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Oncology is the branch of medicine and biomedical science devoted to cancer: how it arises, how it is detected and classified, how it is treated, and how those treatments are tested. It is both a clinical specialty, practised by medical, surgical, radiation and pediatric oncologists and their colleagues in pathology and radiology, and a research discipline spanning cancer biology, genomics, epidemiology and clinical trials. (The name comes from the Greek onkos, meaning mass or bulk.) This guide explains what oncology covers and how its subspecialties divide the work, then adds the research-administration layer that generic overviews leave out: the National Cancer Institute (NCI), the cooperative trial networks, how trial phases and endpoints are defined, who funds cancer research, and typical training paths. It is educational, not medical advice.
What Is Oncology?
The National Cancer Institute describes cancer as a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body. Oncology is the discipline organized around that problem. Cancer is not one disease but a large family of them, and the field classifies them in several overlapping ways, most commonly by tissue of origin:
- Carcinomas arise from epithelial cells that cover body surfaces and line organs, and include most breast, colon, prostate and lung cancers.
- Sarcomas arise in bone and soft tissues such as muscle, fat and blood vessels.
- Leukemias arise in blood-forming tissue in the bone marrow, and lymphomas in lymphocytes. Multiple myeloma arises from plasma cells. These blood cancers overlap with hematology.
- Melanoma arises from pigment-producing melanocytes, and brain and spinal cord tumors are named by cell type and location in the nervous system.
Compared with normal cells, cancer cells characteristically grow without external growth signals, ignore signals to stop dividing or die, invade nearby tissue, recruit blood vessels, evade the immune system and accumulate chromosomal abnormalities. Metastasis, the spread of cancer cells through blood or lymph to form secondary tumors at distant sites, is what makes many cancers hard to cure and is a central focus of both treatment and research.
The Clinical Subspecialties
Cancer care is multidisciplinary by design. Most patients see several kinds of oncologist, often coordinated through a tumor board where specialists review a case together.
Medical Oncology
Medical oncologists treat cancer with drugs given systemically: cytotoxic chemotherapy, hormone therapy, targeted therapy aimed at specific molecular alterations, and immunotherapy that engages the immune system. They also coordinate overall care, manage side effects and increasingly choose treatments based on tumor molecular testing. Because most new cancer drugs are developed through clinical trials, medical oncologists are often the investigators on those studies.
Surgical Oncology
Surgical oncologists remove tumors and the tissue around them, perform biopsies that establish a diagnosis, assess lymph nodes and treat selected metastatic disease. Surgery is frequently combined with drug or radiation treatment given before or after the operation. Surgical trials raise their own methodological problems, since blinding and standardization are harder than in drug studies.
Radiation Oncology
Radiation oncologists use ionizing radiation, delivered from external beams or placed internally, to destroy cancer cells while sparing surrounding tissue, working closely with medical physicists and dosimetrists. See What Is Radiation Oncology? for the full treatment of that specialty and Radiology vs Radiation Oncology for a frequent point of confusion.
Other Oncology Subspecialties
- Pediatric oncology treats cancers of children and adolescents, which differ biologically from adult cancers and are largely studied through coordinated national trials.
- Gynecologic oncology and other organ-specific oncology practices combine surgical and medical expertise for one disease site.
- Hematologic oncology treats leukemias, lymphomas and myeloma, and is often a joint field with hematology.
- Pathology and diagnostic imaging are not oncology subspecialties as such, but cancer diagnosis and staging depend on them; see What Is Medical Imaging?
- Palliative care, survivorship and cancer prevention address symptoms, long-term effects of treatment and risk reduction across the cancer continuum.
Cancer Biology and Translational Research
Behind the clinic sits a large basic and translational research enterprise. Cancer biology studies how mutations and other changes in DNA, gene regulation and the surrounding tissue environment turn normal cells into malignant ones. Genomics has transformed the field by cataloguing the alterations in tumors; The Cancer Genome Atlas (TCGA) is one widely used public resource. Immunology underpins immunotherapy, and pharmacology underpins the design and dosing of anticancer drugs.
