The T1799A BRAF mutation is absent in cribriform-morular variant of papillary carcinoma.
Context.--Cribriform-morular variant of papillary thyroid carcinoma
(CMVPTC) is one of the rare types of papillary carcinoma. It has been
associated with familial adenomatous polyposis, though it can also occur
sporadically. The molecular pathogenesis of this tumor is incompletely
understood. It appears that there can be molecular contributions from
the RET/PTC translocations and from mutations in the APC gene and
[beta]-catenin gene, which are both part of the Wnt signaling pathway.
However, one of the most common mutations in papillary carcinoma, the
BRAF mutation, has not been reported in this variant of papillary
Objective.--To investigate the BRAF mutational status in CMVPTC.
Design.--Four cases of CMVPTC (1 associated with familial adenomatous polyposis and the others apparently sporadic) were identified from the files of 3 large centers. Deoxyribonucleic acid was extracted and successfully amplified from each case. The polymerase chain reaction products were sequenced and evaluated for the T1799A BRAF mutation.
Results.--None of the 4 cases harbored the T1799A BRAF mutation (0/4).
Conclusions.--The T1799A BRAF mutation does not appear to play a role in the tumorigenesis of CMVPTC.
(Arch Pathol Lab Med. 2009;133:803-805)
Thyroid cancer (Genetic aspects)
Gene mutations (Research)
Gene mutations (Physiological aspects)
Cellular signal transduction (Research)
Cellular signal transduction (Physiological aspects)
Hoschar, Aaron P.
Seethala, Raja R.
Hunt, Jennifer L.
|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|
|Topic:||Event Code: 310 Science & research|
The cribriform-morular variant of papillary thyroid carcinoma
(CMVPTC) is a rare, morphologically distinct variant of papillary
thyroid carcinoma that occurs in association with familial adenomatous
polyposis, as well as occurring sporadically. These CMVPTC tumors are
generally well-circumscribed or encapsulated nodules, but frequently
have areas of tumor invasion into the capsule. The unique morphology of
CMVPTC is characterized by areas demonstrating a cribriform
architecture, with interspersed solid morules of spindled to squamoid
cells (Figure 1, A and B). The lumina of the cribriform areas typically
do not contain colloid. Areas of papillary, follicular, and trabecular
patterns often occur within the same nodule. Psammoma bodies and large
areas of necrosis are not seen. (1,2)
While the molecular characteristics of conventional papillary thyroid carcinoma have been extensively studied, those of CMVPTC have been less completely characterized. Activating rearrangements of the RET/PTC oncogene are characteristic of conventional papillary thyroid carcinoma, (3) and have been shown to be present in CMVPTC (RET/PTC1 and RET/PTC3). (4) Inactivation of the APC tumor suppressor gene4,5 and mutation of the [beta]-catenin gene (CTNNB1)6, both components of the Wnt signaling pathway, have been demonstrated in CMVPTC. Numerous studies have shown that mutation of BRAF, whose product is a member of the RAF kinase family, is the most common oncogenic genetic derangement in papillary thyroid carcinoma (PTC). By far, the most common BRAF mutation in this setting is the T1799A point mutation resulting in the V600E amino acid substitution. (7) The mutational status of BRAF has not been reported in CMVPTC. This study examined 4 cases of CMVPTC for the presence of BRAF mutations.
