Fig. 4

Histopathological findings of the initial and second bronchoscopic biopsies. a: The initial bronchoscopic biopsy showed poorly differentiated carcinoma with many tumor infiltrating lymphocytes. b: On immunohistochemical staining, nearly all the tumor cells showed PD-L1 expression. c: The second bronchoscopic biopsy showed chronic inflammation with foamy histiocytic infiltration, suggesting tumor regression. d: The percutaneous lung needle biopsy revealed marked fibroelastosis without tumor cells, another histologic feature indicating tumor regression