S-100 protein in clear cell sarcomas of the tendon sheath

Fourteen histologically proved specimens of clear cell sarcomas (CCS) of tendon sheaths were studied for the presence of S-100 protein. Eleven cases were strongly positive, and 2 cases were weakly positive. There was only one case which was absolutely negative for this protein. This technique was useful to diagnose tumours which were not only easily diagnosed as CCS or soft tissue melanomas, but also in the atypical and spindle cell variants of CCS which have to be weeded out of the large family of other morphologically allied soft tissue tumours.