Pulmonary carcinoids have low mutation rates. Mutational inactivation of TP53 and RB1 genes is seen in <5% of typical carcinoids and 20% of atypical carcinoids. In contrast, these mutations are seen in virtually 100% of pulmonary small cell carcinomas and large cell neuroendocrine carcinomas. The p16/retinoblastoma pathway is disrupted in about 20% of atypical carcinoids but is not seen in typical carcinoids. MEN1 Syndrome: Lung carcinoids occur in about 5% of patients with MEN1 syndrome carrying MEN1 germline mutations. MEN1 somatic mutations have been reported in about 40% of sporadic carcinoids. Most of these cases were atypical carcinoids. MEN1 mutations have not been recorded in small cell carcinoma or large cell neuroendocrine carcinoma. MEN1 gene is a tumor suppressor gene on chromosome 11q13. It codes for a 610 amino acid protein called Menin that localizes to the nucleus. Patients with MEN1 syndrome usually present with tumors of parathyroids, pancreas, or pituitary. Pulmonary carcinoids are uncommon in MEN1 syndrome as mentioned earlier.