Relapse of acute lymphoblastic leukemia in the inferior rectus muscle of the eye

Background. Extramedullary involvement of acute lymphoblastic leukemia (ALL) in sites outside the central nervous system (CNS) or testes is rare and may signal a refractory form of leukemia. Methods. The authors describe a child with ALL who experienced a relapse involving the inferior rectus muscle of the eye. This patient had been treated with a bone marrow transplant for previous bone marrow and ovarian relapse. Results. The patient had a pre‐B ALL with a t(1;19) chromosomal translocation and previously had experienced relapse during therapy. At the time of the muscle relapse, she had pancreatomegaly consistent with leukemic infiltration but no CNS or bone marrow disease. Conclusions. Relapse of ALL in unusual sites may indicate disease that is particularly difficult to eradicate. Factors in addition to age and leukocyte count at diagnosis determine risk. Additional research is needed to define these factors and develop more effective therapy.