Definition

A rare tumor that usually forms in the connective tissue of the breast. Cystosarcoma phyllodes of the breasts tend to grow quickly and get large, but they rarely spread to other parts of the body. Most are benign (not cancer), but some may be malignant (cancer) or borderline (in between benign and malignant). Cystosarcoma phyllodes of the breasts are usually removed by surgery, but they can come back. They are most common in women between 40 and 50 years of age. Also called CSP and phyllodes tumor.