TTF1 and small cell lung carcinoma: In our prior research, we found that both POU2F3-expressing SCLC and LCNEC shared morphological and phenotypical similarities, including near-negative expression of TTF-1 and carcinoembryonic antigen (CEA) on immunohistochemistry, and exhibited improved recurrence-free survival (RFS) compared to their non-POU2F3-dominant counterparts [6].