YAP1 and small cell lung carcinoma: The non-neuroendocrine subtype weakly expresses both ASCL1 and NEUROD1, while YAP1, a co-transcription factor activated by the HIPPO signal pathway, and POU2F3, a transcription factor expressed by rare chemosensory cells called “tuft cells,” are both strongly expressed by some variant types of SCLC [24,25].