What is a Symptom?

What is a Symptom?

A symptom is a very broad term that can used to describe any feeling or experience that is interpreted as abnormal. In medical terms, a symptom is something that a person complains of. This is in contrast to a sign, which is something that can be observed. A symptom can also be a sign – such as an uncontrollable shaking of the hands. Uncontrollable shaking or tremor can cause discomfort and may be the main complaint of a person but the shaking could also be observed thus being a sign. A person with a headache may complain of this symptom but it is not possible to observe the headache thus in this situation it would not be a sign.

Some type of unpleasant sign or symptom is often the first clue to suggest the presence of cancer. The problem with this is that many signs and symptoms are very non-specific and can occur without cancer. The key to distinguishing this is to understand what symptoms require further investigation. The presence of certain symptoms is often very anxiety provoking and may lead someone to assume that they have cancer when in fact the chances of them having it are rare.

In order to discuss symptoms fully it is important to be aware of some basic terms used to describe different types of symptoms.

Key terms to help understand discussions of cancer symptoms:

  • Sensitivity
  • Specificity
  • Positive Predictive Value
  • Negative Predictive Value
  • Symptom
  • Sign
  • Acute
  • Chronic
  • Intermittent
  • Positive test result
  • Negative test result

For example, pain in the breast is often interpreted as a sign of breast cancer and can be frightening. Even before the woman seeks evaluation from a doctor, she may become depressed or convinced that she has cancer. The facts are that breast cancer only very rarely causes breast pain and the vast majority of breast cancers are painless. Alternatively, instead of reading too much into a common symptom an important red flag can be overlooked and dismissed. For example, it is a common occurrence for an older man who has some blood passage with a bowel movement to attribute this to “hemorrhoids”. This may be a sign of colon cancer and to dismiss it as simply “hemorrhoids” may miss the early window of opportunity for an effective treatment or even cure.

The other way to consider symptoms is by their duration. Symptoms may be acute, chronic, or intermittent. Acute means occurring suddenly, chronic refers to a symptom that has been going on for some time and intermittent means it comes and goes. These terms are somewhat imprecise because a chronic diarrhea may be one occurring for 3 weeks or 3 years.

Another way to think about symptoms is in terms of how likely they are to be a true sign of a cancer. This relates to statistical terms such as sensitivity and specificity. A very sensitive symptom or sign is something that is almost always seen with a specific disease. For example, finding some evidence of blood in the stool is almost always seen with colon cancer. Headache is almost always seen with a brain tumor. Both of these are very sensitive signs. However, we all know that every headache does not mean a brain tumor and every drop of blood in a bowel movement does not indicate a colon tumor. This brings us to the next concept of specificity. Both headache and blood found in the stool are not very specific. Specificity refers to the probability that a symptom will not be present in those without the disease. For example, there are many things that can cause blood in the stool (e.g. ulcers, hemorrhoids, diverticula, as well as tumors) however someone with no blood in the stool at all has a very low likelihood of having colon cancer. Thus we could say that blood in the stool has a low specificity but high sensitivity for colon cancer.

In addition to different ways to describe symptoms, they can also be classified based upon the type or stages of disease they are associated with. For example, one could consider symptoms of breast cancer that are associated with:

  • Symptoms of the breast that are probably not cancer (e.g. breast pain)
  • early symptoms of breast cancer (before diagnosis)
  • late symptoms of breast cancer (implying that the cancer has grown quite large)
  • symptoms of breast cancer spreading outside of the breast (i.e. metastases)

Another example of the opposite situation may be to consider a symptom or test that has a high sensitivity but low specificity. For example, many types of cancer can contribute to the formation of blood clots in veins which if untreated can be a deadly. A simple blood test can check for the possibility of blood clots called a d-dimer test. If the d-dimer test is negative (or says there is no possibility of a blood clot) then the likelihood of a clot being present is very, very low. If the d-dimer test is positive (meaning there is a possibility of a blood clot) this means that there may be a blood clot present but does not prove its presence and many other potential causes exist for a positive d-dimer. Thus, a d-dimer test is very sensitivity but has a low specificity for blood clots.

A symptom sometimes is investigated with a test. It is important to understand what a “positive test” or “negative test” means. If blood work is done to investigate for a possible heart attack and the blood work shows evidence of a heart attack, this would be a positive test. It is not uncommon for someone to think, “my test was positive, so that means the outcome was good.” In fact the opposite is true. If a genetic test done to look for a cancer gene such as BRCA-1 is reported as a negative test, this means you do NOT have the cancer gene and this is good news NOT negative news.


  1.  www.womenshealth.gov/breast-cancer/breast-cancer-symptoms/
  2. www.cdc.gov/cancer/lung/basic_info/symptoms.htm
  3. Diagnosing cancer in the symptomatic patient. Salzman BE, Lamb K, Olszewski RF, Tully A, Studdiford J. Prim Care. 2009 Dec;36(4):651-70; table of contents. Review.PMID: 19913180.
  4. Goldman, L ; Schafer A.I. (2011). Goldman: Goldman’s Cecil Medicine, 24th ed. Chapter 182. New York, NY: Elsevier Saunders.
  5. This article was originally published on September 3, 2012 and last revision and update was 9/4/2015.