Anaplastic Lymphoma Kinase (ALK)-Positive Large B-cell Lymphoma in Children: A Case Report and Review of Literature.

Anaplastic lymphoma kinase-positive large B-cell lymphoma (ALK⁺-LBCL) is an aggressive and rare B-cell lymphoma caused by the ALK gene mutation. It is exceptionally rare in children and typically presents at advanced stages. Due to morphological mimicry of other hematologic malignancies and conditions, diagnosis remains challenging. Moreover, prognosis is poor as there is a lack of standard therapy. We report the case of a 13-year-old Indonesian male who presented with abdominal pain, initially presumed to be appendicitis. Multiple abdominal masses were subsequently identified following surgery. Histopathological examination revealed diffuse sheets of large round cells with plasmablastic morphology and numerous mitotic figures. Immunohistochemical analysis demonstrated positive ALK expression with a granular cytoplasmic pattern, weak CD45 expression, strong positivity for CD38, MUM1, and EMA, a Ki-67 proliferation index of approximately 70%, and negativity for B- and T-cell markers. Staging confirmed ALK⁺-LBCL, stage IV, according to the Murphy and St. Jude Children's Research Hospital staging system, with both nodal and extranodal involvement. The patient was treated with CHOP chemotherapy, with alectinib added from the second cycle. A partial response was achieved after four cycles and was sustained for more than one year. Notably, neuron-specific enolase levels increased in parallel with disease progression. This case highlights diagnostic challenges related to an unusual clinical presentation and pathological overlap with other hematologic diseases.