Nonneoplastic alterations of the mammary epithelium can mimic atypia.
Abstract: Context. -- The pathologist evaluating breast biopsy specimens sometimes encounters nonneoplastic alterations of the mammary epithelium that raise the differential diagnosis of atypia. Because the identification of atypical ductal hyperplasia of the breast has significant clinical implications, it is important to correctly recognize its nonneoplastic morphologic mimics.

Objective. -- To highlight a spectrum of physiologic and treatment-related changes that can occur in the mammary epithelium and to discuss the differential diagnosis with true atypia.

Data Sources. -- A comprehensive review of the published English literature on physiologic and treatment-related changes of the breast epithelium was performed.

Conclusions. -- Among physiologic alterations of the ductal epithelium, luteal-phase changes and secretory changes can sometimes be overinterpreted as atypical. Treatment-related changes, secondary to chemotherapy and radiation, can pose a major diagnostic challenge and their misinterpretation as neoplastic carries major clinical consequences. Familiarity with the morphology of both physiologic and treatment-related alterations of the mammary epithelium is essential to avoid misdiagnosis.
Article Type: Report
Subject: Breast diseases (Diagnosis)
Breast diseases (Physiological aspects)
Breast diseases (Care and treatment)
Biopsy (Usage)
Chemotherapy (Usage)
Cancer (Chemotherapy)
Cancer (Usage)
Author: Murray, Melissa
Pub Date: 05/01/2009
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: May, 2009 Source Volume: 133 Source Issue: 5
Accession Number: 230151993
Full Text: Histologic examination of tissue biopsy specimens remains the cornerstone for the diagnosis of breast diseases and it is essential for the pathologist to be familiar with the spectrum of "normal" histologic alterations of the mammary epithelium. The breast is a hormone-regulated organ and its morphology is greatly affected by reproductive hormones. In addition to physiologic changes, therapeutic interventions, such as chemotherapy and / or radiation, also produce morphologic alterations. As more patients with breast cancer undergo breast conservation therapy and survival after breast cancer treatment increases, pathologists will encounter treatment-related changes of the breast. Knowledge of the histologic spectrum of both physiologic and treatment-induced alterations of the breast is of foremost importance to avoid diagnostic pitfalls. This review highlights some of the nonneoplastic alterations of the mammary epithelium in the differential diagnosis of true atypia.

PHYSIOLOGIC CHANGES

The breast undergoes physiologic changes during puberty, pregnancy and lactation, menopause, and postmenopausal age. Furthermore, the cells of the mature mammary lobules (myoepithelium and luminal/ductal cells) undergo physiologic changes associated with the menstrual cycle.

During the follicular phase of the menstrual cycle, the lobules are relatively small, and the acini are tightly clustered. The specialized intralobular stroma is hypocellular and appears slightly fibrotic. The luminal cells lining the acini are small and polygonal, have pale cytoplasm and dark, round, centrally located nuclei. These cells appear crowded and nearly flattened and the acini show small or collapsed lumina. No mitotic activity occurs in the normal epithelium during this phase. The myoepithelial cells are inconspicuous, often barely discernible on close inspection. As the menstrual cycle progresses, the myoepithelium becomes more apparent and acquires vacuolated cytoplasm. Eosinophilic secretions also begin to appear within the acinar lumen (Figure 1).

In the luteal phase, the lobules appear increased in size compared with the proliferative phase. The specialized intralobular stroma responds to progesterone stimulation by becoming loose and edematous and is infiltrated by lymphocytes. The cytoplasm of the luminal cells usually acquires a distinctive basophilic hue and shows polarized morphology, with basally located nuclei and more prominent apical cytoplasm. The nuclei are enlarged and prominent, with conspicuous nucleoli. The acinar lumina are open and contain secretions. Mitotic figures are frequent in the luminal layer, as well as focal apoptosis (Figure 2). In this phase of the menstrual cycle, the myoepithelial cells also become more prominent and show abundant, vacuolated cytoplasm and small, round, centrally located nuclei. (1, 2) In some instances, the enlarged myoepithelial cells with clear cytoplasm can mimic classical lobular carcinoma in situ, undermining normal luminal epithelium. In this setting, however, the lobules are not expanded and do not show increased cellularity and the acinar lumina are patent and lined by polarized cells, also showing luteal phase changes.

