PAX5-expressing ALK-negative anaplastic large cell lymphoma with extensive extranodal and nodal involvement.

A 55-year-old man with a history of well controlled HIV infection was admitted with acute renal impairment, peripheral oedema, constitutional symptoms, deranged liver function and hypercalcaemia. Core biopsies of a retroperitoneal mass demonstrated anaplastic lymphoma kinase (ALK) negative anaplastic large cell lymphoma (ALCL) with unusual Paired box 5 (PAX5) positivity. The same malignant cells were identifiable on urine cytology. Staging investigations revealed extensive nodal and extranodal disease including ALK negative ALCL involving the kidney and prostate, which has not previously been reported in the published literature.