Other Primary Malignancies in Patients with Breast Cancer Who Undergo Germline Panel Testing

Background: Women with a history of breast cancer (BC) more commonly have a diagnosis of other primary malignancies (OPMs) than the general population. This study sought to evaluate OPMs among patients with BC who underwent germline testing with a hereditary BC gene panel. Methods: The study identified women 18 years of age or older with a history of unilateral BC who underwent multi-gene panel testing between January 2014 and August 2019 at the authors’ institution. Patient, tumor, and treatment factors for BC and OPM diagnoses were collected for descriptive, univariate, and overall survival (OS) analyses. Results: Among 1163 patients, 330 (28.4%) had an OPM. The median follow-up period was 4.1 years from BC diagnosis. Of the 1163 patients, 209 (18%) had a BRCA pathogenic variant (PV), 306 (26.4%) had a non-BRCA PV, and 648 (55.7%) had no PV. Development of an OPM varied according to germline testing result, with an OPM developing for 18.6% (39/209) of the patients with a BRCA PV, 31.8% (204/648) of the patients with no PV, and 28.4% (87/306) of the patients with a non-BRCA PV (p < 0.0001). The most common OPMs were ovarian (n = 60), uterine (n = 44), sarcoma (n = 36), melanoma (n = 27), colorectal (n = 22), and lymphoma (n = 20) malignancies. The 5-year OS was 96%. The patients with an OPM 5 years after BC diagnosis had a shorter OS than those who did not (93.4% vs 97.5%; p = 0.002). Conclusion: More than 25% of women with BC who underwent germline panel testing had an OPM diagnosed during the short-term follow-up period, and the diagnosis of an OPM was associated with reduced OS. These data have implications for counseling BC patients who undergo germline testing regarding future cancer screening.