Germline testing of patients with personal history of colorectal polyposis by cancer genetics counseling services

47 Background: National Comprehensive Cancer Network (NCCN) guidelines recommend that individuals with >10 adenomatous polyps, ≥2 hamartomatous polyps, or ≥5 serrated polyps proximal to the sigmoid colon have detailed risk assessment and potential genetic testing to rule out polyposis syndrome. Here, we describe germline testing of patients with a personal history of colorectal polyposis by Cancer Genetics Counseling Services. Methods: This is an IRB-approved retrospective chart-review study. Between 2016 and 2020, 1011 unique genetic counseling visits were conducted. Germline testing was recommended by a certified genetic counselor if medically necessary. All patients with a personal history of colorectal polyposis were identified (N=20) and their germline testing results were summarized. Results: The reasons for referral to the Cancer Genetics Counseling Services were personal history of >10 adenomatous polyps (N=13), personal and family history of colorectal polyposis (N=3), personal history of juvenile colorectal polyps (N=3) or personal history of ≥2 hamartomatous polyps (N=1). The median age is 58 years-old (1-84). Ten (50%) patients were females. Caucasians, African Americans and other ethnic backgrounds represented 80%, 10% and 10% respectively. In our cohort, 6 out of 20 (30%) patients had a pathogenic germline mutation, 5 (25%) patients had variant of unknown significance (VUS) and 9 (45%) patients had negative testing. Among patients with pathogenic germline mutations, 3 patients had a pathogenic APC mutation (APC c.1659G>A, APC c.2802C>A and APC c.1643dupT) and were diagnosed with Familial Adenomatous Polyposis (FAP). One patient had 2 pathogenic MUTYH mutations (MUTYH c.536A>G and MUTYH c.1187G>A) and was diagnosed with One patient had a pathogenic PTEN c.634+5G>A mutation and was diagnosed with PTEN Hamartoma Tumor Syndrome. Among the 3 patients with a personal history of juvenile colorectal polyps, one patient had a CHEK2 c.190G>A mutation while the other two had negative genetic test results. The VUS mutations in our cohort were MRE11A c.826C>T, BLM c.3478T>C, BRCA2 c.2519T>C, CHEK2 p.V395L and CTNNA1 c.392dupT. Conclusions: In our cohort of patients with personal history of colorectal polyposis, the majority of patients (45%) had negative germline testing. An underlying pathogenic germline mutation and VUS were identified in 30% and 25% of the patients, respectively. FAP Syndrome was the most commonly diagnosed hereditary polyposis syndrome with 3 patients found to have APC germline mutations. Other pathogenic mutations were identified in the MUTYH, PTEN and CHEK2 genes. Patients with MUTYH and PTEN mutations were diagnosed with MAP and PTEN Hamartoma Tumor Syndromes respectively.