What Is Oncology?

The Field of Medicine That Addresses Cancer

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Oncology is the field of medicine that deal with the diagnosis, treatment, prevention, and early detection of cancer. Oncologists, in turn, are physicians who treat people with cancer. Cancer has been present through the ages, and is currently the second leading cause of death in the United States.

Fortunately, treatments are improving, and an understanding of cancer on the molecular level has led to improvements in survival as well. We will look at some of the types of oncology professionals, common (and uncommon symptoms), and how it may be diagnosed and treated.

hands holding different cancer ribbons for different areas of oncology

Andrei Orlov /  Istockphoto.com / Stock


While the term "Onco" means mass, and "logy" means study, not all cancers cause a mass. There are hundreds of types of cancer that may arise from epithelial cells (such as breast ducts and airways in the lungs), connective tissue (such as sarcomas), or blood cells (such as leukemias and lymphomas).

Even cancers that arise in the same tissue (say, the lungs) differ on a molecular level, such that no two cancers are alike. Unlike benign conditions or tumors, there are several factors that make a cancer cell a cancer cell.

Cancer is caused by the uncontrolled growth and reproduction of a cell that is initiated by a series of mutations in a normal cell. There are hallmarks of cancer that differentiate it from benign conditions. In addition to uncontrolled growth, cancer cells work to create new blood vessels to supply their growth, resist death, and much more.

Cancer cells often lack sticky substances known as adhesion molecules that keep the cells in place. This allows the cells to spread (metastasize) to other regions of the body. It is the metastasis of tumors, in fact, that is responsible for the majority of deaths from cancer (at least solid tumors).

Incidence and Prevalence

Currently ranked as the second leading cause of death, it's thought that cancer will affect roughly 1 in 2 men and 1 in 3 women during their lifetime. Survival rates are improving, yet as more people live with cancer, the prevalence of cancer survivors (and the need for oncology care) will increase.

As of January of 2019, there were 16.9 million cancer survivors living in the United States, with that number expected to increase to 22.1 million by 2030.


Researchers have noted evidence of cancerous (malignant) tumors in animals even before people inhabited the earth. The earliest written description of the disease was in 3000 BC, but evidence has been noted further back in fossils and mummies.

The Greeks were primarily responsible for the first treatment approaches to the disease, which included the use of a combination of medicine and art.


There are many types of cancer as well as health professionals who treat the disease.


There are three primary types of oncologists or physicians who treat people with cancer. These include:

  • Medical oncologists treat people with medications such as chemotherapy, targeted therapy, hormonal therapy, and immunotherapy.
  • Surgical oncologists perform surgeries to remove malignant tumors.
  • Radiation oncologists use radiation to treat cancer.

Oncologists/hematologists treat not only people who have cancer but also people who are coping with benign blood-based diseases such as anemia.

Oncologists may also be referred to as either community oncologists; oncologists who work at cancer centers in the community and generally treat all types of cancer, and academic oncologists; physicians who work at the larger cancer centers and often specialize in one type (or one subtype) of cancer.

There are also many subspecialties of oncology. Some of these include:

  • Pediatric oncologists, treating children with cancer
  • Adolescent and young adult oncology
  • Gynecologic oncologists, treating tumors such as ovarian cancer, cervical cancer, and uterine cancer
  • Neurooncologists, addressing cancers such as brain cancer and metastases to the brain from other tumors, as well as central or peripheral nervous system side effects of treatment, such as peripheral neuropathy or cognitive dysfunction
  • Sarcoma specialists
  • Gastrointestinal oncologists, who treat tumors of the colon, GIST tumors, etc.
  • Psychooncologists, addressing the emotional and psychological aspects of living with cancer
  • Precision oncologists, who address the molecular characteristics (what's happening with a tumor at a genomic level) to guide treatments personalized to a tumor
  • Integrative oncologists, who look at ways to integrate conventional medicine with alternative therapies (such as yoga and much more) that may improve a person's quality of life while living with cancer
  • Immunotherapy-oncologists
  • Oncology rehabilitation specialists
  • Preventive oncologists
  • Urologists, who treat prostate cancer
  • Survivorship specialists, as with more people surviving cancer, often with long term side effects, issues surrounding survivorship have developed into a field of its own.

