Mod Pathol 2017 03 13;30(3):357-369. Epub 2017 Jan 13.
Dermatopathology Section, Department of Pathology and Laboratory Medicine (113), VA Integrated Service Networks (VISN1), West Roxbury, MA, USA.
Recently, patients with metastatic desmoplastic melanoma (DM) have been shown to respond more favorably to anti-PD1/PD-L1 therapy than other melanoma subtypes. Given this, we evaluated PD-L1/2 expression in primary DM samples and correlated these with subtype, CD8+ lymphocyte status, histopathological prognosticators, and select genetic alterations. Eighty-six (36 mixed DM, 50 pure DM) archival annotated samples met inclusion criteria and were immunohistochemically semiquantitatively evaluated. Per established criteria, for PD-L1/L2, cases with ⩾5% tumoral expression, and for CD8, cases with a predominantly peri/intratumoral CD8+ infiltrate were scored positive. Univariate analysis (chi-square and Wilcoxon) identified potential confounders and a nested case-control study was accomplished using multiple logistic regression. For PD-L1, 49% of cases were positive and 71% of cases with thickness >4 mm were positive; PD-L1 expression differed by median depth (3.29 mm, interquartile range=3.58 mm for PD-L1 positives vs 1.75 mm, interquartile range=2.04 mm for PD-L1 negatives, P=0.0002) and was linearly associated with increasing depth of invasion (P=0.0003). PD-L1-positive cases were more likely to display CD8+ lymphocytes (60 vs 28% P=0.0047).The presence of CD8+ lymphocytes correlated significantly with depth of invasion >1 mm (P=0.022). On multivariate analysis, PD-L1 was 6.14 × more likely to be expressed in mixed DM than pure DM (P=0.0131), CD8+ staining was 6.22 × more likely in PD-L1 positive cases than in PD-L1 negative (P=0.0118), and tumor depth was associated with greater odds of PD-L1 expression (OR=1.61, P=0.0181). PD-L2 expression was observed in 48% of cases but did not correlate with any variables. Correlation of tumoral PD-L1 with increased depth and CD8+ lymphocytes implicates the tumoral immune microenvironment with advancing disease in DM. Enhanced tumoral PD-L1 expression in the mixed cytomorphological variant provides an insight into the differential pathogenesis of the subtypes and suggests that these patients are likely better candidates for anti-PD/PD-L1 therapy.