Primary large cell neuroendocrine carcinoma of the breast diagnosed using dynamic contrast-enhanced magnetic resonance imaging and diffusion-weighted imaging: A case report.

RATIONALE: Large cell neuroendocrine carcinoma of the breast (LCNECB) is extremely rare, accounting for <0.1% of breast cancers, and has been associated with aggressive clinical behavior. Owing to its rarity, diagnostic and prognostic imaging features remain poorly defined.

PATIENT CONCERNS: A 55-year-old woman was referred for evaluation after an abnormality was detected on screening mammography. She had no personal or family history of breast cancer.

DIAGNOSES: Mammography and ultrasound revealed a left breast mass with irregular margins. Breast magnetic resonance imaging demonstrated rim enhancement, adjacent vessel sign, increased ipsilateral vascularity, and restricted diffusion. Diffusion-weighted imaging showed an apparent diffusion coefficient (ADC) of 0.745 × 10-3 mm2/s, with a peritumoral-to-tumoral ADC ratio of 2.79. Histopathology and immunohistochemistry confirmed LCNECB.

INTERVENTIONS: The patient underwent a partial mastectomy and sentinel lymph node biopsy following preoperative imaging evaluation.

OUTCOMES: The tumor measured 3.1 cm, with lymphatic invasion but no nodal metastasis. The patient did not return after surgery and was lost to follow-up; therefore, subsequent clinical outcomes could not be assessed.

LESSONS: This case highlights the diagnostic potential of breast magnetic resonance imaging in LCNECB, particularly the presence of pronounced hypervascularity and a markedly elevated peritumoral-to-tumoral ADC ratio, which may serve as valuable imaging markers for prognosis and differentiation.