Development of a Second Primary Lung Cancer Following a Primary Breast Cancer: A Case Series

Breast cancer (BC) accounts for 24.2% of all women's malignant tumors, with rising survival rates due to advancements in chemotherapy and targeted treatments. However, second primary cancers, particularly lung cancer (LC), have become more prevalent, often emerging approximately 10 years after BC treatment. This study presents a case series of 9 women diagnosed with second primary LC following BC, treated at a high-complexity hospital in Colombia between 2014 and 2019. All initial BCs were ductal carcinomas, 7 were triple negative, 1 was human epidermal growth factor receptor 2 positive, and 1 was estrogen and progesterone positive. Each patient had undergone radiation therapy, and 7 had received chemotherapy, increasing their LC risk. The second primary LCs, all adenocarcinomas, were confirmed using immunohistochemical stains for thyroid transcription factor-1 (TTF-1), Napsin A, and estrogen receptor (ER) status. The interval between treatments and LC detection ranged from 1 to 17 years, with 4 cases identified after 10 years and 3 within 1 to 3 years, underscoring the need for prolonged surveillance. Seven LCs were ipsilateral to the BC and radiation site, while 2 were contralateral, highlighting the necessity of monitoring both sides for potential LC development. This case series enhances the local epidemiological understanding, showing that prior radiotherapy for BC and histological analysis are key in characterizing second primary LC patients. The study emphasizes the critical role of accurate histological diagnosis in guiding treatment approaches for lung lesions in BC survivors.