Rap1-GAP protein was detected in 15/19 subsequently recurring primary melanomas (79%) but only in 32/67 tumors (47%) of patients who remained free of disease (P < 0.05) for at least 6 years.     ///    In the latter group the frequency of Rap1-GAP expression increased (P < 0.05) with the thickness of primary tumors and was highest in metastatic lesions.     ///    In the present immunohistochemical study we analyzed the clinicopathological and prognostic relevance of Rap1-GAP expression in 60 benign and 103 malignant melanocytic tumors.     ///    "Although being no indicator for malignant transformation of melanocytic lesions, Rap1-GAP overexpression may represent a useful marker for identifying thin high-risk melanomas. "    ///    Clinicopathological and prognostic relevance of Rap1-GAP expression in melanocytic tumors..     ///    "Cytoplasmic expression of Rap1-GAP has also been observed in the cells of skin appendages and in keratinocytes, particularly in suprabasal layers of the epidermis. "    ///    "Therefore, Rap1-GAP is likely to be associated with cellular growth and/or differentiation. "    ///    " Rap1-GAP protein has been identified as an inactivator of Rap1 activity, a putative endogenous antagonist of Ras proteins. "