Clinical significance of soluble forms of immune checkpoint molecules in advanced esophageal cancer.

Immune checkpoint molecules are expressed on cancer cells and regulate tumor immunity by binding to ligands on immune cells. Although soluble forms of immune checkpoint molecules have been detected in the blood of patients with some types of tumors, their roles have not been fully elucidated. Soluble PD-L1, PD-1, CD155, LAG3, and CD226 (sPD-L1, sPD-1, sCD155, sLAG3, and sCD226, respectively) were measured in the sera of 47 patients with advanced esophageal cancer and compared with those of 24 control subjects. Pretreatment levels of sPD-1 and sCD155 were significantly higher in the patients with cancer than in the control subjects (P = 0.023, P = 0.001). The sPD-1 levels tended to be higher in the patients with lymph node metastasis, a large tumor diameter, and higher levels of serum SCC antigen (P = 0.150, P = 0.189, and P = 0.078, respectively). However, higher levels of sCD155 were associated with a better response to chemotherapy and favorable overall survival (P = 0.111 and P = 0.068, respectively). After 2 courses of chemotherapy, the levels of sCD155 and sCD226 were significantly increased (P < 0.001 and P = 0.002, respectively). Moreover, the increase in sCD226 during chemotherapy was associated with poor treatment response (P = 0.019). sPD-1 levels are possibly dependent on the tumor aggressiveness of the esophageal cancer. Furthermore, the pretreatment levels of sCD155 and kinetic change of sCD226 after chemotherapy may be used as biomarkers of the treatment response and prognosis in patients with esophageal cancer.