141.

(9.) Shields CL, Shields JA, Baez KA, et al. Choroidal invasion of retinoblastoma: metastatic potential and clinical risk factors. Br J Ophthalmol. 1993;77(9):544-548.

(10.) Khelfaoui F, Validire P, Auperin A, et. al. Histopathologic risk factors in retinoblastoma: a retrospective study of 172 patients treated in a single institution. Cancer. 1996;77(6):1206-1213.

(11.) Biswas J, Das D, Krishnakumar S, Shanmugam MP. Histopathologic analysis of 232 eyes with retinoblastoma conducted in an Indian tertiary-care ophthalmic center. JPediatrOphthalmol Strabismus. 2003;40(5):265-270.

(12.) Magramm I, Abramson DH, Ellsworth RM. Optic nerve involvement in retinoblastoma. Ophthalmology. 1989;96(2):217-222.

(13.) Shields CL, Shields JA, Baez KA, et al. Optic nerve invasion of retinoblastoma: metastatic potential and clinical risk factors. Cancer. 1994;73(3):692-698.

(14.) Walton DS, Grant WM. Retinoblastoma and iris neovascularization. Am J Ophthalmol. 1968;65(4):598-599.

(15.) Yoshizumi MO, Thomas JV, Smith TR. Glaucoma-inducing mechanisms in eyes with retinoblastoma. Arch Ophthalmol. 1978;96(1):105-110.

(16.) Spaulding G. Rubeosis iridis and retinoblastoma and pseudoglioma. Trans Am Ophthalmol Soc. 1978;76:584-609.

(17.) Pe'er J, Neufeld M, Baras M, et. al. Rubeosis iridis in retinoblastoma: histologic findings and the possible role of vascular endothelial growth factor in its induction. Ophthalmology. 1997;104(8):1251-1258.

(18.) Madhavan J, Ganesh A, Roy J, et. al. The relationship between tumor cell differentiation and age at diagnosis in retinoblastoma. J Pediatr Ophthalmol Strabismus. 2008;45(1):22-25.

(19.) Ts'o MO, Zimmerman LE, Fine BS. The nature of retinoblastoma, I: photoreceptor differentiation--a clinical and histopathologic study. Am J Ophthalmol. 1970;69(3):339-349.

(20.) Ts'o MO, Fine BS, Zimmerman LE. The nature of retinoblastoma, II: photoreceptor differentiation--an electron microscopic study. Am J Ophthalmol. 1970;69(3):350-359.

(21.) Gallie BL, Ellsworth RM, Abramson DH, Phillips RA. Retinoma: spontaneous regression of retinoblastoma or benign manifestation of the mutation? Br J Cancer. 1982;45(4):513-521.

(22.) Margo C, Hidayat A, Kopelman J, Zimmerman LE. Retinocytoma: a benign variant of retinoblastoma. Arch Ophthalmol. 1983;101(10):1519-1531.

(23.) Singh AD, Santos CM, Shields CL, et. al. Observations on 17 patients with retinocytoma. Arch Ophthalmol. 2000;118(2):199-205.

(24.) Dimaras H, Khetan V, Halliday W, et al. Loss of RB1 induces non-proliferative retinoma: increasing genomic instability correlates with progression to retinoblastoma. Hum Mol Genet. 2008;17(10):1363-1372.

(25.) Gallie BL, Campbell C, Devlin H, et al. Developmental basis of retinal-specific induction of cancer by RB mutation. Cancer Res. 1999;59(suppl 7): 1731s-1735s.

(26.) Eagle RC Jr, Shields JA, Donoso L, et al. Malignant transformation of spontaneously regressed retinoblastoma, retinoma/retinocytoma variant. Ophthalmology. 1989;96(9):1389-1395.

(27.) Demirci H, Eagle RC Jr, Shields CL, et. al. Histopathologic findings in eyes with retinoblastoma treated only with chemoreduction. Arch Ophthalmol. 2003; 121(8):1125-1131.

(28.) Ts'o MO, Zimmerman LE, Fine BS, et al. A cause of radioresistance in retinoblastoma: photoreceptor differentiation. Trans Am Acad Ophthalmol Otolaryngol. 1970;74(5):959-969.

Ralph C. Eagle Jr, MD

From Ophthalmic Pathology Laboratory, Wills Eye Institute, Philadelphia, Pennsylvania.

The author has no relevant financial interest in the products or companies described in this article.

Reprints: Ralph C. Eagle Jr, MD, Ophthalmic Pathology Laboratory, Suite 1410, Wills Eye Institute, 840 Walnut St, Philadelphia, PA 19107 (e-mail: reagle@willseye.org).
Table 1. Spectrum of High-Risk Features in 55 of 297 Untreated Eyes
With Retinoblastoma

                                        Untreated Eyes,
High-Risk Features                        No. (%) (a)

MUI with no ONI                             8 (14.5)
MUI with non-retrolaminar ONI               7 (12.7)
Combined MUI and retrolaminar ONI          10 (18.2)
Retrolaminar ONI and no UI                 18 (32.7)
Retrolaminar ONI and nonmassive UI          3 (5.5)
Combined nonmassive UI and non-retro-
  laminar ONI                               2 (3.6)
Anterior segment                            8 (14.5)

Abbreviations: MUI, massive uveal invasion; ONI, optic nerve
invasion; UI, uveal invasion.

(a) Percentages based on 55 untreated eyes with high-risk features.

Table 2. Growth Pattern in 297 Untreated Eyes with Retinoblastoma
With and Without Optic Nerve Invasion

                                                Endophytic or
                                          Predominantly Endophytic,
Category                   No. of Cases            No. (%)

Any optic nerve invasion       116                26 (22.4)
No optic nerve invasion        181                52 (28.7)

                                 Exophytic or
                           Predominantly Exophytic,
Category                           No. (%)

Any optic nerve invasion          39 (33.6)
No optic nerve invasion           46 (25.4)

                                  Combined
                           Endophytic-Exophytic or
                               Indeterminate,
Category                           No. (%)

Any optic nerve invasion          48 (41.4)
No optic nerve invasion           74 (40.9)

Table 3. Growth Pattern in 297 Untreated Eyes With Retinoblastoma
With and Without Choroidal Invasion

                                              Endophytic or
                                        Predominantly Endophytic,
Category                 No. of Cases            No. (%)

Any choroidal invasion        49                 8 (16.3)
No choroidal invasion        248                70 (28.1)

                               Exophytic or
                         Predominantly Exophytic,
Category                         No. (%)

Any choroidal invasion          12 (24.5)
No choroidal invasion           72 (28.9)

                                Combined
                         Endophytic-Exophytic or
                             Indeterminate,
Category                         No. (%)

Any choroidal invasion          25 (51.0)
No choroidal invasion           99 (39.8)
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