# Occult breast cancer discovered due to a large mass in the axilla: a case report

## TL;DR

A 77-year-old woman was diagnosed with occult breast cancer after a mass in her axilla revealed metastasis, despite no visible tumor in the breast.

## Contribution

This case report highlights the diagnostic challenge of occult breast cancer presenting as axillary lymph node metastasis without a palpable breast lesion.

## Key findings

- The patient had axillary lymph node metastasis of breast cancer diagnosed via histopathology.
- Breast MRI showed no malignancy in the right breast, leading to a total mastectomy.
- The patient was diagnosed with ductal carcinoma in situ and is undergoing endocrine therapy.

## 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.