28-year-old man with acute B-lymphoblastic leukemia with standard risk was treated according to study protocol and achieved complete remission. However, molecular recurrence was detected after completion of therapy. He underwent allogeneic SCT (haploidentical graft from brother) and had complete engraftment. As complication, he developed septic arthritis, ultimately resulting in hip replacement. One year later he developed pain in the right knee with physical exercise and B-symptoms (night sweats). Clinically he showed soft tissue swelling in the area of the right knee. MRI confirmed a soft tissue mass with infiltration of tibia and PET-CT revealed generalized (inguinal, retroperitoneal, mediastinal) PET+ lymphadenopathy.