A case of phyllodes tumor with rapid growth during pregnancy and lactation period: a case report

Background The age of onset of the phyllodes tumor is generally in the late 40 s, and diagnosis and treatment during pregnancy and lactation are rare. We herein present a case of a phyllodes tumor that rapidly increased in size during the pregnancy and lactation period.Case presentation A 39-year-old woman was referred to our hospital with a mass in the right breast that increased in size during the pregnancy and lactation period. On ultrasound (5 week postpartum), a well-defined lobulated mass with internal septations and fluid retention was observed. Magnetic resonance imaging of the breast at 8 week postpartum revealed a 70-mm-sized smooth-margin mass with multilocular cystic components. Marked proliferation of stromal cells with high cell density was observed in a biopsy specimen taken at the previous hospital. We diagnosed the mass as a phyllodes tumor of borderline malignancy and excised it at 13 week postpartum. The excised tumor was 85 mm in diameter and its interior was filled with a milk-like substance. Histologically, there was only a mild increase in stromal cell density but fibrosis with associated degeneration was prominent. The final diagnosis was benign phyllodes tumor with degeneration.Conclusions We report a case of a phyllodes tumor that rapidly increased in size during pregnancy and the lactation period. The accumulation of a milk-like substance was thought to be responsible for the rapid growth of the tumor.