Loss of retinoblastoma in pleomorphic fibroma: An immunohistochemical and genomic analysis

Abstract

Background: Pleomorphic fibroma is a curious neoplasm that exhibits striking cytologic atypia, yet behaves in benign fashion. The cytologic features include single cells with pleomorphic nuclei and scattered giant cells resembling the neoplastic cells of pleomorphic lipoma, a tumor with known retinoblastoma (Rb) loss.

Methods: We assessed the demographic and histopathologic features of a cohort of 26 pleomorphic fibromas, including assessment with immunostaining for Rb, p16 and Ki-67. Array comparative genomic hybridization (aCGH) was used to assess a limited number of tumors for genomic aberrations.

Results: Of the 26 pleomorphic fibromas analyzed, 19 occurred in women and 7 in men, with a mean age of 47 years. The anatomic locations were variable. Immunostaining showed loss of Rb protein expression in all cases and diffuse p16 expression in 85%. Ki-67 labeling rate was below 10% in 85%. Chromosome 13q loss was found in 7 of 7 pleomorphic fibromas assessed with aCGH. Recurrent loss of 17p, 16q and 10q were also found.

Conclusion: We report recurrent loss of RB1 on chromosome 13q in pleomorphic fibromas, confirmed by both protein expression loss and loss of 13q by aCGH. This result indicates pleomorphic fibroma shares the same genetic abnormalities as spindle cell and pleomorphic lipomas.

Keywords: RB1; pleomorphic fibroma; pleomorphic lipoma; retinoblastoma; spindle cell lipoma.