Acute promyelocytic leukemia presenting as isolated femoral granulocytic sarcoma

Background. Granulocytic sarcoma (GS), or myeloid sarcoma or chloroma, is a tumoral mass containing myeloblasts and immature granulocytes in an anatomic site other than the bone marrow. GS is very rare in children with acute promyelocytic leukemia (APL). This case report presents a rare case of GS manifesting as a solitary bone mass. Case. A 15-year-old female presented with left knee pain. Complete blood count and biochemistry were normal. No blasts or early granulocytic elements were observed in the peripheral blood smear. Magnetic resonance imaging (MRI) revealed a 4x4-cm solid lesion extending to the physis line in the distal metaphyseal section of the left femur. A Tru-cut biopsy of the mass confirmed GS with immature promyelocytic cell infiltration containing Auer rods and immature myeloid cells. The t(15;17) mutation was highly positive in the tissue suspension. Bone marrow aspiration performed afterward showed no abnormalities, and acute myeloid leukemia and acute lymphoblastic leukemia mutation panels were negative. The patient was diagnosed as having APL presenting as GS of isolated femoral origin. Treatment with standard-risk chemotherapy, including all-trans retinoic acid (ATRA) according to the BFM 2013 protocol, was initiated. After 2 months, a repeat biopsy showed no pathologic promyelocytic infiltration and a negative t(15;17) mutation. However, the patient died of severe neutropenia, sepsis, and typhoid fever. Conclusion. This case contributes to the literature as a rare presentation of APL as isolated femoral GS. It is the first reported case of an isolated femoral mass in this context to the best of our knowledge.