Abstract
Background. Significant decreases in p16 expression have been shown to occur in melanoma compared to Spitz tumors, and loss of p16 staining has been found to correlate with melanoma tumor progression. However, comparison of p16 between atypical cellular blue nevi (CBN) and melanoma has not been reported previously. Methods. p16 immunohistochemical staining was evaluated in 14 atypical CBN, 8 conventional and atypical melanocytic nevi, and 16 melanomas, including 4 malignant CBN. p16 staining intensity was graded on a scale of 0–3 and the percentage of melanocytes stained with p16 was determined. Results. p16 staining was significantly higher in all CBN as a group when compared to melanomas (P = 0.001) and malignant CBN (P = 0.00008). Higher p16 expression was also seen in mildly (P = 0.0002) and moderately atypical (P = 0.02), but not severely atypical, CBN compared to melanomas. Conclusions. p16 immunohistochemical expression is higher in mildly and moderately atypical CBN compared to severely atypical CBN and melanomas. In conjunction with additional markers and histology, p16 staining may be useful in confirming the benign nature of these tumors, but is not useful in distinguishing severely atypical CBN from malignant cases, consistent with the overlapping histologic features between these tumors.
Highlights
Distinguishing atypical and unusual variants of melanocytic nevi from melanoma by routine histologic examination can be difficult in some cases [1,2,3]
A similar, and in some instances an even stronger difference between cellular blue nevi (CBN) and malignant CBN was found for p16 staining intensity (2.22 ± 0.18 versus 0.94 ± 0.33, P = 0.02) and percentage of positive melanocytes staining with p16 (52.4 ± 8.33 versus 6 ± 3.24, P = 0.00008) (Figures 1(a) and 1(b), Table 3)
10 of 12 melanomas displayed only very low levels of p16 staining, with 0– 12.5% of melanocytes staining for p16, one superficial spreading melanoma did not show significant loss of p16, and a nevoid melanoma had moderate levels of p16 staining
Summary
Distinguishing atypical and unusual variants of melanocytic nevi from melanoma by routine histologic examination can be difficult in some cases [1,2,3]. P16 has been shown to be decreased or absent in melanoma compared to benign melanocytic nevi [9,10,11,12,13], including congenital melanocytic nevi [14] P16 immunohistochemical staining was evaluated in 14 atypical CBN, 8 conventional and atypical melanocytic nevi, and 16 melanomas, including 4 malignant CBN. P16 immunohistochemical expression is higher in mildly and moderately atypical CBN compared to severely atypical CBN and melanomas. In conjunction with additional markers and histology, p16 staining may be useful in confirming the benign nature of these tumors, but is not useful in distinguishing severely atypical CBN from malignant cases, consistent with the overlapping histologic features between these tumors
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