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Breast WHO 6th Edition Update: Neuroendocrine Tumors • Large cell neuroendocrine carcinoma of the breast has been eliminated as a separate entity • Tumor looks like a breast primary with moderate-to-strong (or diffuse weak but unequivocal) NE marker expression → IBC-NST with neuroendocrine differentiation. Clinical management is unchanged; treat and sign out as regular IBC-NST • Tumor looks morphologically like a NET with strong, diffuse NE marker expression → Primary breast NET (exceptionally rare). Diagnose only after metastatic NET is ruled out • Tumor looks morphologically like small cell carcinoma → Breast small cell carcinoma (rare). Diagnose only after metastasis (usually lung) is ruled out Dr. Kimberly Allison, 2026 Diagnostic Pathology Update #pathology #USCAP #PathX #BreastPath