Brain metastasis with subtype conversion in a patient with male breast cancer: A case report

RATIONALE: Brain metastasis of male breast cancer is extremely rare, and the pathological changes between the primary tumor and the metastatic brain tumor have not been reported. Herein, we report for the first time a case of male breast cancer with metastasis to the parietal lobe with subtype conversion after metastasis. PATIENT CONCERNS: we describe a 45-year-old male patient admitted for an incidentally found brain tumor after a motorcycle accident. The patient had been treated for breast cancer 5 years previously. The primary tumor was an invasive ductal carcinoma classified as pT1N1M0 with hormone receptor positivity (estrogen receptor ++, progesterone receptor +++, human epidermal growth factor receptor-type2 (HER2) +) and was treated with surgery, adjuvant chemotherapy, radiation therapy and endocrine therapy (tamoxifen). DIAGNOSES: Magnetic resonance imaging revealed a well enhanced focal solid tumor in the right parietal lobe (5.0 × 4.2 cm in size), Immunohistochemical staining revealed cerebral metastases of breast cancer with HER2 subtype conversion (estrogen receptor +++, progesterone receptor +++, HER2 −). INTERVENTIONS: The patient was successfully treated with surgery and whole brain irradiation (3 Gy × 10 fractions). OUTCOMES: There was no additional complication after the surgery and the patient transferred to oncology department for chemotherapy. 2 years later, he had gamma knife radiosurgery due to the recurred brain lesion and after that he discontinued the treatment and opted for hospice care. LESSONS: Male breast cancer with metastasis to the brain is an extremely rare condition. Although a few similar cases have been reported, subtype conversion in similar cases has not been reported. Therefore, we report this case of a male patient with brain metastasis of invasive ductal carcinoma with HER2 status conversion after metastasis.