Chapter 25: Cancer Biology

The text explains how tumorigenesis functions as an evolutionary process where natural selection favors cells with driver mutations that confer growth advantages, such as the ability to ignore contact inhibition, sustain proliferation without external signals, and utilize aerobic glycolysis (the Warburg effect) for energy even in the presence of oxygen,. A key focus is the genetic basis of cancer, distinguishing between proto-oncogenes, which become cancer-promoting oncogenes through gain-of-function mutations (like Ras or MYC), and tumor suppressor genes (like RB, p53, and APC), which require loss-of-function mutations in both alleles—often involving loss of heterozygosity (LOH)—to drive malignancy,. The summary details how these genetic alterations dysregulate critical signaling pathways, specifically the RTK/Ras/MAP kinase cascade, which stimulates cell division, and the cell cycle control machinery involving Cyclin D, CDK4/6, and the retinoblastoma protein (Rb) that regulates the restriction point,. It further explores how defects in DNA repair mechanisms, such as those seen in xeroderma pigmentosum or involving BRCA1/2, lead to genomic instability and hypermutation,. The multi-hit model of cancer progression is illustrated through colorectal cancer, showing how a sequential accumulation of mutations—starting with APC loss and followed by K-ras activation and p53 loss—transforms a benign polyp into a malignant carcinoma,. Additionally, the chapter covers the essential capabilities cancer cells must acquire, including inducing angiogenesis via VEGF to secure blood supply, undergoing the epithelial-to-mesenchymal transition (EMT) to invade tissues, and metastasizing to distant sites,. Finally, the text examines how tumors evade programmed cell death (apoptosis) by overexpressing anti-apoptotic proteins like Bcl2 or losing p53 function, and how they escape immune surveillance through immunoediting and checkpoint molecule expression (PD-L1), paving the way for modern immunotherapies like checkpoint inhibitors and chimeric antigen receptor (CAR) T cells,.