Atypical fibrous histiocytoma of the skin with CD30 and p80/ ALK1 positivity and ALK gene rearrangement

We report the case of a two patients who presented with a solitary, asymptomatic, angiomatoid nodule on the right thigh. Histopathological finding showed a poorly circumscribed lesion, located in the dermis. The morphological aspect strongly suggested the diagnosis of atypical fibrous histiocytoma ( AFH ), but surprisingly, the neoplastic cells were diffusely CD30 +, with a membrane staining devoid of paranuclear dot. The lesions were tested for p80/ ALK1 expression. Surprisingly, we found a diffuse cytoplasmic positivity. Interestingly, using break‐apart fluorescent in situ hybridization ( FISH ), we evidenced an ALK rearrangement in nearly 50% of the neoplastic cells. The expression of CD30 and ALK1 with ALK gene rearrangement raised the possibility of three diagnoses: a primary cutaneous anaplastic large cell lymphoma ( ALCL ), a cutaneous inflammatory myofibroblastic tumor ( IMT ), an AFH of the skin associated with ALK gene rearrangement and CD30 positivity. The three hypotheses were discussed and finally, although p80/ ALK1 expression and cytogenetic abnormalities in fibrous histiocytoma ( FH ) are not yet reported to the best of our knowledge, we favored the diagnosis of AFH .