The baseline circulating immunophenotype characteristics associate with PD(L)-1 targeted treatment response, irae onset, and prognosis.

More promising, effective, and less-invasive biomarkers for PD(L)-1 targeted responses, immune-related adverse events (irAEs), and prognosis are being explored. We conducted a single-center retrospective study in pan-cancer patients with anti-PD(L)-1 monotherapy. Observational endpoints included treatment response, prognosis, and irAEs. Peripheral blood immunophenotypes were analyzed by Flow Cytometry. 104 patients were enrolled. Higher pretreatment percentages of CD3CD4 Th cells were associated with both responses (HR: 6.170, P = 0.034) and prognosis (HR: 1.930, P = 0.022). The higher baseline percentage of CD16CD56 NK cells was positively correlated with response (HR: 3.730, P = 0.050) and negatively related to irAEs (HR: 0.460, P = 0.012). Decreased pretreatment CD3 T cell counts were related to more irAEs (HR: 0.970, P = 0.026), while the percentage of CD3 T cells was negatively associated with prognosis (HR: 1.930, P = 0.022). The higher baseline cell counts of CD3CD8 CTL, CD19 B, and the percentage of CD19 B cells might be related to more irAEs (P < 0.05). Significant correlation between duration of treatment (DOT) and prognosis, irAE and outcome was also confirmed (P < 0.0001). Our findings confirmed multiple baseline circulating immunophenotype characteristics were related to PD(L)-1 targeted response, irAE onset, and prognosis.