Abstract PO4-11-08: Risk of second malignancies in breast cancer patients. A population-based retrospective cohort study between 2010-2020

Abstract Introduction: Breast cancer survivors live longer due to early detection programs and therapeutic advances. Staging and molecular classification are important for prognosis and treatment. At the same time these patients are at increased risk for second primary cancers. Comprehensive evaluation of second cancer risk among patients treated in recent decade with early detection and prevention programs of other tumors lacking. This study aims to identify, characterize and associate breast cancers with second primary malignancies based on different variables. Methods: We identified 3487 females with a first primary breast cancer between 2010 and 2020 in medical records at University Hospital of A Coruña in Spain. Over a median follow-up of 8 years, one hundred patients (2,9%) develop second cancer. According National Cancer Institute, second primary tumor (SPT) was defined as an invasive primary cancer after a first primary cancer. In our case a breast carcinoma. Second cancer risk was evaluated for all cancers (excluding ipsilateral breast carcinoma) which were diagnosed at least 12 months after primary breast tumor. We analyzed breast cancer subtype, family history and pathogenic genetic variants, tobacco use and second primary tumor type. Results: Several clinical characteristics were evaluated, including breast cancer stage, histological type and subtype. The incidence of breast cancer and SPT was increased with age with peaks in the 60’s and 70’s, respectively. Only 13% had SPT between 40-49 years. Approximately 10 women a year, in our study, developed second cancer. 52% of SPT patients had cancer family history. Pathogenic variant study was carried in 25% of women with SPT, 46% of them no mutation were found, but in 17% was detected a germline BRCA1 deleterious variant. Other pathogenic variants were founded: 4% in BRCA2, and 33% in others genes (CHEK2, MSH2, MSH6, PMS2, CDH1, FANC1 y SMAD4) Regards tobacco use, active smokers were 13% and 12% of women had been smoking years ago. Of these 13 active smokers, 10 develop lung cancer (77%) an 5 of former smokers (42%). Luminal subtype was the most common breast cancer (33% Luminal A, 34% Luminal B Her2 negative, 10% Luminal B Her2 positive, 4% Her2-enriched, 10% Triple negative and 3% carcinoma in situ with estrogen and progesterone expression) and stage I and II were most frequent (80%). The most usual second primary neoplasms were lung, colorectal and pancreatic carcinoma (21%, 17% and 7% respectively), and only 2% contralateral breast cancer, with an average of approximately 4 years between breast cancer and the SPT. In 11% of patients were found more than 2 tumors. At the time of the analysis, 73% of these patients are free of disease. In SPT study population few recurrences were described, 2 relapses of breast cancer and 9 of SPT. The median between breast cancer diagnosis and the SPT diagnosis was 54 months [0,7 – 129]. The median to relapse of breast cancer was 73 months [68 – 77]. The median between SPT diagnosis and relapse was 39,25 months [1 - 134]. STP recurrences were observed in colorectal and lung cancer, mainly. Data on recurrences and mutations were not significative. Conclusion: In our breast cancer population the incidence of second primary tumors is around 3% over a 10 – year period. The diagnosis of the SPT arises several years after breast cancer and generally has a worse prognosis. Elevated risks of second cancer among breast cancer survivors treated in recent decade suggests that heightened surveillance is warranted and continued efforts to reduce second cancers are needed. It is mandatory make an effort and focusing in recommendations and advise about tobacco consumption, healthy lifestyle and adherence to Pap test and stool test in survivors. Citation Format: Guadalupe Rama, Maria-Eva Perez-Lopez, Silvia Antolin Novoa, Cristina Reboredo, Beatriz Alonso, Sofia Silva Diaz, Begoña Graña, Lourdes Calvo, Tomas Garcia-Caballero. Risk of second malignancies in breast cancer patients. A population-based retrospective cohort study between 2010-2020 [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 PO4-11-08.