Oncology can also be broken down by focus into:

  • Clinical oncology that addresses people living with cancer
  • Epidemiology that looks into risk factors as well as trends in cancer diagnoses
  • Cancer biology that looks at the biology behind the growth of tumors to design new treatments

The Oncology Team

The treatment of cancer increasingly requires a "multidisciplinary" approach, and there are many types of physicians as well as other healthcare professionals who may be part of your treatment team. This team may include:

  • An oncologist as noted above
  • Diagnostic radiologists, who use imaging techniques to detect and monitor cancer
  • Pathologists, physicians who diagnose cancer by looking at a tumor (or blood/bone marrow sample) under the microscope and perform studies to determine the molecular characteristics of a tumor. They have become more active as part of the oncology team in recent years with the advent of precision medicine.
  • Oncology nurses
  • Oncology social workers
  • Palliative care specialists who address the symptoms and side effects related to cancer. Palliative care is not the same as hospice, and may be recommended even for people with very curable tumors.
  • Oncology nutritionists
  • Supportive specialties such as physical therapy or speech pathology
  • Rehabilitation specialists
  • Patient navigators

Types of Cancer

Cancer can affect nearly any type of tissue in the body, but is much more common in some regions than others. The types of cancer can be broken down in many ways, but it can be helpful to look at three basic categories.

  • Carcinomas: These are cancers that begin in epithelial cells that line the surface of the body (skin) or body cavities (such as breast ducts or airways). They make up the largest group of cancers.
  • Sarcomas: These are cancers of connective tissue such as bone, blood vessels, cartilage, nerves, and more.
  • Blood-based cancers: These include leukemias, lymphomas, and multiple myeloma.

Oncology Terminology

For those who are diagnosed with cancer, learning about their disease can feel like learning a foreign language. One term that confuses many people is "invasive cancer." Having invasive cancer does not mean that cancer has spread or metastasized, but only that a tumor has the potential to spread.

Many epithelial tumors begin as an area of abnormal tissue (dysplasia). This can progress to carcinoma-in-situ or CIN. With CIN, the cells are still contained by something called the basement membrane, and if removed, are in theory 100% curable.

When cells spread beyond the basement membrane, the abnormality is then considered invasive cancer. Even very small tumors, such as a stage IA breast cancer, is thus referred to as "invasive" cancer.

Unlike carcinomas, sarcomas do not have this precancerous stage, and therefore screening techniques for early detection cannot detect these cancers at a carcinoma-in-situ stage.


The symptoms of cancer can range from mild (or not present at all) to life-threatening. Some symptoms tend to be specific for certain cancers, whereas others may be present with many types of cancer.

Signs and Symptoms of Cancer

Some signs and symptoms that may be concerning include:

  • Enlarged lymph nodes, whether present in the neck, just above the collarbone, in the armpits, or the groin
  • Lumps, for example, in the breast or testicles
  • Pain nearly anywhere, such as headaches, abdominal pain, or back pain
  • Bleeding, such as gastrointestinal tract bleeding, coughing up blood, or nosebleeds
  • Skin changes, such as a changing or new mole or a sore that is not healing
  • Abdominal symptoms such as abdominal bloating, nausea and/or vomiting, jaundice (a yellowish discoloration of the skin), or any change in bowel habits
  • Neurological symptoms such as headaches, visual changes, speech changes, or the new onset of seizures
  • Respiratory symptoms, such as a persistent cough, shortness of breath, or recurrent respiratory infections
  • Hoarseness

General Symptoms of Cancer

The symptoms of cancer may be nonspecific and associated with a wide range of cancers. Some of these are more common with advanced or metastatic cancers, though they may occur even before other symptoms with early stage tumors.

