A Co-Occurrence of Familial Non-Medullary Thyroid Cancer and Lynch Syndrome

Background: Lynch syndrome (LS) is an autosomal dominant disease caused by germline mutations in mismatch repair genes (MMR), leading to the early manifestation of tumors characterized by microsatellite instability (MSI) in >3 family members across at least 2 generations. MSI is a rare event in thyroid cancer (TC), occurring in up to 2.5% of sporadic cases. There is limited data on germline MMR variants’ role in familial non-medullary thyroid cancer (FNMTC). The goal of this study was to analyze the potential clinical and molecular association between LS and FNMTC. Material and Methods: We performed a cohort study analyzing the demographic, clinical, and pathologic data of 43 kindreds with FNMTC. We performed a high-throughput whole exome sequencing (WES) of peripheral-blood DNA samples of 168 participants (54 affected by FNMTC and 140 unaffected). The GATK pipeline was used in variant analysis. The NIH Institutional Review Board approved the study. Results: The study included 383 family members (104 affected, 279 unaffected) aged 43.5 [7-99] years, with 2-9 members per family affected by FNMTC. FNMTC was more prevalent in women (68.3%) and characterized by a median tumor size of 1 [0.2-5] cm, multifocal growth in 44%, gross extrathyroidal extension in 11.3%, central neck lymph node metastases in 40.3%, lateral neck lymph node metastases in 12.9% of patients, and no distant metastases. Family history screening revealed one family of Caucasian descent meeting the clinical criteria for FNMTC and LS diagnosis with 5 members affected by FNMTC and 8 individuals by Lynch-like tumors (3 with colorectal cancer/colon polyps, 2 with endometrial or ovarian tumors, 1 with kidney cancer, 1 with keratoacanthoma and 1 with unspecified Lynch-like tumors with detailed pathology report unavailable). We performed whole exome sequencing of 10 members from this family (3 affected and 7 unaffected) and remaining 158 study participants and detected exclusively in this family, a heterozygous missense variant rs373226409, in MSH2 gene c2120G>A (pCys707Tyr) in three adults affected by LS-like manifestations and two unaffected children under the age of 18 with clear segregation across three generations. This variant appears to be relatively rare with a minor allele frequency (MAF) of 0.0006 in Caucasians; however, it is more common in the South Asian population at 0.003 MAF. Immunostaining performed on the TC tumor tissue of one of the affected family members revealed intact nuclear expression of MSH2, suggestive of no major effect of the variant on MSH2 expression. Five out of seven in-silico models predicted the variant to be functionally deleterious. Conclusion: The co-occurrence of LS and FNMTC is a rare event, presenting in 2% (1/43) of families in our cohort. A common genetic association between LS and FNMTC has not been identified, and the MSH2 variant observed in this family is unlikely to be an etiologic factor.