MATERIALS AND METHODS
The pathology files of 3 large academic institutions were searched for cases of the cribriform-morular variant of papillary thyroid carcinoma. Formalin-fixed, paraffin-embedded tissue was available from 4 cases with this histologic diagnosis. Six slides from each case were prepared at 5-[mu] thickness, and microdissection of tumor-containing regions from each slide was performed. Extraction of DNA was performed with the WaxFree DNA kit (BioMedomics, Inc, Research Triangle Park, NC) by following the standard protocol. Polymerase chain reaction (PCR) was performed for each case by using 100 ng DNA as a template. The thermocycler was run with an annealing phase temperature of 55[degrees]C. The PCR product was verified via electrophoresis on 2% agarose gel. Sequencing reaction of the PCR product was performed by using separate forward and reverse primers. The sequence of the forward primers were 5'-TCATAATGCTTGCTCTGATAGGA-3' and reverse primers, 5'-GGCCAAAAATTTAATCAGTGGA-3'. The sequencing product was purified by using the ExoSAP-IT kit (USB Corporation No. 78200B, Cleveland, Ohio) with standard protocol. The product was sequenced by using the ABI-310 Genetic Analyzer (GMI, Inc, Ramsey, Minn). The resulting electropherograms for each case were compared with those from positive and negative controls, and the presence or absence of the T1799A BRAF mutation was recorded.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Four cases of CMVPTC were identified. One case concerned a patient with familial adenomatous polyposis, while the other 3 cases concerned patients with no apparent history of the disorder and were considered to be sporadic. The lesions ranged in size from 1 to 3 cm. For each case, DNA was successfully extracted and underwent successful PCR amplification, verified by electrophoresis. The sequencing reaction was successful in each case. All 4 cases of CMVPTC were negative for the T1799A BRAF mutation (0/4) (Figure 2).
The BRAF protein is a serine threonine kinase and member of the RAF kinase family. It functions in the RAS-RAF-MEK-ERK (MAPK) pathway. This pathway serves as a link between extracellular growth signals and nuclear protein activation. When activated, this pathway upregulates cell growth and proliferation. Constitutive activating BRAF mutations uncouple BRAF activation from upstream RAS activity and, by extension, from extracellular signaling. (8) The end result is unregulated activation of this kinase cascade, which leads to cell proliferation and tumorigenesis. (9) Activating mutations of BRAF have been implicated in a wide range of malignancies, most notably melanoma and papillary thyroid carcinoma. (10,11)
Many authors have shown that activating mutations of BRAF are important in PTC but not in follicular or medullary thyroid carcinoma tumorigenesis. (7,11-13) In a recent meta-analysis, the T1799A BRAF mutation was present in 810 (44%) of 1856 cases of PTC. (7) Two points stand out from the numerous studies regarding BRAF and PTC. First, mutations of BRAF and activating mutations of other members of the MAPK pathway (ie, RAS and RET/PTC) seem to be mutually exclusive in the vast majority of cases. (12,14,15) Second, BRAF mutation may confer more aggressive tumor behavior. A number of studies have demonstrated a greater tendency toward extrathyroidal invasion, more advanced stage at presentation, distant metastasis, and worse prognosis among patients with BRAF mutation-positive PTC. (16-19)
BRAF mutational status varies by PTC histologic type. The T1799A BRAF mutation was observed in most cases of tall cell variant PTC (77%) and conventional PTC (60%), with far lower prevalence in follicular variant PTC (12%). (7) T1799A BRAF mutational status has not been reported to date in CMVPTC. We performed the current study to attempt to answer this question. The small sample size reflects the rarity of CMVPTC, as only 4 cases were available from the case files of 3 large institutions. While this study is underpowered, the fact that all 4 cases were negative for the T1799A BRAF mutation suggests that this mutation does not play a major role in the tumorigenesis of CMVPTC. This finding is consistent with the observation that CMVPTC carries a relatively favorable prognosis, (2) has been reported with RET/PTC translocations, and may have alternative molecular pathogenesis through the Wnt pathway, as well.
Accepted for publication August 25, 2008.
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David Schuetze, DO; Aaron P. Hoschar, MD; Raja R. Seethala, MD; Adel Assaad, MD; Xiatong Zhang, MD; Jennifer L. Hunt, MD
From the Department of Anatomic Pathology, Cleveland Clinic, Cleveland, Ohio (Drs Schuetze, Hoschar, Zhang, and Hunt); the Department of Pathology, University of Pittsburgh Medical Center, Pittsburgh, Pa (Dr Seethala); and the Department of Pathology, Virginia Mason Medical Center, Seattle, Wash (Dr Assaad).
The authors have no relevant financial interest in the products or companies described in this article.
This work was presented as a poster presentation at the College of American Pathologists Annual Meeting, Chicago, Ill, September 2007.
Reprints: Jennifer Hunt, MD, Section Head, Surgical Pathology, Department of Anatomic Pathology, L25, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195 (e-mail: email@example.com).
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