General symptoms may include:

  • Fatigue: Cancer fatigue tends to be worse than the feeling you have when you don't get enough sleep. It may be present even after a good night's rest or a cup of coffee. Many people are hesitant to talk to their healthcare provider about fatigue, but it's important to do so.
  • Night sweats: Hot flashes are common, especially in women near the time of menopause, but drenching night sweats are always something to discuss with your healthcare provider.
  • Persistent fever without a known reason: If a fever can't be explained by an obvious infection (fever of unknown origin), you should see your healthcare provider. A fever as a sign of cancer is most common with blood-related cancers such as lymphomas.
  • Unexplained weight loss: Unintentional weight loss can be a sign of cancer. A loss of 5% of body mass over a six-month period (such as a 200-pound person losing 10 pounds) without trying can be a sign of cancer. Cachexia, a combination of weight loss and muscle wasting, is common with late stage cancers.

Surprising Symptoms of Cancer

In addition to the above symptoms, there are several that might not initially raise a person's suspicion of cancer. This is not a complete list but is a good reminder that people should make an important to see their healthcare provider with any concerns about their health. Some surprising symptoms of cancer include:

  • Nail clubbing: The fingernails begin to look like upside-down spoons. There are a number of causes of clubbing and it is sometimes a normal variation, but the most common cause is lung cancer.
  • Depression: It's not surprising that a person would be depressed after a diagnosis of cancer, but sometimes depression is the first symptom. With lung cancer, the cancer itself may cause inflammation that causes an inflammatory-based depression.
  • Facial swelling: This is seen with superior vena cava syndrome.
  • A droopy eyelid: This is seen in Horner's syndrome, a type of paraneoplastic syndrome.
  • Muscle cramps: This is due to an increased calcium level (hypercalcemia of malignancy) in the blood.
  • Itching: Localized or generalized itching can sometimes be a symptom of cancer.
  • Blood clots: Deep vein thromboses and sometimes pulmonary emboli are not only common but also sometimes the first sign of cancer.


We have come a long way since Hippocrates first opposed superstitions surrounding cancer and attributed the disease, instead, to natural causes. At the time, however, it was thought to be due to an imbalance of blood, mucus, bile, and other body fluids.

We now know that cancer arises (oncogenesis) after a series of mutations in a normal cell leads to the uncontrolled growth of a tumor. Most often, this includes mutations in both oncogenes (genes that promote the growth of cells) and tumor suppressor genes (genes that code for proteins that repair damaged cells or eliminate them so they can't go on to become a cancer).

Mutations can arise due to exposures to carcinogens in the environment or due to byproducts of the normal metabolism of cells. Hereditary mutations (such as BRCA mutations) can also predispose a person to develop cancer. It is actually quite difficult for a normal cell to become a cancer cell, and there are many checks and balances in the body to prevent this.

It's important to distinguish hereditary (germline) mutations from acquired (somatic) mutations. Most mutations responsible for cancer arise after birth. The fact that these mutations accumulate over time is the reason why cancer becomes more common as we age. In some cases, however, a combination of hereditary and acquired mutations is responsible.

Epigenetics, or non-permanent changes to genes, is also important in the initiation of cancer.

Hallmarks of Cancer

When talking about the challenges in treating cancer, it's helpful to talk about some of the hallmarks of cancer. Cancer cells are not just clones of cells that divide out of control, but have many attributes that help a tumor evade the body's immune system and treatments. Some of these include:

  • Sustained growth: The cell has to continue to grow and divide when normal cells would stop. In order to do this, the cell not only needs to grow, but also has to evade growth suppressors.
  • Resisting cell death: Normal cells die after a period of time (apoptosis). Cancer cells not only continue growing, but fail to die when they should.
  • Inducing angiogenesis: Cancers recruit normal cells nearby (tumor microenvironment) to form blood vessels to supply a tumor.
  • Invasion and metastasis: This can occur locally and to distant regions.
  • Avoiding destruction by the immune system: Our bodies know how to fight cancer cells, but these cells have found ways to "hide" from or deactivate the immune cells that would eliminate them.
  • Dormancy: In some cases, the ability to lie dormant for extended periods of time.

