The patient was a 56-year-old woman. who was aware of a tumor in her left axilla and consulted a nearby doctor. She was referred to our hospital for a detailed examination. No abnormalities were found in the breast by visual inspection, mammography, or breast ultrasound examination. One 29 mm swollen lymph node was found in the axilla. Fine needle aspiration cytology revealed malignant lymphoma; thus, so axillary lymph node excision biopsy was performed, and a diagnosis of axillary lymph node metastasis of breast cancer was made. However, no abnormalities were found. Based on the information presented above, the patient was diagnosed with occult breast cancer cT0N1M0, Stage ⅡA, and breast preservation plus axillary lymph node dissection up to level Ⅱ was performed. No metastases were found in the dissected lymph nodes. The treatment policy for occult breast cancer has not yet been established. We report this case with a review of the literature.