Pediatric case of anaplastic lymphoma kinase-positive anaplastic large cell lymphoma forming a solitary skin tumor on the forearm

A 5-year-old girl noticed a rapidly growing reddish nodule on her right forearm. Although oral antibiotics had been administrated for 2 weeks, the tumor enlarged. Skin biopsy revealed excessive infiltration of atypical neoplastic cells expressing CD4, CD30 and anaplastic lymphoma kinase (ALK). These histological and immunohistochemical findings were consistent with anaplastic large cell lymphoma (ALCL). Computed tomography showed multiple lymphadenopathy, but lymph node biopsy and bone marrow examination did not show any evidence of systemic dissemination. However, due to the positive results for ALK and multiple lymphadenopathy, we diagnosed ALK-positive ALCL forming a solitary skin tumor on the forearm. The patient received chemotherapy and presented marked improvement. This paper discusses the difficulty of diagnosing pediatric ALK-positive ALCL limited to the skin and reviews the medical published work.