Omega-3 polyunsaturated fatty acids (n-3 PUFA) have been found to be modulators of immune function. Additionally, they may affect the growth of colorectal cancer (CRC). With the advent of novel treatment approaches in oncology targeting immune checkpoint inhibition and aiming to boost the immune response against tumors the exact role of n-3 and n-6 PUFA in inflammation as well as in CRC needs to be re-evaluated in order to understand potential interactions with these new treatment paradigms. Interestingly, for the cyclooxygenase (COX) inhibitor aspirin a possible synergistic effect together with a PD1-Ligand antibody has been shown. However, could n-3 PUFA be disadvantageous in the context of immune tumor therapy due to an immune suppressive effect that has been described for these fatty acids in the past, or could they also enhance the effect of immune checkpoint inhibition? In this paper, we discuss the current data regarding the immune modulatory as well as the anti-CRC effect of n-3 PUFA. Arguing towards an immune-activating effect of n-3 PUFA, we demonstrate the results of a pilot study. Here, we show that incubation of human peripheral blood mononuclear cells (PBMCs) with the n-3 PUFA docosahexaenoic acid (DHA) significantly decreases CRC-cell supernatant-triggered secretion of IL-10 and increases secretion of TNF-a, while the omega-6 polyunsaturated fatty acid (n-6 PUFA) arachidonic acid (AA) reduced TNF-a secretion. These changes in cytokine secretion upon incubation with DHA demonstrate a possible enhancing effect of n-3 PUFA on an anti-tumor immune response.