Napsin A was immunoreactive in 2 of 2 (100%) acquired cystic disease associated RCC, 3 of 3 (100%) metanephric adenoma, 0 of 1 (0%) mucinous tubular and spindle cell carcinoma, and 0/1 (0%) TFE/MITF RCC. This evidence concerns the gene MITF and renal cell carcinoma.