Abstract 4629: Macrophage number correlates with tumor stage in cutaneous melanoma
Authors: Satu Salmi, Hanna Siiskonen, Reijo Sironen, Kristiina Tyynelä-Korhonen, Päivi Auvinen, Sanna M. Pasonen-Seppänen
Journal: Cancer Research (2017)

Abstract Tumor associated macrophages and regulatory T cells (Tregs) have an important role in tumor progression as a part of the immunosuppressive tumor microenvironment. By means of immunosuppression, melanoma, as well as many other cancers, is able to resist anti-cancer immune reactions. To understand the mechanisms how tumor cells escape from the anti-tumor immune response is the key for efficient treatment strategies. In several cancers, programmed cell death ligand-1 (PD-L1) -mediated pathways have been shown to suppress anti-tumor immune responses. Our aim was to investigate the number of tumor associated macrophages (TAMs) and Tregs in benign, premalign and malign melanocytic lesions to find out if the density of these cells is associated with the tumor stage or survival in melanoma. Moreover, the expression of PD-L1 was studied. Altogether 187 tissue samples, including 29 benign and 27 dysplastic nevi, 16 in situ melanomas, 38 superficial (Breslow &amp;lt; 1 mm) and 43 deep (Breslow &amp;gt; 4 mm) melanomas and 34 lymph node metastases, were stained immunohistochemically for CD68 and CD163 representing all TAMs and M2-like macrophages, respectively and for FoxP3, a marker for Tregs. In addition, a part of the FFPE -samples was dual stained for CD68 and PD-L1. Macrophages and Tregs were counted using a hot spot -method. In the statistical analyses, the cell numbers were graded as either low or high according to the median. Non-parametric Kruskal-Wallis test was used to compare the macrophage numbers in different groups and Pearson chi-square test to study the correlations between the numbers of CD163 and CD68 -positive cells and clinicopathological parameters. CD68+ and CD163+ macrophage numbers were significantly higher in malign melanocytic lesions and lymph node metastasis compared to in situ melanomas and benign nevi. In deep melanomas and lymph node metastases macrophages located mainly inside the tumor nests whereas in thin melanomas they were mostly scattered around the tumor. High CD68+ macrophage number correlated with the presence of ulceration (p=0.011) and with both local recurrence (p=0.008) and recurrence with distal metastases (p=0.002). PD-L1 immunoreactivity was relatively scanty in melanoma samples being restricted to certain areas only; both membraneous and cytoplasmic staining was observed. Overall, the staining was higher in deep melanomas and lymph node metastases compared to superficial melanomas. Dual stainings indicated that in addition to tumor cells, a part of the tumor infiltrating CD68+ macrophages were PD-L1 -positive. The density of FoxP3+ cells did not correlate with the tumor stage. However, the number of these cells was significantly lower in benign nevi compared to other groups. Our observations highlight that TAMs are involved in melanoma progression and have an important role in the formation of an immunosuppressive tumor microenvironment. Note: This abstract was not presented at the meeting. Citation Format: Satu Salmi, Hanna Siiskonen, Reijo Sironen, Kristiina Tyynelä-Korhonen, Päivi Auvinen, Sanna M. Pasonen-Seppänen. Macrophage number correlates with tumor stage in cutaneous melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4629. doi:10.1158/1538-7445.AM2017-4629