Phyllodes Tumor: 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.Fibroadenoma: An adenoma containing fibrous tissue. It should be differentiated from ADENOFIBROMA which is a tumor composed of connective tissue (fibroma) containing glandular (adeno-) structures. (From Dorland, 27th ed)Neoplasms, Fibroepithelial: Neoplasms composed of fibrous and epithelial tissue. The concept does not refer to neoplasms located in fibrous tissue or epithelium.Adenofibroma: A benign neoplasm composed of glandular and fibrous tissues, with a relatively large proportion of glands. (Stedman, 25th ed)Mastectomy, Simple: Removal of only the breast tissue and nipple and a small portion of the overlying skin.Breast Neoplasms: Tumors or cancer of the human BREAST.Stromal Cells: Connective tissue cells of an organ found in the loose connective tissue. These are most often associated with the uterine mucosa and the ovary as well as the hematopoietic system and elsewhere.Biopsy, Large-Core Needle: The use of needles usually larger than 14-gauge to remove tissue samples large enough to retain cellular architecture for pathology examination.Tumor Markers, Biological: Molecular products metabolized and secreted by neoplastic tissue and characterized biochemically in cells or body fluids. They are indicators of tumor stage and grade as well as useful for monitoring responses to treatment and predicting recurrence. Many chemical groups are represented including hormones, antigens, amino and nucleic acids, enzymes, polyamines, and specific cell membrane proteins and lipids.Immunohistochemistry: Histochemical localization of immunoreactive substances using labeled antibodies as reagents.