What happened, in summary

A 46-year-old man presented with a 4 cm irregular mass in his left breast. Biopsy showed an aggressive lobular-pattern breast cancer that was estrogen- and progesterone-receptor positive. HER2 testing was equivocal by staining but showed no gene amplification.

He underwent a left mastectomy with sentinel lymph-node biopsy. Final pathology confirmed grade 3 pleomorphic/solid invasive lobular carcinoma measuring 4 cm. The sentinel node contained scattered tumor cells. Chemotherapy and radiotherapy followed surgery. At 1-year follow-up, he was disease-free.

Because male breast cancer and several other cancers had occurred in his family, he underwent hereditary cancer testing. This identified a pathogenic PALB2 variant. The result provided a potential inherited-risk explanation for his cancer and was relevant to his relatives. Other family members had not yet undergone testing.