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Presence of mitoses, focal apoptosis, nuclear enlargement, and prominent nucleoli can be worrisome findings on high-power examination. In these cases, the diffuse nature of the epithelial changes, the prominent edema of the intralobular stroma, and the finding of a continuous layer of vacuolated myoepithelial cells are useful clues to the diagnosis. Luteal phase changes mimicking atypia should always be in the differential diagnosis when examining a specimen from young to premenopausal women.

The postmenopausal breast consists for the most part of fibrous and adipose tissue with few scattered residual ducts, acini, and vessels. Atrophy of the glandular component is normal with increasing age and is characterized by loss of the glandular epithelium and increasing thickness of the basement membranes, leading to progressive obliteration of the acini. Cystification of the acini may occur, but it is not considered part of fibrocystic disease. Exogenous hormones reduce the atrophic changes and can result in epithelial hyperplasia, with appreciable mitotic activity. (3)

Secretory (Pregnancy-like) Changes

Secretory (pregnancy-like) changes (SC) can occur in the breast independent of pregnancy status. These secretory changes have also been reported in men taking exogenous estrogen. The etiology of these changes is unknown and association with medications has been suggested.

The lobules with SC resemble those of late pregnancy and lactation, but the alteration is usually limited to only 1 or 2 lobules. The affected acini are dilated and lined by a single layer of cuboidal to columnar cells with abundant pale to clear cytoplasm, finely granular or vacuolated. The nuclei are typically small, round, and darkly stained (Figure 3). Sometimes the nuclei protrude into the gland lumen and impart a hobnail appearance to the cells. The epithelium in the lobules usually consists of 2 cell layers but the myoepithelium is inconspicuous; rarely, hyperplasia can occur and is not worrisome. Secretory material is often present within the distended lumina and can become calcified, resulting in mammographically detectable deposits. No further treatment is necessary if secretory changes are present in a core biopsy specimen and the findings are concordant with the imaging.

[FIGURE 5 OMITTED]

Coexistence of SC and cystic hypersecretory hyperplasia has been reported by Shin and Rosen, (4) and is discussed in the next section.

Cystic Hypersecretory Hyperplasia

Cystic hypersecretory hyperplasia (CHH) is regarded as a benign proliferative lesion. Dilated cysts filled with homogenous, eosinophilic, colloidlike secretions constitute its hallmark feature. The characteristic secretions are usually acellular and often retract from the surrounding epithelium, with a smooth or scalloped margin; they rarely undergo calcification and seldom contain histiocytes. The cysts of CHH are lined by a single layer of flat, cuboidal, or columnar cells with eosinophilic cytoplasm; myoepithelial cells are inconspicuous. The epithelial cells have round to oval, monotonous, and bland nuclei (Figure 4). Necrosis and mitoses are not found in CHH. (5)

The differential diagnosis of CHH includes CHH with atypia and cystic hypersecretory carcinoma in situ (CHCIS), as well as clear cell ductal carcinoma in situ. Some morphologic overlap exists in the spectrum of the cystic hypersecretory lesions of the mammary epithelium. The term cystic hypersecretory hyperplasia applies only to cysts lined by monostratified, cytologically bland epithelial cells with low nuclear to cytoplasmic ratio. Increase in nuclear to cytoplasmic ratio, mitotic figures, nuclear pleomorphism, and/or prominent large nucleoli are features indicative of cytologic atypia. Architectural atypia is typically seen in the form of micropapillary growth. Greater extents of architectural complexity (solid, cribriform, and micropapillary growth) together with cytologic atypia are required for the diagnosis of CH-CIS. The latter may not show the typical colloidlike secretions, and necrosis and mitoses can be seen. In contrast to CH-CIS, clear cell ductal carcinoma in situ is typically solid with associated necrosis, and the cells have clear but nonvacuolated cytoplasm; nuclei are hyperchromatic with clumped chromatin and prominent nucleoli.

Recently, Shin and Rosen (4) showed a close relationship between SC and CHH. The authors reviewed 12 biopsy specimens with SC and found coexisting CHH in 5 (42%). Secretory changes histologically merged with CHH in 4 cases. Four biopsy specimens also showed cytologic atypia, but no carcinoma in situ was identified. (4)

The same authors have also reported a series of 9 cases of SC and/or CHH adjacent to carcinoma in situ (7 CHCIS and 2 low-grade micropapillary ductal carcinomas in situ, 1 of which was associated with invasive ductal carcinoma). In this series, the breast biopsies were performed for calcifications (6 cases), mass (2 cases), and nipple discharge (1 case). Secretory changes merged with CHH in 5 cases and were geographically distinct from it in 3, and 1 case showed SC only. All but 3 cases showed atypia in SC, CHH, or both. Six patients underwent mastectomy (2 bilateral) and 2 underwent excision; 1 patient had incomplete surgical history. The patient with invasive carcinoma had micrometastatic nodal disease, whereas no metastases were found in 4 patients who underwent lymph node staging. None of the patients had evidence of disease on follow-up (range, 10 to 69 months). (6) The authors concluded that complete excision of the lesion is prudent whenever CHH is seen on a core biopsy specimen to rule out the possibility of focal carcinoma. (4, 6)