Risk Factors

There are a number of risk factors for cancer. These risk factors do not necessarily cause cancer, but are associated with an increased risk. Fortunately, several of these are avoidable, at least to some degree. In fact, some cancers may even be preventable with vaccinations.

That said, it's important to note that people can and do develop cancer even if they don't have any obvious risk factors. For example, lung cancer occurs in people who have never smoked, and lung cancer in never smokers is actually increasing. Risk factors for cancer include:


For many types of cancer, the risk increases with age. This makes sense when considering the causes above and the accumulation of mutations.

Environmental Exposures

A number of environmental exposures have been linked to cancer. Some examples include:

  • Radon gas: Exposure to radon gas in our homes is thought to be the second leading cause of lung cancer.
  • Ultraviolet light
  • Occupational exposures ranging from asbestos, to vinyl chloride, to wood dust have been associated with cancer.

Lifestyle practices: Some of the more modifiable causes of cancer are related to lifestyle practices. Some of these include:

  • Tobacco
  • Obesity: An elevated body mass index is a very important risk factor, and thought to be closing in on tobacco as the leading preventable cause
  • Diet: While studies looking at specific dietary nutrients have been mixed, a diet high in vegetables and fruits and low in processed and red meats has been linked to a lower risk of many cancers.

Infectious Diseases

Many people are surprised to hear that roughly 10% of cancers in the United States (and perhaps 25% worldwide) are associated with infectious diseases.

Microorganisms may cause cancer in a number of ways, ranging from direct damage to DNA, to creating chronic inflammation that leads to increased cell turnover (and a greater likelihood of accidents in cell division).

Examples include:

  • Viruses: There are many viruses associated with cancer. Some of these include hepatitis C, hepatitis B, Epstein Barr virus, HIV, and human papillomavirus (HPV) that is associated with not only cervical cancer, but also head and neck cancers, anal cancer, and more,
  • Bacteria: The bacterium Helicobacter pylori is linked to the development of stomach cancer.
  • Parasites: The parasite that causes schistosomiasis is associated with bladder cancer.

Immunization against hepatitis B and HPV is now available.


Genetics are important in many cancer types. In some cases, specific gene mutations lend a genetic predisposition to cancer. Genome-wide association studies are finding further evidence that the environment may interact with our genes to affect our risk of developing the disease.

Medical Conditions

Many medical conditions are associated with an elevated risk of cancer, ranging from rheumatoid arthritis to inflammatory bowel disease.

Medical Treatments and Medications

While radiation therapy and chemotherapy are used to treat cancer, they are also carcinogens themselves and may raise the risk of cancers in the future. A number of medications, especially immunosuppressive medications, have been associated with a higher risk of cancer.

Diagnosis, Staging, and Screening

The diagnosis of cancer begins with a careful history and physical, including a family history of cancer.

Blood Tests

Depending on the type of cancer, blood tests may raise suspicion. For example, a very high white blood cell count may raise suspicion about possible leukemia. There are also a number of tumor markers that may be increased with different cancers.


Imaging tests are frequently used in the diagnosis of cancer. This includes tests such as:

  • Ultrasound
  • Computed tomography (CT scan)
  • Magnetic resonance imaging (MRI)
  • Positron emission tomography (PET scan)
  • Bone scans
  • Thyroid scans
  • Scintigraphy


Procedures are also frequently used when diagnosing cancer. Some methods include:

  • Biopsies, including taking a sample of tissues, as well as liquid biopsy looking for tumor DNA in a blood sample
  • Endoscopic studies, such as colonoscopy, bronchoscopy (lungs), or cystoscopy (bladder)
  • Bone marrow aspiration/biopsy

Specialized Testing

Special tests are often used to further characterize tumors, such histochemistry, genetic sequencing, and more.


