Breast Cancer with Cartilaginous and/or Osseous Metaplasia Diagnosed by Lymph Nodal Metastasis: A Case Report

Breast cancer with cartilaginous and/or osseous metaplasia is a type of metaplastic carcinomas and is a rare disease. We report the case of a 49 year-old female who underwent right mastectomy for a large breast tumor. Histological examinations revealed a mixed tumor with both stromal and epithelial elements; the stroma showed poor differentiated spindle-shape and multiform cells with a massive osseous matrix, and atypical epithelial cells, which mainly existed on the surface of the cysts, showed nucleic atypia. The tumor was diagnosed as a malignant phyllodes tumor with osteosarcomatous differentiation; it was not identified as a metaplastic carcinoma because of the lack of proof of a cancerous component. Two years after a mastectomy, swelling of the axillary lymph nodes was found and a biopsy was performed. Histological findings for the lymph node indicated a metastasis of the invasive ductal carcinoma. The primary tumor was re-examined and was considered to be the origin of the lymph nodal metastasis. Lymph nodal metastasis of cancer proved that the primary tumor had cancerous potential, and the pathological diagnosis was altered to a breast cancer with cartilaginous and/or osseous metaplasia.