Karsinogenesis

Karsinogenesis, also called carcinogenesis, is the process by which normal cells accumulate genetic and epigenetic alterations that enable malignant transformation and tumor development. The term derives from Greek karkinos (crab) and genesis (origin). The concept encompasses the steps by which cells acquire traits that allow uncontrolled growth, resistance to cell death, and, in many cases, invasion of surrounding tissues.

Most cancer development is described as a multistep process beginning with initiation, followed by promotion and progression. Initiation involves irreversible genetic changes in a cell caused by mutagens or replication errors. Promotion entails the clonal expansion of initiated cells under growth-promoting signals. Progression includes acquisition of additional alterations that increase malignancy, enabling sustained growth, tissue invasion, and, eventually, metastasis to distant sites.

Carcinogenesis is influenced by a range of factors. Exogenous carcinogens include chemical agents (for example, components in tobacco smoke and aflatoxins) and physical factors (such as ionizing radiation and ultraviolet light). Oncogenic viruses, chronic inflammation, and immune suppression can contribute as well. Individual susceptibility is shaped by inherited genetic factors, age-related changes, lifestyle, and environmental exposure, with many cancers arising from the interaction of multiple influences over time.

Molecularly, carcinogenesis involves mutations in oncogenes and tumor suppressor genes, defects in DNA repair, and epigenetic changes that alter gene expression. Deregulated signaling pathways, evasion of apoptosis, genomic instability, and the acquisition of capabilities such as angiogenesis and tissue invasion drive progression from a localized lesion to invasive cancer.

Prevention and early detection rely on reducing exposure to carcinogens, vaccination against oncogenic viruses, screening programs, and lifestyle modifications. Ongoing research continues to elucidate mechanisms to inform targeted therapies and improved public health interventions.