Tumor-to-Tumor Metastasis: Prostate Carcinoma Metastatic to Soft Tissue Sarcoma, a Previously Unreported Event

Tumor-to-tumor metastasis is an unusual phenomenon wherein one distinct malignancy is present within the substance of another independent tumor. This event is rare, difficult to detect with imaging, and, due to conflicting terminology in the literature, can be challenging to classify. This article reports the first documented case of tumor-to-tumor metastasis involving prostatic adenocarcinoma and myxoid liposarcoma, reviews the available literature for carcinoma metastatic to sarcoma, and discusses the current situation within the context of the established criteria for the classification of combination tumors.