Pleomorphic fibroma and dermal atypical lipomatous tumor: are they related?

Pleomorphic Fibroma Presenting as a Nodular Lesion in the Left Shoulder: A Case Report

Pleomorphic fibroma is an uncommon benign cutaneous tumor that often presents as a single asymptomatic skin-colored lesion with indefinite clinical diagnostic features. Here, we report a case of a 47-year-old female diagnosed with pleomorphic fibroma of the skin in the left shoulder and discuss the importance of immunohistochemistry and special features in histopathology to distinguish some of the differentials.

Histopathologic and Genetic Findings in Atypical Spindle Cell/Pleomorphic Lipomatous Tumors and Atypical Pleomorphic Fibromas

BACKGROUND

Spindle cell lipomas, pleomorphic lipomas (SCL/PLs) and pleomorphic fibromas (PF) are tumors with loss of retinoblastoma (RB). The latest World Health Organization classification includes a category of atypical spindle cell/pleomorphic lipomatous tumors (ASPLT) that encompasses tumors in this spectrum that show atypical histopathologic features. We have observed PFs that show similar atypical features.

METHODS

Cases of SCL/PL and PF with atypical features were collected from tissue archives between 2010-2019. Genetic alterations were investigated using array comparative genomic hybridization (aCGH).

RESULT

Of 15 cases found, most tumors were dermal-based with fibrocytic or fibroadipocytic appearance and occasional lipoblasts. All cases had a high proliferation index with atypical mitotic figures in 71% of cases. Chromosome 13q loss was present in all cases with CGH data. Additional recurrent chromosomal losses included 17p, 16q, 17q, 20p, 4, and 10. No recurrence was found in limited follow up.

CONCLUSIONS

ASPLTs are characterized by loss of RB, prominent nuclear pleomorphism, mitotic activity including atypical mitotic figures, and genomic instability with multiple chromosomal aberrations. A similar group of tumors with these histopathologic features lacks lipomatous differentiation, and we propose the diagnosis of atypical PF as a fibromatous variant of ASPLT. Limited clinical follow up appears benign.

Pleomorphic Fibroma: A Clinicopathologic Case Series With the Review of the Literature

BACKGROUND

Pleomorphic fibromas are rare flesh-colored benign neoplasms first described in 1989. Their histopathology is notable for nuclear pleomorphism of spindle cells and multinucleate giant cells but lacking mitoses. The cellular origin of these tumors is unknown. This case series describes an additional 18 lesions with discussion of histopathology and immunohistochemistry.

METHODS

This case series of 18 pleomorphic fibromas uses immunohistochemical staining for CD34, CD68, factor XIIIa, and S-100 and general histopathologic examination under light microscopy to describe the lesions.

RESULTS

Immunohistochemical stains for CD34 showed nearly universal positivity of the pleomorphic spindle cells, although some more focally. The pleomorphic cells were negative for CD68, variably positive for factor XIIIa, and universally negative for S-100. All the lesions showed characteristic nuclear pleomorphism with absent mitoses. Collagen thickening was variable, mucin was absent, and perivascular inflammation was present in all lesions.

CONCLUSIONS

Pleomorphic fibromas are fibrous lesions with benign clinical course and histopathologic findings including nuclear pleomorphism. Immunohistochemical staining characteristics of the lesion, along with unique spindle cells and multinucleate giant cells help to differentiate this from other tumors.

Pleomorphic fibroma of the skin with MDM2 immunoreactivity: A potential diagnostic pitfall

Pleomorphic fibroma is a rare benign cutaneous neoplasm characterized by spindle-shaped cells and multinucleated giant cells scattered throughout collagenous stroma. These morphologic features can lead to diagnostic confusion, including atypical lipomatous tumor as one consideration. In contrast to atypical lipomatous tumor, previous studies have found pleomorphic fibroma to be negative for MDM2 immunohistochemical staining and MDM2 gene amplification. Here, we present a case of pleomorphic fibroma of skin with nuclear MDM2 immunoreactivity in the absence of MDM2 gene amplification, underscoring the superiority of fluorescence in situ hybridization as a diagnostic test in this differential diagnosis. The RB1 locus is also explored for differential diagnosis with pleomorphic/spindle cell lipoma and related entities.

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

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.