An Unexpected Diagnosis of Second Primary Malignancy in a Breast Cancer Survivor: A Case Report

Background: Breast cancer survival rates are increasing more than ever with the development of better diagnostic and therapeutic techniques. Survivors of breast cancer have an increased risk of developing second primary malignancies, which may be mistaken for breast cancer recurrence and lead to delayed diagnosis and poor prognosis. Case report: We report a case of a 62-year-old female who presented with shortness of breath and bone pain. She had a history of left triple-positive invasive ductal carcinoma (T1N0M0) treated with bilateral skin-sparing mastectomy, adjuvant Taxotere, and trastuzumab-based therapy and then continued on trastuzumab and letrozole. She underwent imaging to explore the source of her symptoms at which new pulmonary nodules were discovered. During workup, she was found to have elevated tumor markers. They were initially suspected to be breast cancer recurrence metastases based on elevated tumor markers; however, further investigations confirmed that the nodules were a second primary lung adenocarcinoma with a different molecular profile. The patient had disease progression despite chemotherapy and eventually succumbed to her disease. Conclusion: This case highlights the importance of considering second primary malignancies in breast cancer survivors and utilizing advanced diagnostic modalities to efficiently diagnose such cases.