RARA and hydronephrosis: On the other hand, Marchesi et al. reported the spontaneous development of hydronephrosis due to ureteric obstructions caused by polypoid adenomas locating from the transitional epithelium of the renal pelvis to the ureter with severe cell infiltrations in promyelocytic leukemia (PML)/retinoic acid receptor, alpha (RARα) knock-in mice, a model for acute myeloid leukemia [7].