RESUMEN
A premenarcheal 10-year-old girl visited our clinic due to a rapidly growing and painless mass of the right breast of three months duration. The breast mass was removed using a wide local excision. The pathological findings revealed the tumor was made up of a phyllodes tumor. A phyllodes tumor, also known as cystosarcoma phyllodes, is a rare fibroepithelial tumor of the breast, which accounts for 0.3 to 1.0 % of all breast neoplasms. They have a greater degree of stromal cellularity than fibroadenomas, with a characteristic leaf-like projection. These tumors can occur between the ages of 9 to 88 years, but are most common in the third and fourth decades of life; therefore, are uncommon in children. A phyllodes tumor in an adolescent patient was first studied by Amerson, in 1970, at which time he reviewed 355 cases from the American literature, and found a five percent incidence in subjects below 20 years old. Because only a few cases have been reported in the literature; here we report a case of a phyllodes tumor in a 10-year-old girl.