Rare BRCA1 c.3418_3419insTGACTACT:p.S1140Mfs*18 germline mutation in a family with breast and ovarian cancer

BRCA1 is among one of the most frequently mutated tumor suppressor genes in breast and ovarian cancer. In the present retrospective study, a novel heterozygous germline mutation, BRCA1 c.3418_3419insTGACTACT:p. S1140Mfs*18 (C>CAGTAGTCA), was identified in a family with breast and ovarian cancer via next‑generation and Sanger sequencing analysis and the health status of 18 individuals (three with breast cancer, one with ovarian cancer, one with gastric cancer, one with lung cancer, one with colorectal cancer, three with non‑cancer disease and eight healthy individuals) recruited from the 3201 Hospital of Xi'an Jiaotong University (Hanzhong, China) between September 2023 and January 2025 was examined. The aforementioned mutation occurred in four female patients with breast and ovarian and one healthy individual between September 2023 and January 2025, accounting for 27.78% (5/18) of the enrolled family members and 57.14% (4/7) of the patients with cancer. As of March 2025, the treatment of these patients with BRCA1 c.3418_3419insTGACTACT mutations have demonstrated notable therapeutic effects. In particular, in two patients who underwent neoadjuvant chemotherapy, surgical resection and targeted therapy, no recurrence or metastasis as of March 2025. Age risk was analyzed in the present cohort; the area under the curve was 0.9107 and the P‑value was 0.0078 between patients with cancer and healthy individuals. Age may also be a key factor that affects tumorigenesis in breast and ovarian cancer. In conclusion, BRCA1 c.3418_3419insTGACTACT:p.S1140Mfs*18 (C>CAGTAGTCA) heterozygous germline mutation may affect the occurrence and development of cancer.