The clinical significance of soluble PD-1 and PD-L1 in lung cancer

Soluble PD-1 and PD-L1 are detected in the serum and plasma of lung cancer patients. The significance of these soluble proteins as prognostic or predictive markers in lung cancer is uncertain. The testing methods used to detect soluble PD1/PD-L1 are variable with no agreement on a common definition of a positive test. The advantages of validating soluble PD1/PD-L1 relevance in lung cancer include easiness of obtaining blood samples for testing, serial measurements to assess response to treatments such as immunotherapy, and potentially early identification of cancer relapse in cases treated with curative intent. In this review, we present the available data published on soluble PD1 and PD-L1 in lung cancer.