Locally Aggressive Mixed Epithelial and Stromal Tumour of Kidney Leading to Nephron Loss

Mixed epithelial and stromal tumour (MEST) is a rare benign renal tumour. It is mainly found in perimenopausal women. We present a case of a 42-year female with no known comorbid who was presented in the outpatient clinic for the right flank pain. Contrast-enhanced CT scan revealed a complex renal cyst with internal septations. Considering a large symptomatic cyst and the presence of internal septations, she was planned for cyst excision. Peroperatively, significant disease progression and loss of renal parenchyma were noted contrary to preoperative scan. Histopathology of the specimen revealed MEST. We demonstrate that MEST of the kidney may have an aggressive local behaviour leading to nephron loss.