Cathepsin K expression in a wide spectrum of perivascular epithelioid cell neoplasms (PEComas): a clinicopathological study emphasizing extrarenal PEComas

Aims Recent studies have demonstrated that cathepsin K seems to be a powerful marker in identifying renal perivascular epithelioid cell neoplasms (PEComas). However, the expression in extrarenal PEComas has not been well characterized due to their rare incidence. Our aim was to investigate the expression of cathepsin K in a wide spectrum of extrar-enal PEComas and evaluate its potential diagnostic usefulness in comparison with other commonly used markers. Methods and results Twenty-three cases of PEComa (liver, n = 9; lung, n = 1; broad ligament of uterus, n = 1; vertex subcutaneous soft tissue, n = 1; abdominal wall, n = 1; and kidney, n = 10) were selected for study. All displayed a high percentage of cells with moderately to strongly positive reactions for cathepsin K (mean 91%; range 80–100%). HMB45, Melan-A and smooth muscle actin (SMA) were expressed in 78, 87 and 87% of cases, respectively, with various percentages of positive cells (mean, 34, 40 and 38%; range 0–80, 0–90 and 0–90%). Transcription factor E3 (TFE3) was expressed strongly in only three cases; none exhibited evidence of TFE3 gene fusion or amplification. Conclusions Cathepsin K appears to be more powerful than other commonly used markers in diagnosing a wide spectrum of PEComas and distinguishing them from the majority of human cancers.