PDCD1 and lung carcinoma: On the basis of our preclinical findings that low-dose apatinib optimizes tumor microenvironment and potentiates antitumor effect of PD-1 and PD-L1 blockade in lung cancer, we conducted a multicohort, phase 1b and 2 study to evaluate the chemo-free combination of camrelizumab and apatinib.29