Once a cancer is diagnosed, in many cases staging is done. Staging is a critical step with many tumors in order to define the best treatment options.


We currently have cancer screening tests for a number of different cancers. Some of these include:

Genetic screening may also be done to look for a hereditary predisposition to cancer.


The treatment of cancer has advanced tremendously over the last century, with new modalities being added frequently. One of the most important factors when talking about treatment is to look at the goal of treatment.

In some cases, treatments are used in attempt to cure a cancer. In other cases, it's hoped that treatment will extend life. Sometimes, treatments may have little chance for inducing a cure or even extending life, but can greatly improve a person's quality of life while living with cancer.

There are two primary categories of treatment:

  • Local treatments are those that treat cancer in the area where it originated, and include surgery, radiation therapy, and ablation techniques.
  • Systemic treatments are those that address cancer cells wherever they may be in the body, and include chemotherapy, hormonal therapy, targeted therapies, and immunotherapy.


Surgery often promises the best chance of a cure, though is not always possible. It is the mainstay of treatments for tumors such as breast cancer.

Radiation Therapy and Proton Beam Therapy

Radiation therapy and proton beam therapy can be used in a number of different ways. Most often, they are used before surgery (to decrease the size of a tumor) or after surgery (to reduce the chance of recurrence). Radiation therapy may also be used for palliative reasons, for example, to treat bone pain due to bone metastases.

A specialized type of radiation therapy, stereotactic body radiotherapy (SBRT) or cyberknife is sometimes used as an alternative to surgery. This therapy used high doses of radiation concentrated in a small area of tissue. It is also being used more frequently to treat areas of metastases from a number of tumors.


Chemotherapy uses cytotoxic drugs that kill cells that are rapidly dividing. Since it kills any cells that are dividing rapidly (such as hair follicles), side effects are common.

Hormone Therapy

Hormonal therapy is used commonly for cancers in which hormones work as growth factors to stimulate growth of the tumor, such as breast cancer or prostate cancer.

Targeted Therapy

Targeted therapies are treatments that target specific pathways in the growth of a cancer. The growth of precision medicine has come with learning about these pathways and finding ways to intervene.

The completion of the human genome project and the ability to perform genomic testing has resulted in significant improvements in survival for many cancers. Unfortunately, cancers often become resistant to these treatments in time.


There are many types of immunotherapy ranging from immune checkpoint inhibitors to cancer vaccines, to monoclonal antibodies, to CAR T-cell therapy and more. These treatments use the immune system or principles of the immune system to treat cancer, and have been a game-changer with at least some advanced cancers such as lung cancer and melanoma.

Other Treatments

From bone marrow and stem cell transplants to tumor treating fields, options for addressing cancer continue to expand.

Supportive Care

Supportive treatments are also extremely important in treating cancer. These treatments may include bone modifying drugs to treat bone metastases, stents, to bypass blockages in the esophagus, bronchi, or ureters, leukapheresis, to reduce a very high white blood cell count, and more.

A Word From Verywell

Despite advances in the diagnosis and treatment of cancer, there are many challenges that remain. Fortunately, a few advances not related to treatment are making life better for those who have had to face a diagnosis.

One of these is the growth of psycho-oncology and recognizing that addressing the emotional and spiritual health of people with cancer is as important as treating physical health.

The other major area is that of survivorship. Unlike conditions such as a heart attack where rehabilitation is the standard of care after treatment, there has been little follow-up for cancer survivors; many who are left with long term side effects.

This is changing, and oncology now promises to not only reduce the death rate but also to help people cope with the emotional impact of the diagnosis and move on after treatment with a healthier new normal.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."