A high-grade breast mucoepidermoid carcinoma without MAML2 rearrangement: A case report and literature review.

INTRODUCTION: Mucoepidermoid carcinoma (MEC) of the breast is an extremely rare primary breast tumor. Between 1979 and June 2022, only 50 cases were reported. The pathological morphology and biological behavior of breast MEC remain poorly understood.

PATIENT CONCERNS: A 47-year-old female was presented with a 10-day-old left breast mass detected by physical examination.

DIAGNOSES: Ultrasonography could not distinguish whether the breast tumor was benign or malignant. After a biopsy of a breast tumor excision specimen, combined with immunohistochemical results, the patient was diagnosed with high-grade mucoepidermoid breast carcinoma.

INTERVENTIONS: The patient underwent a modified radical mastectomy for her left breast.

OUTCOMES: The patient was still free from local recurrence or metastases at 1-year follow-up.

CONCLUSION: A high-grade MEC case without MAML2 rearrangement shows good recovery without complications. The diagnosis was confirmed by histomorphology and immunohistochemical markers. It is sometimes necessary to distinguish it from adenosquamous, adenoid cystic, or mucinous carcinoma. The primary treatment is surgical resection, and the prognosis is closely related to the pathological grade.