Phyllodes tumor in a patient with a preexistent fibrocystic disease.

A phyllodes tumor appeared at the site of a resected fibrocystic disease focus. Administration of danazol resulted in temporary regression, but the tumor resumed growth. Relative hyperestrogenism also continued to increase in spite of continued long-term administration of danazol. After 12 months a simple mastectomy was performed. Most of the resected mass consisted of the phyllodes tumor, but it also contained fibrocystic disease.