Abstract PO5-08-05: Breast Cancer in PMS2 related Lynch Syndrome: evidence of a possible association?
Authors: Karki Ujjwal , Rangarajan Tara , Zakalik Dana 
Published: May 2024

Abstract
Background:
Lynch syndrome (LS) is a hereditary cancer predisposition syndrome caused by pathogenic variants (PVs) in mismatch repair genes, MLH1, MSH2, MSH6, and PMS2. LS is associated with increased risk of colorectal, and endometrial cancers but breast cancer risk is uncertain, with some studies suggesting MSH6 and PMS2 PVs may have a higher risk for breast cancer. Our study outlines the incidence and clinical characteristics of breast cancer in PMS2-related LS identified at a large academic center.
Methods:
Patients with PMS2 PVs identified between July 2009 and May 2023 were selected from a database at the Nancy and James Grosfeld Cancer Genetic Center at Beaumont Health. Data on demographics, genetic testing, cancer types, and breast cancer characteristics were retrospectively analyzed.
Results:
A total of 108 patients from 74 families were found to carry a pathogenic or likely pathogenic variant in PMS2, of whom the majority were female (75%) and Caucasian (85%). The median age at genetic testing was 52y (19 to 95y). The most common variant was c.137G &gt; T (p.Ser46Ile), seen in 15 of 74 (20%) families. Forty-seven patients (46%) had a personal history of cancer, with a median age at diagnosis of 58y. Of these forty-seven patients, sixteen (34%) had multiple malignancies, including one patient with six separate cancers. The most common malignancies were breast (19; 40%), colon (16; 34%), followed by uterine cancer (7), pancreas (4), and prostate (3). The median age at breast cancer diagnosis was 53y, with a range of 41-78y. The most common histopathology was invasive ductal carcinoma (54%), followed by DCIS (31%), and invasive lobular carcinoma (15%). The majority of patients had breast tumors with stage 0 or 1 (75%), grade 2 (63%), ER-positive (92%), PR positive (67%), and HER2-negative (88%). One patient had triple-negative breast cancer. Sixty-seven percent of breast cancers were less than two centimeters, and 92% were lymph node-negative. Fifty-nine percent received radiation therapy and 53% received chemotherapy.
Conclusion:
Our study outlines the incidence and clinical characteristics of breast cancer in PMS2-related LS. Breast cancer was the most common malignancy in our cohort of PMS2 PV carriers, accounting for 40% of all cancers, supporting a possible association between PMS2 and breast cancer. The majority of PMS2-related breast cancers were invasive ductal type, early stage, intermediate grade, and hormone receptor-positive. Further studies with larger diverse cohorts of patients with LS are needed to better characterize a possible association in order to provide tailored breast cancer screening and management guidelines for this population.
Citation Format: Ujjwal Karki, Tara Rangarajan, Dana Zakalik. Breast Cancer in PMS2 related Lynch Syndrome: evidence of a possible association? [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-08-05.