neoplasm

Neoplasm is an abnormal mass of tissue resulting from uncontrolled, clonal cellular proliferation that persists after removal of the initiating stimulus. Neoplasms grow autonomously and are not part of normal tissue. They can be benign or malignant. The term neoplasm is distinct from a simple inflammatory or infectious swelling; not all enlargements are neoplasms, and benign neoplasms do not invade surrounding tissues or metastasize.

Neoplasms are classified by their tissue of origin: carcinomas arise from epithelial cells, sarcomas from mesenchymal tissues, hematologic neoplasms include leukemias and lymphomas, while glial and other tumors arise in the nervous system. Benign tumors, such as adenomas or lipomas, are typically well circumscribed, non-invasive, and slow-growing. Malignant tumors, including many carcinomas and sarcomas, invade adjacent structures and can spread (metastasize) to distant sites via blood or lymphatic systems.

Pathogenesis involves genetic and epigenetic alterations, including activation of oncogenes and inactivation of tumor suppressor genes, leading to deregulated cell proliferation, resistance to cell death, and other cancer hallmarks. Risk factors include tobacco use, obesity, infections (such as human papillomavirus and Helicobacter pylori), radiation, and certain chemical exposures; genetics and environment interact to influence risk and tumor behavior.

Diagnosis relies on clinical assessment, imaging, and tissue sampling with histopathology. Staging and grading help guide prognosis and treatment. Treatment modalities include surgery to remove localized tumors, radiation therapy, cytotoxic or targeted systemic therapies, immunotherapies, and hormonal therapies; palliative care remains important for advanced disease. Prognosis is highly variable and depends on histology, stage, and patient factors.

Terminology often uses -oma for benign neoplasms (e.g., lipoma, fibroma), with malignant epithelial tumors termed carcinomas and mesenchymal tumors termed sarcomas; lymphoma and leukemia describe hematologic malignancies. Some tumor names reflect historical usage rather than behavior (e.g., hepatocellular adenoma vs hepatocellular carcinoma).