MUC1 and pneumonitis: He complained of grade-2 exertional dyspnea on the mMRC (modified Medical Research Council) scale22 2 weeks after initiating durvalumab, and an area of consolidation was revealed in the right lung on his chest X-ray (red circle), concordant with a slight increase in his serum KL-6 level (405 U/mL) compared to baseline level (392 U/mL), suggesting pneumonitis.