CD274 and malignant mesothelioma: IHC is employed in lung cancer for various purposes, such as (i) distinguishing between ADC and SqCC; (ii) detecting neuroendocrine markers; (iii) identifying driver genetic alterations (ALK, ROS1, and EGFR); (iv) assessing PD-L1 (CD274) expression; (v) discriminating between lung carcinoma and malignant mesothelioma; and (vi) diagnosing NUT carcinoma [108].