Case Report: A primary breast collision tumor composed of myeloid sarcoma and invasive ductal carcinoma.

Collision tumors, characterized by the coexistence of distinct malignant neoplasms within the same anatomical site, are rare in the breast. We present a case of a 53-year-old woman with an incidentally discovered palpable mass in the upper inner quadrant of the left breast. Preoperative hematological evaluation was unremarkable. Comprehensive imaging evaluation, including ultrasound, mammography, MRI, and PET-CT, was suggestive of malignancy. A preoperative core needle biopsy was performed but yielded limited material, with pathology suggestive of possible invasive ductal carcinoma, necessitating definitive surgical excision for diagnosis. Following breast-conserving surgery and sentinel lymph node biopsy, histopathological and immunohistochemical analysis revealed a collision tumor composed of myeloid sarcoma (MS) and invasive ductal carcinoma (IDC), the latter exhibiting a triple-negative phenotype (ER-, PR-, HER2-), with no lymph node metastasis. This case highlights the clinicopathological and imaging features of this rare entity and underscores the integral role of multimodal imaging, thorough pathological evaluation, multidisciplinary collaboration, and the limitations of biopsy in heterogeneous lesions in diagnosis and management.