The immune microenvironment in typical carcinoid lung tumor, a brief report of four cases.

2020 
: Pulmonary typical carcinoid (TC) is a low-grade, rare lung cancer of neuroendocrine origin. Currently, there is very little information available about the immune cell composition in TC tumors. Here, we analyzed by flow cytometry resected tumors from four never-smoker female patients with TC. Twelve distinct immune cell types were identified in TC tumors. The most abundant immune cells were CD8+ T cells, CD4+ T cells, B cells, and macrophages, which represented 19.8%, 17.7%, 11.5%, and 11% of all tumor-infiltrating CD45+ leukocytes, respectively. Natural killer (NK) cells (8.9%) and neutrophils (3.9%) were also common. Three types of dendritic cells (DCs) were identified (plasmacytoid DCs, CD1c+ DCs, and CD141+ DCs) which together constituted 1.4% of all immune cells in TC tumors. Small populations of basophils (1.3%), mast cells (0.8%), and eosinophils (0.6%) were also present. Notably, the percentage of leukocytes (of all living cells) was much lower in TC tumors compared to high-grade non-small cell lung cancer (NSCLC) tumors, and also compared to non-cancerous lung tissue. We conclude that TC tumors are relatively non-inflammatory, although the immune landscape was found to be very complex.
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