Axillary mass suspected to be occult breast carcinoma: a case study of skipped axillary lymph node metastasis from endometrial carcinoma in which core-needle biopsy was useful for diagnosis

A 55-year-old Japanese woman presented with metrorrhagia and was diagnosed with endometrial carcinoma. Chest computed tomography (CT), ultrasonography (US) and magnetic resonance imaging (MRI) showed a left axillary mass. Regarding the diagnosis of the axillary mass, lymph node metastasis from the uterus was first suspected. Metastasis from the breast, lung, thyroid or stomach was considered next. On a general search including positron emission tomography (PET)-CT, there was no abnormality except endometrial carcinoma and the left axillary mass. Skipped axillary lymph node metastasis of endometrial carcinoma is extremely rare, with a reported incidence of 0.03% of endometrial carcinoma cases. The differential diagnosis was double carcinoma of the uterus and breast. We carried out US-guided core needle biopsy (CNB) of the axillary mass, and the histopathological findings suggested axillary lymph node metastasis from endometrioid carcinoma. US-guided CNB is a valid method for accurate diagnosis of an axillary mass.