Germline BRCA2 Pathogenic Variant in Primary Breast Cancer of a Down Syndrome Individual

BACKGROUND Down syndrome (DS) is the most common genetic disorder, and individuals with DS are known to have a low risk for solid tumors, including breast cancer. In contrast, Breast Cancer Susceptibility Gene (BRCA) pathogenic variant can cause breast cancer. We report a case of primary breast cancer harboring a BRCA2 pathogenic variant in a 35-year-old woman with DS. CASE REPORT A 35-year-old woman with DS presented with a palpable 2-cm mass in the upper-inner quadrant of the left breast. A biopsy confirmed an invasive ductal carcinoma of the breast. Her clinical diagnosis was cT2, N0, M0, cStageIIA. A left modified radical mastectomy with axillary node dissection was performed. Her final pathological diagnosis was invasive ductal carcinoma (T2, pN1, M0, stageIIB), positive estrogen receptors, negative progesterone receptors, negative human epidermal receptor-2 status. She was started on adjuvant hormonal therapy. Unfortunately, 23 months after the operation, multiple metastases were detected. Testing for a BRCA pathogenic variant was performed, and a BRCA2 pathogenic variant was detected. Olaparib was orally administered, and the levels of tumor markers rapidly declined; however, the levels of the tumor markers started to increase again 5 months after the initiation of olaparib. Subsequently, she developed bilateral carcinomatous lymphangiomatosis and died 59 months after the operation. CONCLUSIONS This report highlights a rare case of primary breast cancer harboring a germline BRCA2 pathogenic variant in an individual with DS. Our study highlights the importance of genetic testing as part of breast cancer management in these patients.