Alternative definition : KEGG: Small cell lung carcinoma (SCLC) is a highly aggressive neoplasm, which accounts
for approximately 20% of all lung cancer cases. Molecular mechanisms altered in SCLC
include induced expression of oncogene, MYC, and loss of tumor suppressor genes, such
as p53, PTEN, RB, and FHIT. The overexpression of MYC proteins in SCLC is largely
a result of gene amplification. Such overexpression leads to more rapid proliferation
and loss of terminal differentiation. Mutation or deletion of p53 or PTEN can lead
to more rapid proliferation and reduced apoptosis. The retinoblastoma gene RB1 encodes
a nuclear phosphoprotein that helps to regulate cell-cycle progression. The fragile
histidine triad gene FHIT encodes the enzyme diadenosine triphosphate hydrolase, which
is thought to have an indirect role in proapoptosis and cell-cycle control.;