neoplasia

Neoplasia literally means 'new growth' and describes clonal proliferation of cells that has escaped normal growth-regulating mechanisms. Unlike hyperplasia, neoplastic growth is monoclonal, irreversible, and autonomous—continuing even after the removal of the inciting stimulus. Neoplasms are classified as benign or malignant based on differentiation, growth rate, local invasion, and metastatic potential.

Pathophysiology involves accumulation of mutations in three key gene classes: (1) proto-oncogenes (gain-of-function mutations, e.g., RAS, MYC) that drive proliferation; (2) tumor suppressor genes (loss-of-function, e.g., TP53, RB1) that normally inhibit growth or promote apoptosis; and (3) DNA repair genes (e.g., BRCA1/2, mismatch repair genes) whose loss leads to genomic instability. The 'multi-hit' model of carcinogenesis explains why cancer typically requires multiple sequential mutations.

Hallmarks of malignant neoplasia (Hanahan & Weinberg) include sustained proliferative signaling, evasion of growth suppressors, resistance to apoptosis, replicative immortality (telomerase activation), angiogenesis induction, invasion and metastasis, reprogrammed energy metabolism (Warburg effect), and evasion of immune destruction.

Benign neoplasms are well-differentiated, slow-growing, encapsulated, and non-invasive (e.g., lipoma, leiomyoma), typically named with the suffix '-oma.' Malignant neoplasms show anaplasia, rapid growth, local invasion, and metastatic capability (e.g., carcinoma, sarcoma). Nomenclature depends on tissue origin: carcinomas arise from epithelium, sarcomas from mesenchymal tissue, and leukemias/lymphomas from hematopoietic cells.

Clinical relevance: Understanding neoplasia is essential for cancer screening, staging (TNM system), grading (differentiation), and treatment planning. Key risk factors include chemical carcinogens, radiation, oncogenic viruses (HPV, HBV, EBV), chronic inflammation, and hereditary syndromes (Li-Fraumeni, Lynch syndrome, familial adenomatous polyposis).