Unusual presentation of common acute lymphoblastic leukemia antigen-positive extramedullary disease in childhood.  Two patients with isolated masseter muscle involvement. 
Two children with unusual extramedullary common acute lymphoblastic leukemia antigen (CALLA)-positive (CD10) disease are reported.  Isolated masseter infiltration with CD10/CD19-positive lymphoblasts was present in both patients with no other evidence of disease.  One child had relapse of common acute lymphoblastic leukemia, and the other had primary disease.  Disease may have spread from lymph nodes overlying the masseter muscle.  Immunophenotyping and immunogenotyping provided a rapid and accurate diagnosis for both children.