What is Cancer? — General Information, Types, and Modern Approaches

Cancer is a heterogeneous collection of more than 200 distinct diseases unified by the hallmarks of malignancy: sustained proliferative signaling, evasion of growth suppressors, resistance to cell death, replicative immortality, induction of angiogenesis, and capacity for invasion and metastasis. The disease arises from accumulated genetic and epigenetic alterations that disrupt normal cellular homeostasis, with tumor heterogeneity driving treatment resistance and progression.

Cancer classification has evolved beyond traditional anatomic-histologic categorization to incorporate molecular subtyping based on driver mutations, gene expression profiles, and microenvironment characteristics. Major categories include carcinomas (epithelial origin, ~85%), sarcomas (mesenchymal origin), leukemias and lymphomas (hematologic), and central nervous system tumors. Modern classification integrates biomarkers such as HER2, EGFR, BRAF, BRCA, MSI, PD-L1, and tumor mutational burden to guide therapy selection.

The contemporary therapeutic armamentarium includes surgery, radiation therapy, cytotoxic chemotherapy, hormonal therapy, targeted molecular agents, immunotherapy (checkpoint inhibitors, CAR-T cells, bispecific antibodies), and emerging modalities such as antibody-drug conjugates and tumor-agnostic therapies. Treatment is increasingly personalized through comprehensive genomic profiling, liquid biopsy monitoring, and multidisciplinary tumor board decision-making to optimize outcomes.