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Cancer Treatment Principles


Robert Peter Gale

, MD, PhD, DSC(hc), Imperial College London

Reviewed/Revised Sep 2022

Treating cancer is one of the most complex aspects of medical care. It involves a team that encompasses many types of doctors working together (for example, primary care doctors, gynecologists or other specialists, medical oncologists, radiation oncologists, surgeons, and pathologists) and many other types of health care practitioners (for example, nurses, radiation therapists, physiotherapists, social workers, and pharmacists).

Treatment plans take into consideration the type of cancer, including its location, its stage Staging Cancer Cancer is suspected based on a person's symptoms, the results of a physical examination, and sometimes the results of screening tests. Occasionally, x-rays obtained for other reasons, such as... read more (how large and widespread the cancer is), and its genetic characteristics, as well as specific characteristics of the person being treated.

Treatment decisions also take into account other factors, including

  • The likelihood of cure or of prolonging life when cure is not possible

  • The effect of treatment on symptoms

  • The side effects of treatment

  • The person's wishes

People undergoing cancer treatment hope for the best outcome and the longest survival with the highest quality of life. However, people must understand the risks involved with treatment. They should discuss their wishes regarding medical care with all of their doctors and should participate in decisions about treatment (and create written advance directives Advance Directives Health care advance directives are legal documents that communicate a person’s wishes about health care decisions in the event the person becomes incapable of making health care decisions. There... read more ).

Even when a cure is impossible, symptoms resulting from the cancer can often be relieved with treatment that improves the quality of life (palliative therapy). For example, if a tumor cannot be removed surgically, radiation to the tumor may shrink it, temporarily reducing pain and symptoms in the immediate vicinity of the tumor (local symptoms).

Because treatments are complex, specific approaches to care, called treatment protocols, have been developed to ensure that people receive the safest and most effective care. Treatment protocols ensure that people receive a standard approach derived from careful scientific experiments. Protocols are typically developed and refined through clinical trials. A clinical trial allows doctors to compare new drugs and treatment combinations with standard treatments to determine whether new treatments are more effective. Often, people with cancer are offered the opportunity to participate in such a trial, but not all people with cancer are eligible for a clinical trial.

Response to cancer treatment

A complete response (remission) occurs when a cancer disappears for any length of time after treatment. Doctors regularly monitor people who are being treated or have been treated for cancer. This usually consists of imaging tests and or laboratory tests to monitor the cancer's response to treatment and to identify cancer quickly if it returns.

Some cancers produce proteins that are detectable in the bloodstream. These substances are called tumor markers. An example is prostate-specific antigen (PSA). PSA levels increase in men with prostate cancer Prostate Cancer Prostate cancer begins in the prostate gland, an organ found only in males. The risk of prostate cancer increases as men age. Symptoms, such as difficulty urinating, a need to urinate frequently... read more Prostate Cancer . Most tumor markers are not specific enough to be useful in screening (detecting a cancer before a person develops symptoms) or diagnosing cancer because a number of disorders other than cancer can cause these substances to appear in the blood. However, tumor markers (such as PSA and cancer antigen [CA] 125 for ovarian cancer) can help doctors assess a person's response to treatment. If the tumor marker was present before treatment but no longer appears in a blood sample after treatment, the treatment has probably been successful. If the tumor marker disappears after treatment but later reappears, the cancer has probably returned.

Cure is obviously the most successful outcome. A cure means that all evidence of cancer disappears and does not return over a long period of observation. With some forms of cancer, doctors consider people cured if they remain disease-free for 5 years or longer. With other forms, a longer period is required before the person is considered cured.

With a partial response, the size or extent of a cancer (for example, as seen on imaging studies such as x-rays, computed tomography [CT], and positron emission tomography [PET]) is reduced by more than half, although cancer remains visible on imaging studies. With a partial response, the person usually has fewer symptoms and may have a prolonged life, although the cancer grows back in most cases. The duration of response is measured from the time of the partial response to the time when the cancer begins to enlarge or spread again.

In some people, treatment does not lead to a complete or partial response, but the cancer may not grow or spread and the person may experience no new symptoms for an extended period of time. This response is also considered beneficial. In the least successful response, the tumor continues to increase in size or new sites of disease appear despite treatment.

Relapse occurs when a cancer that has completely disappeared returns later.

The disease-free interval is the interval between the time cancer completely disappears and when it returns.

Total survival time is the interval from diagnosis of cancer to the time of death.

Some types of cancer, such as breast cancers or lymphomas (tumors of the lymph nodes), are termed responsive because they tend to respond well to chemotherapy or radiation therapy. Other cancers, such as pancreas or brain cancers, are termed resistant because most do not respond to chemotherapy or radiation therapy. Some tumors, such as many in the digestive tract and lungs, often respond to chemotherapy at first but later become resistant. Metastatic cancers (cancers that have spread to other sites) are largely incurable.

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