“Translational research” is the work of moving a laboratory finding toward patients: identifying a target, building preclinical models, and then testing the agent in humans. Preclinical models include cell lines, genetically engineered animals and patient-derived xenografts; the last of these raise particular questions about drift and welfare, covered in Patient-Derived Xenograft Models. Epidemiology identifies risk factors and patterns of incidence and survival, and biostatistics supplies the survival analysis and trial-design methods the whole field depends on.
The National Cancer Institute and NCI-Designated Cancer Centers
The NCI is the principal U.S. federal agency for cancer research, and its authority was greatly expanded by the National Cancer Act of 1971, signed by President Richard Nixon on December 23, 1971. According to NCI, the act gave the NCI director broad authority to plan and develop a National Cancer Program, including authority to create cancer centers and training programs, and set up a “professional judgment budget” in which the NCI director submits annual budget proposals directly to the President and Congress. It also created the National Cancer Advisory Board and the President’s Cancer Panel.
NCI also designates cancer centers. Its website currently lists 74 NCI-designated cancer centers across 37 states and the District of Columbia, in three categories: clinical cancer centers, comprehensive cancer centers and basic laboratory cancer centers. Most are affiliated with university medical centers. For researchers, designation matters because it signals institutional infrastructure and shapes how a center organizes shared resources and trial support. Counts change with new designations, so check NCI for the current figure.
How Cancer Research Is Funded
Federal funding, led by the NCI within the National Institutes of Health, is a major source of cancer research support in the United States, supplemented by other federal programs, state programs, industry sponsors and charitable organizations. The mechanics of NCI grants, including paylines and how institute-specific funding decisions differ, are covered in NCI Funding, and the wider landscape of public, private and international sponsors is in Cancer Research Funding: A Landscape Overview. For funding-line context across institutes, see NIH paylines for FY2026.
Early-career researchers commonly use career-development mechanisms such as the K99/R00 Pathway to Independence Award, and nonprofit programs such as the Damon Runyon Cancer Research Foundation fellowship and career awards. Large cooperative trials are often funded through cooperative-agreement mechanisms in which the funder remains substantially involved; see the U01 NIH cooperative agreement entry. Federal grants carry data-sharing obligations, summarized in NIH Data Management and Sharing Plan. All of this sits within research administration, the compliance and grants-management layer that makes funded science possible.
Clinical Trials, Phases and Endpoints
New cancer treatments reach patients through staged clinical trials. NCI describes the phases as follows, with typical sizes that vary by study:
- Phase 1 tests whether a new treatment is safe, what its side effects are, whether people can tolerate it and what the highest tolerable dose is. NCI gives a typical size of around 15 to 30 participants. Dose-finding designs are compared in 3+3 Design vs. Continual Reassessment Method.
- Phase 2 asks whether the treatment works against the cancer, for example by shrinking tumors or slowing growth, while continuing to watch safety. NCI gives a typical size of 50 to 100 participants. Expansion cohorts are a common feature; see Expansion Cohort Trial Design in Oncology.
- Phase 3 compares the new treatment with the current standard to see which works better and compares side effects. NCI gives a range from 100 to several thousand participants. See Non-Inferiority vs Superiority Trial Design for how these comparisons are framed.
- Phase 4 looks at long-term safety and effectiveness after FDA approval, in large and diverse populations.
For the general model of how phases work across medicine, see Clinical Trial Phases. Oncology trials differ from most other fields in what they measure. Tumor response is commonly assessed on imaging with standardized criteria, and longer-term outcomes include time-to-event measures such as how long patients live or remain free of progression. Surrogate and composite measures are common, which makes it important to understand what each endpoint does and does not show; the composite endpoint and accelerated approval entries explain two related concepts. The full treatment of RECIST and the trial network is in What Makes Oncology Clinical Trials Different: RECIST, Endpoints, and the NCTN. FDA oncology-specific programs are covered in Project Optimus and Real-Time Oncology Review. All trials rest on informed consent and independent ethics review.
