The differences in the PIK3CA gene mutational status between LCNECs and ACs or SCLC observed in our study may suggest that a different signalling pathway such as the MAPK pathway or other receptor tyrosine kinases (RTKs), but not PI3K, may play a key role in the tumourigenesis of the former type of BP-NETs. Here, PIK3CA is linked to small cell lung carcinoma.