This study investigated the structure and expression of the retinoblastoma (Rb) gene in small cell lung cancer (SCLC) and other lung cancers. The Rb gene is located on chromosome 13q14 and is associated with retinoblastoma, a childhood tumor. The study found structural abnormalities in the Rb gene in 13% of primary SCLC tumors, 18% of SCLC cell lines, and 25% of pulmonary carcinoid lines. These abnormalities were not detected in other major types of lung cancer. Rb mRNA expression was absent in 60% of SCLC lines and 75% of pulmonary carcinoid lines, including those with DNA abnormalities. In contrast, Rb transcripts were found in 90% of non-SCLC lung cancer lines and in normal human lung tissue. These findings suggest that the Rb gene may be involved in the pathogenesis of SCLC and pulmonary carcinoids, which are both neuroendocrine tumors. The study also examined the karyotypes of 11 SCLC lines and found abnormalities involving the 13q14 region in three of them. These findings support the idea that the Rb gene may be inactivated in these tumors. The presence of Rb gene abnormalities in SCLC and pulmonary carcinoids suggests that these tumors may share a common pathogenic mechanism. The study also found that the Rb gene is frequently deleted in SCLC and other tumors, indicating that it may play a role in the development of these malignancies. The results suggest that the Rb gene may be involved in the pathogenesis of a common adult malignancy, and that mutations in both alleles of the Rb gene may occur as somatic events in SCLC. The study highlights the importance of the Rb gene in the development of lung cancers and suggests that it may play a role in the malignant transformation of various tissues beyond the retina.This study investigated the structure and expression of the retinoblastoma (Rb) gene in small cell lung cancer (SCLC) and other lung cancers. The Rb gene is located on chromosome 13q14 and is associated with retinoblastoma, a childhood tumor. The study found structural abnormalities in the Rb gene in 13% of primary SCLC tumors, 18% of SCLC cell lines, and 25% of pulmonary carcinoid lines. These abnormalities were not detected in other major types of lung cancer. Rb mRNA expression was absent in 60% of SCLC lines and 75% of pulmonary carcinoid lines, including those with DNA abnormalities. In contrast, Rb transcripts were found in 90% of non-SCLC lung cancer lines and in normal human lung tissue. These findings suggest that the Rb gene may be involved in the pathogenesis of SCLC and pulmonary carcinoids, which are both neuroendocrine tumors. The study also examined the karyotypes of 11 SCLC lines and found abnormalities involving the 13q14 region in three of them. These findings support the idea that the Rb gene may be inactivated in these tumors. The presence of Rb gene abnormalities in SCLC and pulmonary carcinoids suggests that these tumors may share a common pathogenic mechanism. The study also found that the Rb gene is frequently deleted in SCLC and other tumors, indicating that it may play a role in the development of these malignancies. The results suggest that the Rb gene may be involved in the pathogenesis of a common adult malignancy, and that mutations in both alleles of the Rb gene may occur as somatic events in SCLC. The study highlights the importance of the Rb gene in the development of lung cancers and suggests that it may play a role in the malignant transformation of various tissues beyond the retina.