Search

It is often very difficult to confidently distinguish benign and malignant Spitz lesions, and a diagnosis of Spitz tumor of unknown malignant potential (STUMP) is rendered. To address this problem, we performed molecular genetic analysis in a large group of Spitz tumors (93 Spitz nevi and 77 STUMPs) and identified a subgroup of 24 lesions harboring a HRAS mutation. This subgroup lay predominantly in the dermis, had a relatively low cellularity, showed desmoplasia (with single cells interspersed between the collagen bundles), and had an infiltrating base. In 7 of these 24 cases (29%) melanoma had been the initial diagnosis, or an important differential diagnostic consideration, mainly based on the presence of multiple or deeply located mitotic figures, especially in adult patients. In our series none of the patients with the HRAS-mutated lesions developed recurrences or metastases (mean and median follow-up: 10.5 y). This was in accordance with the literature: review showed that no HRAS mutations had so far been reported in Spitzoid melanomas. We therefore conclude that HRAS mutation analysis may be a useful diagnostic tool to help differentiate between Spitz nevus and Spitzoid melanoma, thereby reducing the frequency of overdiagnosis of melanoma, and to help predict the biological behavior of a STUMP. Moreover, this might be a first step toward a more reproducible classification of Spitz tumors combining histological and genetic data.

A definite diagnosis cannot be established based on histologic features alone in a large number of Spitz nevi and spitzoid melanomas. In a vast majority of common benign and malignant melanocytic lesions, B-RAF and N-RAS mutations were described, but these were not detected in Spitz nevi. In contrast, H-RAS mutations were frequently encountered in Spitz nevi, but only rarely in melanomas. To date, B-RAF mutation analysis has not been reported in atypical Spitz nevi, and there are only a few reports of it in spitzoid melanomas. We analyzed 96 formalin-fixed, paraffin-embedded spitzoid melanocytic lesions for hotspot mutations in B-RAF, N-RAS, and H-RAS genes to test the assumption whether mutation analysis would assist a more accurate diagnosis of spitzoid melanocytic lesions, which are notoriously difficult to classify. B-RAF or N-RAS mutations were observed in 31 of 36 (86%) spitzoid melanomas, and in 6 of 7 (86%) spitzoid melanoma metastases. In contrast, none of the 14 Spitz nevi and none of the 16 atypical Spitz nevi had mutations in any of the three genes. A B-RAF or N-RAS mutation was found in 8 of 23 (35%) spitzoid lesions suspected for melanoma. H-RAS mutations were detected in 4 of 14 (29%) Spitz nevi, in 3 of 22 (14%) atypical Spitz nevi, in 1 of 15 (7%) spitzoid tumors suspected for melanoma, but in none of the spitzoid melanomas. These results strongly indicate that Spitz nevi and spitzoid melanomas are genetically unrelated entities. Furthermore, we can conclude that mutation analysis may be useful as an additional diagnostic tool to distinguish between benign and malignant spitzoid lesions.