title: Small cell lung cancer: significance of RB alterations and TTF-1 expression in its carcinogenesis, phenotype, and biology.
abstract: Small cell lung cancer (SCLC) exhibits highly aggressive behavior and has a poor prognosis. While numerous investigations have been carried out, the exact mechanism of its carcinogenesis and aggressiveness is still unclear. SCLC is categorized as a neuroendocrine neoplasia and has a genetic profile characterized by universal alterations of the RB and TP53 genes. Epidemiological studies indicate the majority of SCLCs to be caused by smoking and the TP53 mutational pattern to be consistent with that evoked by smoke carcinogens; however, there is no direct evidence that such carcinogens induce alterations to RB in SCLC. While the importance of these alterations in the carcinogenesis of SCLC is strongly suggested, the exact molecular mechanism has been only little elucidated. SCLC cells almost always express mammalian achaete-scute homolog-1 (MASH1) and thyroid transcription factor-1 (TTF-1). MASH1 plays a critical role in neuroendocrine differentiation. TTF-1 is a characteristic marker of distal airway cells and pulmonary adenocarcinomas, but is also expressed in extrapulmonary neuroendocrine cancers. Thus, TTF-1 may well play a significant role in the development of neuroendocrine cancers. Recent studies indicate that the airway stem cell is committed to the neuroendocrine lineage through MASH1 and Notch signaling and that only RB-deleted neuroendocrine cells selectively proliferate in response to E2F3, eventually undergoing transformation to neuroendocrine cancer cells, probably in concert with TP53 gene aberrations. Thus, alterations of both the RB and TP53 genes are central to the carcinogenesis of SCLC, while many other factors including MASH1 and TTF-1 contribute to the development and biological behavior of SCLC.
authors.affiliation: Department of Pathology, Graduate School of Medicine, Yokohama City University, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan. pathola@med.yokohama-cu.ac.jp
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kitamura
authors.forename: Takuya
authors.initials: T
authors.lastname: Yazawa
authors.forename: Hanako
authors.initials: H
authors.lastname: Sato
authors.forename: Koji
authors.initials: K
authors.lastname: Okudela
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Shimoyamada
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics; D018450:Disease Progression; D050687:E2F1 Transcription Factor / Q000235:genetics; D052138:Genes, Neoplasm; D016161:Genes, Retinoblastoma; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics*; D009361:Neoplasm Invasiveness; D009687:Nuclear Proteins / Q000235:genetics*; D010641:Phenotype; D055752:Small Cell Lung Carcinoma / Q000235:genetics*; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000235:genetics*; D015533:Transcriptional Activation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D050687:E2F1 Transcription Factor; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; C065500:ASCL1 protein, human; C493753:E2F1 protein, human; C000614412:NKX2-1 protein, human