For reasons that remain mysterious, PCDLBCL most commonly involves the lower leg and PCDLBCL-leg type (PCDLBCL-LT) is recognized as a specific entity in the WHO classification of lymphoma.2 It predominantly affects older patients and is associated with poor response to conventional therapy.3 The majority of PCDLBCL-LTs exhibit an ABC DLBCL gene expression profile and are strongly enriched for genetic activation of the BCR pathway, suggesting a pathogenesis shared with nodal ABC DLBCL.4,5. The gene discussed is BCR; the disease is aneurysmal bone cyst.