Expression of MLH1 and MSH2 in urothelial carcinoma of the renal pelvis.

In this study, we investigated microsatellite instability in urothelial carcinoma of the renal pelvis by lack of immunohistochemical staining for MLH1 and MSH2. The study included 44 cases of urothelial carcinoma of the renal pelvis obtained from radical nephroureterectomy specimens at our institution. We evaluated the loss of nuclear immunohistochemical staining of MLH1 and MSH2. Eight of 44 (18 %) patients had negative MLH1 expression and 25/44 (57 %) patients had negative MSH2 expression. Six of 8 (75 %) patients with negative MLH1 expression were male and 2/8 (25 %) patients were female. Nineteen of 25 (75 %) patients with negative MSH2 expression were male, and 6/25 (24 %) patients were female. Seven of 8 (88 %) cases with negative MLH1 expression were high-grade urothelial carcinoma, and 21/25 (84 %) cases with negative MSH2 expression were high-grade urothelial carcinoma. Twenty-one of 44 (48 %) cases had an inverted growth pattern, of which 3/21 (14 %) cases had negative MLH1 expression and 14/21 (67 %) cases had negative MSH2 expression. Our study showed that microsatellite instability based on negative expression of MLH1 and MSH2 was more common in male patients with high-grade urothelial carcinoma. There is a strong correlation between inverted growth pattern and negative MSH2 expression. Microsatellite instability testing should be performed in patients with upper urinary tract carcinoma and may have prognostic value.