POU2F3 and small cell lung carcinoma: The nmf1 subtype corresponds to SCLC-A/N with high neuroendocrine scores and frequent ASCL1/NEUROD1 co-expression; nmf3 displays the highest epithelial-mesenchymal transition (EMT) score, correlating with metastasis and chemoresistance; and nmf4 (SCLC-P) shows exclusive POU2F3 expression and MYC-driven metabolic reprogramming, particularly purine synthesis dependency.