A predominant increase in the APC gene isoform with exon 9a in a case of attenuated familial adenomatous polyposis

A unique case of two somatic APC mutations in an early onset cribriform-morular variant of papillary thyroid carcinoma and overview of the literature

We report a case of a 22-year-old female patient who was diagnosed with a cribriform-morular variant of papillary thyroid carcinoma (CMV-PTC). While at early ages this thyroid cancer variant is highly suggestive for familial adenomatous polyposis (FAP), there was no family history of FAP. In the tumor biallelic, inactivating APC variants were identified. The patient tested negative for germline variants based on analysis of genomic DNA from peripheral blood leukocytes. Somatic mosaicism was excluded by subsequent deep sequencing of leukocyte and normal thyroid DNA using next generation sequencing (NGS). This report presents a rare sporadic case of CMV-PTC, and to the best of our knowledge the first featuring two somatic APC mutations underlying the disease, with an overview of CMV-PTC cases with detected APC and CTNNB1 pathogenic variants from the literature.

Cribriform-morular variant of papillary thyroid carcinoma: clue to early detection of familial adenomatous polyposis-associated colon cancer

The cribriform-morular variant (CMV) of papillary thyroid carcinoma (PTC) is a rare histologic subtype of PTC that shows a combination of growth patterns including cribriform and spindle cell areas. The thyroid cancer with this unique histology was originally reported in patients with familial adenomatous polyposis (FAP), although it was later found in patients without polyposis as well. Because of its rarity, its clinical features are not clear. We reviewed seven patients with CMV-PTC who were found among 4194 patients with PTC in our pathology files between June 1991 and March 2003. The prevalence of CMV was 0.16% among all PTCs. We invited these patients to our hospital so we could obtain a detailed family history and recommend colonoscopic examination and germline APC gene analysis. Two patients without subjective symptoms had polyposis of the colon and colon cancers. Germline APC gene mutations were found in both patients. The father of a patient who refused the invitation was revealed to have undergone surgery for colon polyposis. In the remaining four patients, neither polyposis nor APC gene mutation was found. Common clinical features included a young age (mean 25 years), predominance of females, circumscribed tumors, negative node metastasis, and no recurrence of the thyroid cancer after surgery. Two of the three patients with colon polyposis had bilateral multiple thyroid tumors, whereas the remaining four (without polyposis) had a solitary tumor. The histopathology of CMV in patients with PTC should arouse a suspicion of FAP, especially if there are multiple tumors. This finding can lead to early detection of colon cancer.