Clear Cell Change

The descriptive term clear cell change applies to an alteration of the epithelium of the terminal duct lobular unit characterized by cytoplasmic clearing. No specific etiology has been reported for this alteration.

The cells usually have abundant cytoplasm, small dark nuclei, and no nucleoli. The myoepithelial cells are maintained. Clear cell change usually constitutes an incidental finding, limited to a lobule or only part of it, and rarely associates with calcifications (Figure 5, A and B). Clear cell change is easily distinguished from clear cell carcinoma, as the latter is usually more extensive and shows markedly atypical, enlarged, and hyperchromatic nuclei.

Occasionally, it is the myoepithelium that shows a prominent clear cell change, but it can be recognized because of its location between luminal epithelium and basement membrane.

A lobule involved by clear cell changes can mimic atypical lobular hyperplasia or focal lobular carcinoma in situ. The polygonal clear cells, though, are cytologically benign and tightly cohesive, with sharply defined cell borders, and the acinar lumen is typically preserved. Positive membranous immunoreactivity for E-cadherin will decorate the cells with clear changes, but not lobular carcinoma in situ.

TREATMENT-RELATED CHANGES

Estimates had indicated that more than 182 000 new cases of invasive breast cancer and an additional 67 000 cases of carcinoma in situ would require diagnosis and treatment in 2008. (7) In the modern day and age, treatment of breast carcinoma usually consists of breast-conserving therapy (BCT), including tumor excision and radiotherapy of the affected breast to eradicate any residual disease. Studies have demonstrated that the outcome of BCT is comparable to that of mastectomy. (8, 9)

Both radiation and chemotherapy can induce morphologic alterations in the breast epithelium; with the increased survival of patients with breast carcinoma, the pathologist must be familiar with the histologic changes introduced by these therapies. Frequently, patients who undergo prior BCT will require a posttreatment biopsy because of new clinically or radiologically detected lesions within the breast. This is the most common setting in which the pathologist will encounter nonneoplastic epithelial atypia secondary to treatment effect.

Chemotherapy

Cytotoxic chemotherapy primarily affects the carcinoma but it also alters the nonneoplastic breast parenchyma, resulting in subtle changes. Following chemotherapy, the nonneoplastic breast parenchyma undergoes diffuse atrophy, with reduced number of lobules and a decrease in size of those remaining (3, 10) (Figure 6). Lobular atrophy consists of a spectrum of changes ranging from concentric thickening of the basement membrane to almost complete fibrous obliteration and sclerosis of the acini. The residual glands are lined by flattened epithelium, but cytomorphologic alterations may sometimes occur and mimic atypia. The epithelial cells are often enlarged and appear less uniform. The cytoplasm can be vacuolated, granular, clear, or eosinophilic and, occasionally, the degree of vacuolization can mimic that seen in histiocytes. (11, 12) Morphologic alterations in the epithelial cells include nucleomegaly, multinucleation, and prominent nucleoli (10) (Figure 7). Marked epithelial atypia is not a common finding and one should be cautious about interpreting any severe epithelial alteration as secondary to chemotherapy effect in nonneoplastic epithelium. Morphologic comparison with the untreated carcinoma is particularly helpful in this situation.

Radiation

The pathologist is often challenged with the difficult task of evaluating a breast biopsy specimen for a patient who has previously received radiation therapy. Care is necessary to avoid overcalling radiation-induced changes as carcinoma because this will result in mastectomy. On the other hand, underdiagnosis of recurrent carcinoma as radiation-induced changes will delay appropriate treatment of a potentially curable disease.

In the course of radiation for BCT, both neoplastic and nonneoplastic breast tissue receive the same level of exposure. Radiation-induced changes are most apparent in the terminal-duct lobular unit and less pronounced in the larger ducts.3,13,14 The alterations include fibrosis, lobular atrophy, collagenization of the intralobular stroma, and thickening of the basement membrane. The epithelial cells of lobules and terminal ducts show cytologic alterations that can mimic atypia, including increased cell size, large pleomorphic nuclei, and often, prominent but small nucleoli (Figure 8). Irradiated nuclei are sometimes hyperchromatic but most often show uniform chromatin. (15) In radiation changes, the cells with enlarged nuclei are scattered and admixed with benign epithelium. The lobules are atrophic and mitotic activity is absent. Finding of mitotic activity is suggestive of recurrent malignant disease. The myoepithelial cells lining the acini tend to be preserved to a greater extent than the luminal cells and may be relatively prominent (Figure 9).

