Abstract
Background: Melanocytic tumors arising in blue nevus (MTBN) are known to be diagnostically challenging. Immunohistochemistry and molecular approaches have been used as ancillary diagnostic tests. Herein we investigate the use of PRAME immunohistochemistry (IHC) for the assessment of MTBN.
Methods: 22 benign blue nevi and variants, 19 atypical blue nevi tumors, and 12 melanomas arising in blue nevus were retrieved and PRAME IHC was scored on a scale of 1-4 (in % quartiles). Intensity of staining was categorized as weak or strong. Cases with no staining received a score of 0. Positive lymph nodes from one melanoma was also analyzed.
Results: Blue nevi (and variants), atypical blue nevus tumors, and melanomas arising in blue nevus had mean PRAME IHC scores of 0.1, 0.3, and 2.5 respectively. The percentage of cases with a score 3 or higher for each category of spitzoid neoplasms are as follows: nevus (0%), atypical (5%), and melanoma (58%). Among the melanomas, one case had positive sentinel lymph node which demonstrated strong PRAME staining in the metastatic deposit. PRAME IHC scores for nevi versus melanomas and atypical versus melanoma were statistically signification at p=1.3x10-3 and p=2.0x10-3, respectively.
Conclusions: Previous reports revealed PRAME IHC as useful to distinguish benign from malignant melanocytic lesions. The results presented here are concordant with the prior studies but expand the application of this marker to the MTBNs. The present findings suggest the potential diagnostic utility of PRAME IHC in the assessment of MTBN lesions, particularly distinguishing malignancy from benign and atypical counterparts.