CD274 and lung carcinoma: Given its canonical role in negatively regulating an activated immune system, the presence of PD-L1 may also indicate an attenuated, yet activated, immune microenvironment.41 Consequently, tumors with low or no expression of PD-L1 may tend to be resistant to anti-PD-1 and anti-PD-L1 treatments, as seen in breast and lung cancers which have historically demonstrated low PD-L1 expression.42,43 Despite this trend, the absence of PD-L1 does not necessarily preclude a positive response to such therapies, nor does its presence guarantee the treatment success.