Breast Cancer Metastasis to the Upper Arm: A Rare Case and Review of the Literature.

INTRODUCTION

Soft tissue metastasis of breast cancer is very rare. Specifically, metastasis to the upper arm has only been reported in 10 cases, including this one, to the best of our knowledge. Distant lymph node metastasis of breast cancer is also infrequent, with only one documented case of brachial lymph node metastasis.

CASE PRESENTATION: We report a case of soft tissue or lymph node metastasis in the right upper arm, diagnosed 3 years after surgery for right breast cancer. The patient, a 79-year-old woman, was receiving postoperative hormone therapy for right breast cancer. She presented with edema and numbness in the right upper arm during a routine follow-up examination 3 years post-surgery. Ultrasonography revealed a 20 mm mass in the right brachial muscle, which was diagnosed as adenocarcinoma via fine-needle aspiration, suggesting breast cancer metastasis. Further examination showed that the mass was in close proximity to the nerves and veins, but no definitive evidence of invasion was observed. Surgical resection was performed. The tumor was particularly adherent to the nerve, complicating resection. While no gross residual tumor was noted, histopathological analysis indicated positive surgical margins. After surgery for soft tissue or lymph node metastasis, the patient continued hormone therapy postoperatively. However, approximately 1 year and 3 months later, tumor recurrence at the resection site and skin metastasis were observed. Consequently, hormone therapy was modified, and oral cyclin-dependent kinase 4/6 (CDK4/6) inhibitors were initiated.

CONCLUSIONS

Metastasis of breast cancer to soft tissue and the brachial lymph nodes is extremely rare. Diagnosis may be delayed in asymptomatic cases, and when metastasis is in close proximity to surrounding structures, such as the nerves, histological diagnosis can be challenging. Metastatic soft-tissue tumors are associated with a poor prognosis; therefore, early diagnosis and appropriate multimodal treatment are crucial.