Primary cutaneous anaplastic large‐cell lymphoma with DUSP22‐IRF4 rearrangement following insect bites

Primary cutaneous anaplastic large‐cell lymphoma (pC‐ALCL) is distinguished from systemic anaplastic large‐cell lymphoma (S‐ALCL) with cutaneous involvement. Although pC‐ALCL is a unique entity with different genetics, clinical characteristics, and prognosis, its causes are unknown. Herein, we report the case of a Chinese woman with a 4‐month history of a gradually enlarged ulcerative mass in her right forearm following an unidentified insect bite. Biopsy revealed an extensive infiltrate with patches of large anaplastic lymphoid cells. These cells were immunohistochemically positive for CD45, CD30, and TIA‐1 and negative for CD2, CD3, CD4, CD5, CD20, CD7, CD8, and ALK‐1. DUSP22‐IRF4 rearrangement was detected; on the other hand, TP63 rearrangement was not observed by fluorescence in situ hybridization (FISH). No Epstein‐Barr virus‐encoded small RNAs (EBERs) were detected by ISH. Rearrangement of monoclonal TCR gene was found using BIOMED‐2 polymerase chain reaction. No abnormality was found on the subsequent positron emission tomography‐computed tomography (PET‐CT) scan. After five cycles of cyclophosphamide + doxorubicin + vincristine + prednisolone (CHOP) chemotherapy, the patient achieved complete remission. This is the first report of a unique pC‐ALCL with DUSP22‐IRF4 rearrangement following an insect bite other than S‐ALCL involving the skin.