Extramedullary Acute Myeloid Leukemia of the Renal Pelvis: Insights into a Visceral Niche.

Acute myeloid leukemia (AML) is a stem cell malignancy that originates in the bone marrow and involves the peripheral blood. Extramedullary AML is rarer, but it is most commonly associated with the former French-American-British (FAB) subtypes M4 or M5 of AML. AML cells may also home to the central nervous system and other solid organs such as cortical bone and skin. Such target sites of metastasis depend on microenvironmental niche interactions, which have not been fully elucidated to date. Visceral organs usually do not represent a favorable niche for AML stem cell occupancy. Herein, we describe the case of an 80-year-old man with extramedullary AML involvement of the renal pelvis. Hypercalcemia and obstructive uropathy were presenting features. The visceral niche is a rare site of involvement of myeloid malignancy, and hypercalcemia may reflect a mechanism of extramedullary involvement. We propose a treatment paradigm for this uncommon subset of AML based on advanced age and complex karyotype.