PI3K/AKT/mTOR pathway in pulmonary carcinoid tumours.

The present study examined the expression of mammalian target of rapamycin (mTOR) and mutations in the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway in 54 patients with typical carcinoid tumours (TC) or atypical carcinoid tumours (AC). In total, 54 bronchopulmonary neuroendocrine tumour (NET) surgical specimens, consisting of 17 TC, 8 AC, 17 large-cell neuroendocrine carcinoma (LCNEC), and 12 small-cell lung carcinoma (SCLC) samples, were tested for mTOR by immunohistochemistry, and 104 exon sites were tested in the PI3K/AKT/mTOR pathway by nested polymerase chain reaction. It was found that the positive rates for mTOR expression in TC/AC and LCNEC/SCLC were 60 (15/25) and 55.2% (16/29), respectively. In total, 4 missense mutations were found in 3 patients with TC/AC, including mutations in exon 48 of mTOR (c.6667C>T), exon 21 of tuberous sclerosis complex (TSC) 1 (c.2765G>A), and exons 12 (c.1265C>T) and 19 (c.2148C>T) of TSC2. To the best of our knowledge, mutations in exon 48 of mTOR and exon 21 of TSC1 have not been previously reported. Tissues from patients with single mutations exhibited strong positive mTOR immunohistochemical staining, and tissues from patients with double mutations were weakly positive. The same mutations were not observed in SCLC or LCNEC. In conclusion, gene mutations were observed and an association between the gene mutations and mTOR expression were indicated in the PI3K/AKT/mTOR pathway in TC/AC tumours. Those mutations may be driver genes and treatment targets.