High-grade, poorly differentiated breast carcinoma mimicking primary breast lymphoma: a case report of a diagnostic dilemma

Background: High-grade breast carcinomas can occasionally exhibit morphological and immunophenotypic features resembling hematolymphoid neoplasms, leading to diagnostic confusion. Accurate diagnosis is essential to guide appropriate therapy. Case presentation: We report a 35-year-old female presenting with a rapidly enlarging right breast mass. Core biopsy revealed sheets of atypical lymphoid-like cells. Immunohistochemistry (IHC) showed positivity for cytokeratin, progesterone receptor, CD10, CD117, and BCL2, while CD20, CD3, estrogen receptor, and HER2 were negative, with Ki-67 > 95%. Despite initial suspicion of primary breast lymphoma, the overall clinicopathologic correlation favored a diagnosis of high-grade, poorly differentiated invasive breast carcinoma. Discussion: This case highlights a rare diagnostic pitfall where breast carcinoma mimics lymphoma. Careful histopathologic evaluation, comprehensive IHC profiling, and clinicopathologic correlation are crucial to avoid misdiagnosis and ensure timely management. Conclusion: Awareness of such mimicry can prevent unnecessary hematolymphoid-directed therapy.