Snapshot A 48-year-old woman presents to the physician with concern about a mass in her left breast. She notes that while doing a self breast exam a few weeks ago, she felt a small mass, but the mass has rapidly increased in size since then. On physical examination, the physician palpates a large, firm, mobile breast mass that is nontender to palpation. An incisional biopsy is performed and shows the histology seen in the image. Introduction Overview phyllodes tumor is a rare, most commonly benign breast tumor that has a leaf-like appearance on gross section (phyllon is "leaf" in Greek) and cleft-like spaces on histology Epidemiology Incidence 0.3-0.5% of female breast tumors Demographics almost exclusive in females rare cases reported in males median age is 40-49 years ETIOLOGY Pathophysiology nonepithelial neoplasm of the breast 85-90% of phyllodes tumors are benign benign phyllodes tumors may grow aggressively and can recur locally Presentation Symptoms breast mass that rapidly ↑ in size in a few weeks Physical exam firm, mobile, nontender breast mass very large phyllodes tumor may erode through skin and present as an external fungating mass shiny overlying skin over mass Imaging Mammography indications important in the diagnosis of breast lesions, but findings are unreliable at differentiating between benign phyllodes tumors, malignant phyllodes tumors, and fibroadenomas Studies Breast biopsy indications open excisional breast biopsy indicated for smaller lesions (< 5 cm) incisional breast biopsy indicated for large lesions (> 5 cm) findings long cleft-like spaces and myxoid cellular stroma Differential Fibroadenoma key distinguishing factor generally smaller than phyllodes tumors and do not exhibit rapid growth Breast abscess key distinguishing factor typically develop as a complication of mastitis localized, painful inflammation of the breast with fever Breast adenocarcinoma key distinguishing factor classic findings on mammogram include presence of a spiculated, high-density mass and grouped microcalcifications Treatment Surgical complete excision of the tumor wide local excision with a rim of normal tissue included 2 cm margin for small tumors and 5 cm margin for large tumors indicated for benign phyllodes tumors mastectomy indicated for malignant phyllodes tumors Prognosis 5-year survival for malignant tumors is 60-80%