Expression of p15 in a spectrum of spitzoid melanocytic neoplasms

Background

Accurate classification of spitzoid melanocytic lesions is difficult due to overlapping clinical and histopathologic features between Spitz nevi, atypical Spitz tumors (ASTs), and spitzoid melanomas. Expression of p16 (CDKN2A) has been used as a marker of spitzoid lesions. However, its expression may be variable. p15 is a tumor suppressor encoded by CDKN2B, loss of which has been recently shown to promote transition from nevus to melanoma. We sought to determine whether p15 is a useful immunohistochemical marker to distinguish Spitz nevi from spitzoid melanomas, and to compare p15 and p16 staining in this population.

Methods

Immunohistochemistry for p15 and p16 was performed on Spitz nevi (n=19), ASTs (n=41), and spitzoid melanomas (n=17). Immunoexpression was categorized by a four‐tiered system: 0 (negative), 1+ (weak), 2+ (moderate), 3+ (strong).

Results

3+/strong p15 staining was observed in 68.4% of Spitz nevi, 34.2% of ASTs, and 17.7% of spitzoid melanomas. By contrast, we observed 3+ p16 staining in roughly equivalent percentages of Spitz nevi (57.9%), ASTs (56.1%), and spitzoid melanomas (58.8%).

Conclusion

These data illustrate that p15 may be more useful than p16 as a biomarker to help distinguish benign from malignant spitzoid lesions.

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