HTR1B and cancer: In pan-cancer, high expression of HTR1B/1F/2B/4/7 was positively correlated with the expression of PD-1, PD-L1, and CTLA4 while the expression of HTR1A was negatively correlated with the expression of PD-1, PD-L1, and CTLA4 in GLB, LGG, SARC, OV, and PAAD (Figure 6B).