Abstract
INTRODUCTION: Occult breast cancer (OBC) is defined as metastatic breast carcinoma without detectable breast lesions on clinical or imaging evaluation. Most cases are diagnosed from axillary lymph node metastasis (ALNM), while presentation from other sites is rare. CASE PRESENTATION: A 49-year-old woman with prior gastric cancer developed a 20-mm scalp mass, which was surgically excised. Pathology and immunohistochemistry confirmed metastatic breast carcinoma (hormone receptor-positive and HER2-negative). No breast or axillary lesions were detected by imaging, including PET-CT scan. She was diagnosed with OBC without ALNM and started endocrine therapy with anastrozole. CONCLUSIONS: We report a rare case of OBC diagnosed based on a solitary scalp metastasis without ALNM. OBC without ALNM appears to favor luminal type and distinct metastatic sites, but further cases are needed to establish treatment strategies.