In marked contrast to their reduction in the primary tumor and axillary lymph node compartments, chitin monotherapy did not affect PMN- and M-MDSC, neutrophil and macrophage numbers/percentages in the spleen of 4T1 tumor-bearing mice (Fig. 8A, Additional file 15: Fig. S13A), corroborating the comparable splenomegaly in the untreated, anti-PD-1- and chitin-treated 4T1-based model (Fig. 2D). This evidence concerns the gene PDCD1 and neoplasm.