Breast cancer phenotypes in carriers of pathogenic POT1 variants.

Germline pathogenic variants (PVs) in POT1, one of the shelterin complex genes, correlate with tumor predisposition, primarily with melanoma, hematologic malignancies, sarcoma, papillary thyroid carcinoma and glioma. Breast cancer (BC) risk has not been shown to be elevated. We analyzed BC occurrence and features in a cohort of 29 female PV heterozygotes, of whom 13/29 (45%) were diagnosed with BC. Data regarding genetic, clinical, pathologic, treatment, and outcome characteristics were extracted. Patients in our cohort harbored three different POT1 PVs; The c.233T > C Ashkenazi founder PV occurred in 11/13 (84.6%). Median age at first BC diagnosis was 54 years (range 44-72); no patient was diagnosed before the age of 40. Pathological subtypes varied; invasive ductal carcinoma was the most common. All primary tumors were estrogen receptor positive; one was HER2-enriched; no triple-negative cancers were observed. Stage at diagnosis varied: 6 of 10 tumors with known staging were stage 0 or I, and one patient presented with metastatic disease. Treatment approaches were diverse as clinically appropriate. After a median follow-up of 110 months, three second BC events occurred, with no BC-related mortality. Personal and family history of other malignancies were frequent. This is the first dedicated report describing BC phenotypes in POT1 PV heterozygotes. Our findings suggest that enhanced BC surveillance may be warranted in this population. Larger cohorts are needed to further characterize the clinicopathological features of BC in POT1 carriers, to define lifetime BC risk and determine whether BC-specific screening recommendations should be established for this group.