Abstract

Synchronous primary cancers occur in 1.7% of breast cancer cases and metaplastic breast cancer (MBC) occurs in less than 1% of breast cancer cases. We present a previously healthy 66-year-old woman diagnosed with MBC after surgical resection of a presumed cyst. A second primary cancer, multifocal lung adenocarcinoma, was discovered during the staging process for her MBC. Remarkably she had not experienced pulmonary or constitutional symptoms at the time of diagnosis. She received chemotherapy with paclitaxel and carboplatin, followed by immunotherapy with nivolumab. At 24 months of follow-up after her initial diagnosis, she was breast cancer-free with stable pulmonary nodules. This case highlights that rather than assuming multifocal lesions represent metastasis, biopsies should be considered as clinical management could be significantly altered in the presence of a synchronous cancer. Furthermore, platinum-based chemotherapy agents have potential to be considered in the treatment of MBC.