Abstract
Occult breast cancer (OBC) is a rare form of breast cancer that is detected due to regional lymph node metastasis in the axilla. The patient was a 77-year-old woman. Twenty-four years previously, she had undergone a breast-conserving surgery and axillary lymph node dissection for left breast cancer. Her chief complaint was a mass in the right axilla. The breast magnetic resonance imaging did not show any findings suggestive of malignancy in the right breast. Therefore, an axillary dissection was performed. The results of the histopathological examination diagnosed the patient as having axillary lymph node metastasis of breast cancer. A total mastectomy of the right breast was performed. The patient was diagnosed with ductal carcinoma in situ (DCIS). She is currently undergoing postoperative endocrine therapy with an aromatase inhibitor. This report also includes a discussion of the treatment of OBC and the literature on lymph node metastasis and surgery for DCIS.