Method: 89 cases from 80 patients with MPC, UCa with squamous (SQ) or glandular (GL) differentiation, small cell carcinoma (SmCa), and nested variant (NeCa) variant of UCa were identified. Histologic and clinical data including stage and outcome were collected. Results: All groups show male predominance and similar age range. MPC showed the highest rate of nodal metastases (Table 1) . Patients with MPC tumor volume of >50 % showed the highest rate of nodal metastases of all other subgroups. The majority of patients with MPC died, a large percentage from unknown causes. Compared to MPC, SQ showed similar presentation at higher stages and similar survival, but a lower propensity for nodal metastases. In our cohort, GL presented at lower stages, showed slightly better survival, and a lower rate of nodal metastases, when compared to MPC. Our cohort included fewer cases of SmCa and NeCa. However, both patients with NeCa died of disease. Conclusion: MPC, particularly when it represents >50 % of tumor volume, shows higher rate of nodal metastases than remaining subgroups, and is associated with a larger percentage of patient deaths. Objective: Müllerian-like stroma with ER/PR expression is typical of renal mixed epithelial and stromal tumor and has been described in kidneys with obstructive pathology. WT1 overexpression is not reported in this setting. Method: Immunohistochemical study for ER, PR and WT1 in autosomal dominant polycystic kidney disease (ADPKD) (n=5), acquired cystic kidney disease (ACKD) (n=5), xanthogranulomatous pyelonephritis (XP) (n=5), and renal lithiasis (RL) (n=5). Controls: fetal (<24 w, n=4; >24 w, n= 4) and adult autopsy kidneys (n=5). Results: Stromal ER was found in 100 % of ADPKD, ACKD, XP and RL; PR expression in 100 % of ADPKD, ACKD and RL and 80 % of XP, and nuclear WT1 in 20 % of XP and RL. ER were negative in 100 % of controls. We found PR expression in 100 % of fetal controls of second trimester. WT1 was negative in the stroma of adult controls (100 %). 80 % of fetal controls showed WT1 expression in the peripheral cortex. Conclusion: ER and PR expression is frequent in kidneys with chronic obstructive and inflammatory pathology. WT1 is expressed occasionally. More studies are needed to determine whether these findings are a consequence of renal obstruction or they are involved in its pathogenesis, as well as their potential therapeutic implications.