MSH: A type of connective tissue neoplasm typically arising from intralobular stroma of the breast. It is characterized by the rapid enlargement of an asymmetric firm mobile mass. Histologically, its leaf-like stromal clefts are lined by EPITHELIAL CELLS. Rare phyllodes tumor of the prostate is also known.,NCI: A type of tumor found in breast or prostate tissue. It is often large and bulky and grows quickly. It may be benign (not cancer) or malignant (cancer) and may spread to other parts of the body.,NCI: A benign, borderline, or malignant fibroepithelial neoplasm arising from the breast and rarely the prostate gland. It may recur following resection. The recurrence rates are higher for borderline and malignant phyllodes tumors. In borderline and malignant phyllodes tumors metastases to distant anatomic sites can occur. The incidence of metastases is higher in malignant phyllodes tumors.