Cancer is a group of diseases in which abnormal cells divide uncontrollably and may invade nearby tissues or metastasize to distant organs, distinguishing malignant from benign neoplasms, with usage standardized by the World Health Organization and the National Cancer Institute. According to the WHO, cancer can arise in virtually any organ system and metastasis is the principal cause of cancer mortality. World Health Organization;
National Cancer Institute. (
who.int)
Epidemiology and burden
- –In 2022 an estimated 20 million new cancer cases and 9.7 million cancer deaths occurred globally, with approximately 53.5 million people alive within five years of a cancer diagnosis, highlighting substantial care and survivorship needs.
WHO/IARC. (
- –In the United States, about 2,001,140 new cancer cases and 611,720 cancer deaths were projected for 2024; overall cancer mortality has fallen by roughly 33% since 1991, reflecting tobacco reduction, screening, and improved treatments.
CA: A Cancer Journal for Clinicians;
American Cancer Society. (
- –The most commonly diagnosed cancers globally include female breast, lung, colorectal, prostate, stomach, and liver cancers, with patterns varying by region and income level.
Biology and pathophysiology
- –Malignant transformation involves genetic and epigenetic alterations that confer hallmark capabilities, including sustaining proliferative signaling, resisting cell death, inducing angiogenesis, enabling replicative immortality, activating invasion and metastasis, evading growth suppressors and immune destruction, and reprogramming cellular metabolism.
“Hallmarks of cancer: the next generation”. (
- –Conceptual updates emphasize phenotypic plasticity and disrupted differentiation as an emerging hallmark and recognize nonmutational epigenetic reprogramming and polymorphic microbiomes as enabling characteristics, alongside prominent roles for the tumor microenvironment.
American Association for Cancer Research. (
Etiology and risk factors
- –Major modifiable determinants include tobacco use, which causes cancers in numerous organs and accounts for the majority of lung cancer deaths, and secondhand smoke exposure.
CDC;
- –Alcoholic beverages are classified by the International Agency for Research on Cancer as carcinogenic to humans (Group 1), with sufficient evidence for cancers of the oral cavity, pharynx, larynx, esophagus (squamous), liver, female breast, and colorectum; risk decreases with reduction or cessation of intake.
IARC Handbooks FAQ. (
- –Excess body weight, physical inactivity, dietary patterns, and air pollution contribute materially to global cancer mortality; ultraviolet radiation drives most skin cancers.
- –Infections account for about 13% of new cancers worldwide, dominated by Helicobacter pylori, human papillomavirus (HPV), hepatitis B virus (HBV), and hepatitis C virus, with higher attributable fractions in low- and middle-income countries.
Cancer Atlas. (
Prevention and early detection
- –Vaccination prevents infection‑related cancers: CDC recommends routine HPV vaccination at ages 11–12 (can start at 9) with catch‑up through age 26 and shared decision‑making to 45; HPV vaccination prevents the majority of HPV‑attributable cancers.
- –Universal newborn HBV vaccination reduces chronic infection prevalence and hepatocellular carcinoma incidence, establishing the first cancer‑preventive vaccine in humans.
JNCI;
- –Screening recommendations evolve with evidence: the United States Preventive Services Task Force (USPSTF) in 2024 recommended biennial screening mammography for women aged 40–74 at average risk; USPSTF recommends colorectal cancer screening for adults 45–75 with multiple modality options; and annual low‑dose CT for adults 50–80 with ≥20 pack‑years who currently smoke or quit within 15 years.
USPSTF—Breast Cancer Screening;
AAFP summary of USPSTF—Lung Cancer. (
Diagnosis, classification, and staging
- –Histopathologic confirmation via biopsy remains the diagnostic gold standard, with pathology reports detailing tumor type, grade, margins, and other features that guide therapy.
NCI;
- –Imaging—including CT, MRI, ultrasound, and PET—supports detection, staging, treatment planning, and response assessment.
NCI;
- –The TNM system developed by the American Joint Committee on Cancer and the Union for International Cancer Control provides an internationally harmonized framework for anatomic staging, with the 8th edition widely implemented.
UICC;
ACS/AJCC. (
- –Biomarker testing enables precision medicine by identifying actionable genomic or protein alterations that inform targeted therapy and immunotherapy use in selected cancers.
Treatment modalities
- –Definitive and palliative cancer care draw on surgery, radiotherapy, systemic chemotherapy, endocrine therapy, targeted therapies (including monoclonal antibodies and small‑molecule inhibitors), and immunotherapies, often in multimodal sequences tailored by cancer type and stage.
- –Immune checkpoint inhibitors and cellular therapies exemplify immuno‑oncology’s impact; chimeric antigen receptor (CAR) T‑cell therapies are FDA‑approved for several hematologic malignancies, with characteristic risks such as cytokine‑release syndrome and neurotoxicity (ICANS) mitigated by established management protocols.
- –Increasingly, biomarker‑informed selection of targeted agents (for example, EGFR, ALK, BRAF, HER2, and others) and tumor‑agnostic indications (e.g., high MSI/TMB) illustrate the shift toward precision oncology.
Survivorship, equity, and systems
- –Survivorship care addresses late effects, secondary malignancy risk, and psychosocial needs in a growing population; in the United States there are more than 18 million cancer survivors.
- –Global access gaps persist in prevention, screening, diagnosis, treatment, and palliative care financing, with disproportionate burdens in underserved populations.
Historical notes
- –Descriptions of tumors date to ancient Egyptian and Greek sources; Hippocrates introduced the term karkinos (carcinoma) for tumors, reflecting early nosology of malignant disease.
Britannica. (
- –In the United States, the National Cancer Act of 1971 expanded the authority and resources of the National Cancer Institute, formalizing a coordinated National Cancer Program often referred to as the “war on cancer.”