RESUMEN
BACKGROUND: We present cytogenetics and fibroblast growth factor immunohistochemistry in one case of cystosarcoma phyllodes with localized disease and one with metastatic spread. The p53 gene was sequenced in the malignant case. METHODS AND RESULTS: Karyotype analysis used trypsin-Giemsa banding. Immunohistochemistry of FGF1, FGF2, FGFR1 and p53 used avidin-biotin detection of the primary antibody. One case had a mosaic female karyotype and three clones: one normal, one with trisomy 7, and one with both trisomy 5 and a rearranged chromosome 1. In the second case, a resected pulmonary metastasis had the karyotype 43-47,XX,+mar1,+mar2[6]/43-46,XX, +del(7)(p10)[3],+mar2[1][cp3]/46,XX[10]. These tumors expressed FGF1, FGF2, and FGFR1. The malignant case showed immunostaining for p53 protein, but a wild-type gene sequence. CONCLUSION: The karyotype of cystosarcoma phyllodes is complex, with wide case-to-case variation. These tumors express members of the FGF family. Metastatic behavior can occur in the presence of a wild-type p53 gene.