TTF1 and neoplasm: It is hypothesized that TTF-1-negative tumors may be a factor in a poor response to PEM, as several reports have shown that PEM is less effective in smokers and that TTF-1 may reflect the effect of smoking [20], and it is also known that the expression of TTF-1 is strongly correlated with the degree of differentiation in tumor tissue [29] and that disease behavior similar to that of sqCC may be associated with a poorer prognosis in comparison to patients with nonsq NSCLC [30,31].