Human Cancer Biology Human Melanoma Metastases Demonstrate Nonstochastic Site-Specific Antigen Heterogeneity That Correlates with T-cell Infiltration

Purpose: Metastasis heterogeneity presents a significant obstacle to the development of targeted cancer therapeutics. In this study, we sought to establish from a large series of human melanoma metastases whether there exists a determinedpattern in tumor cellular heterogeneity thatmay guide the development of future targeted immunotherapies. Experimental Design: From a cohort of 1,514 patients with metastatic melanoma, biopsies were procured over a 17-year period from 3,086 metastatic tumors involving various anatomic sites. To allow specific tumor cell profiling, we used established immunohistochemical methods to perform semiquantitative assessment for a panel of prototypic melanocyte differentiation antigens (MDA), including gp100, MART-1, and tyrosinase. To gain insight into the endogenous host immune response against these tumors, we further characterized tumor cell expression of MHC I andMHC II and, also, the concomitant CD4þ and CD8þ T-cell infiltrate. Results: Tumor cell profiling for MDA expression demonstrated an anatomic site-specific pattern of antigen expression thatwas highest in brain, intermediate in soft tissues/lymphnodes, and lowest in visceral metastases. Hierarchical clustering analysis supported that melanoma metastases have a phylogenetically determined, rather than a stochastic, pattern of antigen expression that varies by anatomic site. Furthermore, tyrosinase expression was more frequently lost in metastatic sites outside of the brain and was uniquely correlated with both endogenous CD8þ and CD4þ T-cell infiltrates. Conclusion: Site-specific antigen heterogeneity represents a novel attribute for human melanoma metastases that should be considered in future therapy development andwhen assessing the responsiveness to antigen-specific immunotherapies. Clin Cancer Res; 20(10); 2607–16. 2014 AACR.