Recent studies have demonstrated that
cathepsin K seems to be a powerful marker in identifying the
microphthalmia associated transcription factor (MITF) family
tumors such as renal
perivascular epithelioid cell neoplasms (
PEComas),
alveolar soft part sarcoma, and translocation-associated
renal cell carcinomas. However, the expression of
cathepsin K in melanocytic lesions has not been well characterized. Our aim was to investigate the expression of
cathepsin K in a wide histological spectrum of melanocytic lesions and to evaluate its potential diagnostic and molecular target
therapy usefulness in comparison with other commonly used markers. 143 consecutive melanocytic lesions were selected for study including 56 primary
malignant melanomas, 62 metastatic
melanomas, and 25 benign
nevi (16 intradermal
melanocytic nevi and 9 compound
melanocytic nevi). 107 of the 118 (91%) primary and metastatic
melanomas displayed a high percentage of cells with moderately to strongly positive reactions for
cathepsin K (mean 82%; range 0-95%). MITF, HMB45,
Melan-A, and S100 were expressed in 85, 76, 78 and 96% of cases, respectively, with various percentages of positive cells (mean, 63, 49, 55 and 86%; range 0-90, 0-80, 0-90 and 0-95%). Among the benign
nevi,
cathepsin K, MITF, HMB45,
Melan-A, and S100 were expressed in 88, 80, 36, 68 and 100% of cases, respectively.
Cathepsin K appears to be consistently and strongly expressed in melanocytic lesions and valuable in distinguishing
malignant melanomas from the majority of human
cancers.