The NCI National Clinical Trials Network (NCTN)
Much publicly funded cancer trial research in the United States and Canada runs through the NCI National Clinical Trials Network, which NCI describes as a collection of organizations and clinicians that coordinates and supports cancer clinical trials at more than 2,200 sites across the United States, Canada and internationally. It comprises five U.S. network groups: the Alliance for Clinical Trials in Oncology, ECOG-ACRIN Cancer Research Group, NRG Oncology, SWOG and the Children’s Oncology Group, plus the Canadian Cancer Trials Group. NCI also lists 32 Lead Academic Participating Sites alongside community hospitals and medical centers. The term “cooperative groups” is still widely used in the field for networks of this kind. Trial billing and regulatory support is centralized through NCI’s Cancer Trials Support Unit; see CTSU: Billing and Regulatory Support.
Common Research Methods and Tools
- Tumor sequencing and biomarker testing to identify molecular alterations that guide targeted treatment and trial eligibility.
- Preclinical models, including cell lines, organoids, engineered animals and patient-derived xenografts.
- Imaging, used for staging, response assessment and increasingly for quantitative biomarkers.
- Population studies and registries that track incidence, survival and outcomes at scale.
- Adaptive and master-protocol trial designs that test several treatments or biomarkers under a common structure.
- Survival statistics, such as Kaplan-Meier estimation and hazard ratios, central to reporting time-to-event outcomes.
A Brief History
Only a few milestones are stated here, each taken from the organizations’ own descriptions. The American Association for Cancer Research was established on May 7, 1907, in Washington, D.C. The American Society of Clinical Oncology was established in 1964 by a small group of founders that included Jane C. Wright. The National Cancer Act of 1971 expanded the NCI’s authority and funding model, as described above. Modern oncology’s later history is largely the story of molecular profiling, targeted drugs, immunotherapy and ever more structured trial networks.
Career and Training Pathways
Training varies by country, so verify requirements with the relevant licensing and certifying bodies. In the United States, clinical oncologists typically complete medical school, a residency (in internal medicine for medical oncology, in surgery for surgical oncology, or in radiation oncology) and, for medical and surgical oncology, additional fellowship training. Physician-scientists often add research training supported by career-development awards. Laboratory-based cancer researchers typically hold a PhD and complete postdoctoral training, while clinical research professionals, biostatisticians, data managers, regulatory staff and research administrators support trials and grants. Cancer centers and trial networks employ many of these roles.
Societies and Journals
Two societies dominate the field’s professional life. The American Society of Clinical Oncology (ASCO) represents physicians across oncology specialties and publishes the Journal of Clinical Oncology along with several related JCO titles; its grants arm, the Conquer Cancer Foundation, funds cancer research grants. The American Association for Cancer Research (AACR) states a mission to prevent and cure cancer through research, education, communication, collaboration, science policy and advocacy, and funding. It publishes ten peer-reviewed journals, including Cancer Discovery, Cancer Research, Clinical Cancer Research and Molecular Cancer Therapeutics. Journal prestige metrics for two of these are covered in the Cancer Discovery and Cancer Research impact factor entries.
Frequently Asked Questions
What does an oncologist do?
An oncologist is a physician who diagnoses and treats cancer. Medical oncologists use drug-based treatments, surgical oncologists operate, and radiation oncologists use radiation, usually as members of a team.
What is the difference between oncology and hematology?
Hematology covers blood and blood-forming tissue, including non-cancerous conditions. Oncology covers cancer in all tissues. The two overlap in leukemia, lymphoma and myeloma, and many physicians train in both. See What Is Hematology?
What is the NCTN?
The NCI National Clinical Trials Network is the NCI-supported network of groups and sites that conducts cancer trials in the United States, Canada and elsewhere. See the section above and the RECIST and NCTN guide.
How are oncology clinical trials different from other trials?
They rely heavily on imaging-based response criteria, time-to-event endpoints and dose-finding designs built around toxicity, and they are often run through cooperative networks. The dedicated guide linked above covers this in depth.
Who funds cancer research?
The NCI is a leading federal funder in the United States, alongside other agencies, industry and charitable foundations. See NCI Funding and Cancer Research Funding.
Is this page medical advice?
No. It describes a field and its research infrastructure. Anyone with questions about a diagnosis or treatment should consult a qualified clinician.