Occasionally, fibrosis distorts the terminal-duct lobular unit and obscures the myoepithelium. In lobules severely affected by radiation treatment, fibrosis may distort the acini, resulting in a pseudoinfiltrative pattern (13) (Figure 10). Close attention to the presence of myoepithelial cells, atrophic epithelial changes, and lack of proliferative activity help the pathologist to distinguish this pseudoinfiltrative pattern from invasive carcinoma.

Atypical stromal fibroblasts are commonly encountered in irradiated breast (Figure 11). Nonspecific vascular changes, such as intimal and myointimal proliferation of small arteries and arterioles, mural hyalinization, and prominence of capillary endothelial cells have also been described.13,15 Fat necrosis and squamous metaplasia are also frequently encountered in postradiation biopsy specimens (14) (Figure 12).

The aforementioned changes are typically described in breast biopsy specimens obtained long after radiotherapy, but occasionally a breast biopsy specimen is obtained in the course of radiation or shortly after its completion because of suspicious radiologic findings (eg, new or residual calcifications). The epithelial atypia present in early posttreatment tends to be severe and diffusely involves the breast epithelium (Figure 13). Severity and extent of the changes make interpretation of these findings even more challenging. A very important point to remember is that the epithelial changes secondary to radiation do not include mitotic activity. In situ carcinoma persisting after radiation treatment remains largely intact and the morphology of neoplastic cells in lobules or ducts is not substantially different from that of the untreated tumor. (3, 16) Recurrent carcinoma in irradiated breast has a similar nuclear grade as that of the untreated tumor in 84% of cases (16) (Figure 14). Therefore, in cases of suspected recurrent or persistent carcinoma after BCT, comparison of the pretreatment and posttreatment tissue sample is extremely helpful.

Local recurrence tends to appear later in women treated with BCT than in those treated with mastectomy. In one report, for example, the actuarial incidence of local recurrence was 7%, 14%, and 20% at 5, 10, and 20 years, respectively, after BCT.17 Changes secondary to radiation have been seen up to 20 years after treatment. One study showed that the histologic changes induced in the nonneoplastic breast tissue by radiation therapy showed no significant progression or improvement during time intervals as great as 229 months. (13, 14) Therefore, the pathologist needs to be familiar with and watch for radiation-induced changes in the nonneoplastic breast tissue even many years after treatment.

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[FIGURE 12 OMITTED]

When faced with epithelial atypia, which may be post-treatment-related, it is necessary to inquire about possible prior history of BCT; unfortunately, information regarding prior radiation therapy, though extremely important, is not always provided. Careful search for histologic evidence of treatment effect in nonepithelial cells can help suggest a prior breast radiation and avoid the overdiagnosing of epithelial changes as ductal carcinoma in situ, even though stromal fibrosis alone has been shown to be a poor correlate of evidence of treatment-related changes when compared with biopsy specimens from nontreated patients.

[FIGURE 13 OMITTED]

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SUMMARY

The histomorphology of the breast parenchyma varies with age and is under hormonal influence. Knowledge of the physiologic changes that occur in the breast is essential to distinguish them from pathologic alterations. Treatment-related changes secondary to chemotherapy and/or radiation may pose a major diagnostic challenge and their misdiagnosis as neoplastic has serious clinical consequences. Because of the success of BCT, pathologists will see increasing numbers of postradiation and/or chemotherapy biopsy specimens. Familiarity with the morphologic alterations of the breast epithelium secondary to treatment effect is thus extremely important to avoid misdiagnosis of treatment-induced nonneoplastic changes, which can persist many years after treatment.

Accepted for publication January 8, 2009.

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Melissa Murraym, DO

From the Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York.

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

Presented in part at the Surgical Pathology of Neoplastic Diseases course, Memorial Sloan-Kettering Cancer Center, NewYork, NewYork, May 12-16, 2008.

Reprints: Melissa Murray, DO, Department of Pathology, Memorial Sloan-Kettering Cancer Center, 1275 York Ave, New York, NY 10065 (e-mail: murraym@mskcc.org).
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