Ovarian Microcystic Stromal Tumors Are Characterized by Alterations in the Beta-Catenin-APC Pathway and May be an Extracolonic Manifestation of Familial Adenomatous Polyposis

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To the Editor:
Ovarian microcystic stromal tumor is a rare neoplasm which in the 2014 World Health Organization Classification is included in the category of ovarian sex cord-stromal tumors as a pure stromal tumor.1 It was originally described in 2009 by 2 of us (J.A.I., R.H.Y.) as an ovarian neoplasm exhibiting a distinctive triad of histologic features with microcysts, solid cellular regions, and hyalinized fibrous stroma (Fig. 1).1 These neoplasms have a characteristic immunophenotype with diffuse positive expression of CD10, WT1, cyclin D1, FOXL2, and steroidogenic factor-1 while inhibin and calretinin are usually negative.1,2 In subsequent studies, we and others have demonstrated that most, but not all, microcystic stromal tumors have point mutations in beta-catenin (CTNNB1) and almost all exhibit diffuse nuclear and cytoplasmic immunoreactivity with beta-catenin even in the absence of CTNNB1 mutations.2–6 For example, in our previous study, heterozygous missense point mutations in exon 3 of CTNNB1 were detected in 8 of 14 cases, all of which exhibited nuclear and cytoplasmic beta-catenin immunoreactivity.2 In another study, CTNNB1 mutation analysis revealed missense point mutations in 4 of 6 cases, 5 of which exhibited nuclear and cytoplasmic beta-catenin immunoreactivity, the other exhibiting cytoplasmic staining.4
Occasional examples of ovarian microcystic stromal tumor have been reported in patients with familial adenomatous polyposis (FAP), an autosomal dominant cancer predisposition syndrome caused by germline mutations in the gene encoding the adenomatous polyposis coli (APC) tumor suppressor. Liu et al7 reported a microcystic stromal tumor in a 23-year-old patient with constitutional 5q deletion syndrome, the deletion encompassing the APC gene. Genomic analysis of the microcystic stromal tumor revealed a point mutation in the remaining APC allele which was predicted to result in abnormal splicing of exon 7. Subsequent clinical investigation revealed multiple gastrointestinal polyps qualifying for a diagnosis of FAP. The authors concluded that microcystic stromal tumor is a rare phenotype of FAP.7 Lee et al8 reported a 40-year-old woman with FAP and an ovarian microcystic stromal tumor. On sequencing the APC gene, a novel somatic mutation in exon 11, with a heterozygous deletion at nucleotide position c.1540delG (p.Ala514 Profs*9) was found. In addition, a case of ovarian steroid cell tumor has been reported in a 47-year-old woman with FAP.9 Molecular analysis confirmed biallelic APC inactivation in the tumor and the authors concluded that ovarian steroid cell tumor may be an extracolonic manifestation of FAP. However, on reviewing the photomicrographs of this case, we feel it is possible that this may represent a microcystic stromal tumor, although an expanded immunohistochemical panel would be required to prove this. In all 3 of these cases, CTNNB1 mutations were not detected.
Given these reports, we undertook a follow-up study to our previously published cohort of ovarian microcystic stromal tumors in this journal and looked for APC mutations in 10 of the 14 cases (paraffin blocks of the other 4 cases were not available); we also looked for CTNNB1 mutations using a different protocol. Tumor DNA was obtained from formalin-fixed paraffin-embedded (FFPE) blocks. DNA obtained from the samples was extracted from cells macrodissected from 10 µm unstained serial tissue sections following pathology mark-up to enrich for tumor and normal areas. DNA was subsequently isolated using the QIAamp DNA FFPE Tissue kit (Qiagen). A standard HaloPlex targeted capture10 (Agilent Technologies, Santa Clara) including the entire locus of the APC gene and exon 3 of CTNNB1 encompassing the hotspot area of the gene was designed to interrogate the presence of mutations in the APC and CTNNB1 genes in parallel in the 10 samples. The sequencing data were generated on the Illumina HiSeq2500 sequencer using the 150 bp paired-end sequencing protocol.
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