A rare case of lung adenocarcinoma with metastases to the breasts bilaterally

We present a case of a 65-year-old female with a history of stage IV adenocarcinoma of the lung that metastasized to the bilateral breasts. The breasts are a rare metastatic site for lung adenocarcinoma, with metastases to the breasts bilaterally being further unique. Our patient was diagnosed with stage IV adenocarcinoma of the lung with EGFR exon 20 insertion with metastases to the bone and skin four years prior to presentation, and she underwent a left lower lobotomy and multiple failed therapies. Biopsy of her breast masses revealed TTF (lung marker) positive GATA binding protein 3, GCDFP15, and mammaglobin (breast markers) negative metastatic moderately differentiated adenocarcinoma. Next-generation sequencing studies revealed exon 20 mutation, for which there are few effective targeted therapies. She was considered for therapy with amivantamab but ultimately never received therapy due to multiple hospitalizations, and passed away due to septic shock, likely from empyema versus ESBL E. coli urinary tract infection.