Abstract
INTRODUCTION: Male occult breast cancers are extremely rare and often difficult to diagnose. With only few cases reported, no established treatment is available. And metastatic spread to the small intestine from a tumor originating outside the peritoneal cavity is rare. However, there is a higher tendency for metastasis to the peritoneal cavity, including the small bowel, in the case of lobular carcinoma of the breast. CASE PRESENTATION: A 72-year-old man who initially presented with complaints of abdominal distention. Computed tomography revealed small bowel stenosis. Post-endoscopic stenosis dilatation, an emergency small bowel resection was performed for small bowel perforation. Postoperative histopathology revealed small bowel metastasis due to mammary gland lobular carcinoma with human epidermal growth factor receptor 2 (3+), estrogen receptor-negative, and progesterone receptor-negative status; the patient was then referred to our hospital. Imaging examinations revealed multiple lymph node metastases in the cervical region, right supraclavicular area, mediastinum, hilar region, and splenic portal. However, no obvious breast lesions or axillary lymph node metastases were identified, leading to a diagnosis of metastatic occult breast cancer. Complete response was achieved with trastuzumab plus pertuzumab plus docetaxel therapy; 30 months after chemotherapy initiation, multiple brain metastases were detected. Thus, 30 Gy whole-brain radiotherapy was performed followed by second-line treatment with trastuzumab emtansine. The patient died 4 years and 8 months after the disease onset, due to the progression of the disease with the new brain metastases. CONCLUSIONS: For male occult breast cancer, it is important to understand the potential metastatic patterns and genetic factors, as well as to utilize comprehensive diagnostic methods for early diagnosis and disease management.