Cancer Doubts .com
  Information for patients researching their options

Learn about cancer and
Talk to your doctor with confidence

  Cancer information  

01 What is cancer?
02 Cancer symptoms and screening (how cancer is detected)
03 Causes of cancer
04 Can cancer be prevented?
05 Cancer Stages
(how long do patients live?)
06 Cancer treatment and therapy (how cancer is treated)
07 Types of doctors who treat cancer
08 Choosing a doctor (or getting a second opinion)
09 Preparing for Chemotherapy and Radiotherapy
10 Cancer support (patient psychology and feelings)
11 Cancer suport - How friends can help
12 Is it important to do my own research? (or do I just follow doctor's orders)
13 Cancer information (research your treatment options)
14 Alternative and complementary treatments for cancer
15 Avoiding dubious treatments
16 How medical research is done (how to read medical research papers)
A About this site

How is cancer detected? (screening)

In practice, cancer is often detected only when a patient feels physical discomfort, or demonstrates physical symptoms of being unwell (headaches, anemia etc). This is because cancers that are in that are in their early stages, for example when they are just a small number of cancer cells, often do not cause any symptoms to appear, so people are unaware that anything is wrong and doctors have no specific symptom to investigate.

It is often only when the cancer has become a large tumor mass that it causes physical symptoms to appear. For example in colon cancer, a tumor in the colon can grow until it penetrates the colon wall and causes it to bleed. This causes blood in the stool, which is often the first time a patient has any warning that something might be wrong and goes to see the doctor.

As a doctor examines the patient, he or she may have a hunch that a cancer is underlying cause and undertake a directed examination for a cancer. For example, in colon cancer, the doctor may perform a colonoscopy to visually inspect the colon for tumors. In other less accessible organs, such as the lungs, X-Rays, CT Scans or other scanning and imaging technologies may be used to look for signs of a tumor. The common imaging technologies today are:

  • X-rays - X ray radiation is sent through the body and collected on an imaging film. These X rays will pass through soft tissue. Only hard objects like bone or tumor masses will block X rays from passing through and appearing on the film. Tumors will appear as spots on an X-ray film.

  • CT scans - a computer controlled machine is used to send low doses of X ray radiation through the body. Unlike normal X-ray images which are only 2-dimensional (like a photo), the CT-scan machine performs thousands of imaging slices along the body. All the images are then assembled by the computer to create a 3-D view of the body. This can be effective in finding tumors.

  • PET Scan

    Image: PET scanner. Source: Wikimedia Commons.

  • PET scans - a glucose with dye is injected into the patient. Because cancer cells and tumors need to consume glucose to multiply, they will draw in the dyed glucose. The dyed glucose shows up duing a PET CT scan as bright spots. If a large bright spot is seen, then it is likely to be a mass of cancer cells (tumor). However, it should be noted that normal cells that are repairing body damage, such as healing after a surgery, also consume glucose and would also light up in the scan. As a result, this scan is only done when the patient has no obvious injuries or post-surgical healing.

  • MRI scans - a computer controlled machine sends a rotating magnetic field through the body, and the computer assembles the resulting images into an image of the body. MRI tends to be able to see into soft tissue better than X-rays (or CT scans). Because MRIs use a magnetic field, they are not suitable for anyone who has metallic implants in their body.
CT Scan Tumor

CT scan image showing a slice of the body. The radiographer has highlighted what he/she things is a suspicious mass in the body (in this case, a suspected tumor of the esophagus) Image source: Wikimedia Commons, used under the GNU license.

It is important to realize that there is no one best imaging technology. Certain tumors may appear on an MRI scan, but not on a CT scan, and so on. Doctors and radiologists are also needed to interpret the scanned images. For example, a tiny spot that appears on a scan of the lung may either be a tumor or a localized inflammation caused by air pollution. The doctor will need to make an assessment of what it could be. Often, supporting circumstances, such as a patient's history of inhaling smoke, or the results of biopsies and blood tests help the doctor make the determination.

Biopsies simply refer to the process of extracting some of the cells in the body (usually from a suspected tumor mass) and examining them under a microscope and/or with chemical tests. Depending on the location of the suspicious mass, the tissue sample can be taken using either a needle or through surgery. The tissue sample is then examined by a pathologist who can see if the cells are cancerous (Medical terminology: examining tissues samples under a microscope is called histology) .

Blood tests or urine tests can also help determine the presence of cancer. In many cases, cancer cells give off certain molecules (such as protein molecules) as they multiply, or cause normal cells in the body to give off certain molecules. These molecules are called markers, and we can test for their presence in the blood. Common markers include CA19-9, CEA, CA125.

Unfortunately, blood tests alone are usually not conclusive. This is because the markers that cancer cells give off can also be produced by normal healthy cells. For example, the CEA marker molecules are given off by cells that are multiplying, and this happens in pregnant women when fetuses are growing, or when the body is trying to heal itself from damage. Smokers for example, typically have higher CEA levels than non-smokers, because their lungs are constantly inflamed by smoking. Some cancer cells also do not give off markers, making a blood test alone inconclusive.

As a result, there is no easy way to screen for cancers among the general population. Blood tests are easy to perform, but their value is limited because they often present false negatives (a person may have a cancer, but it could be a variant that doesn't emit any markers until at a very late stage). The only way to thoroughly check for cancer is to undertake specific examinations: colonoscopies, PET scans etc. This is both very costly, and presents risks to people. For example, PET scans utilize radiation, and excessive amounts of radiation will end up harming. Likewise, colonoscopies present a small risk of danger because a colon could be accidentally punctured during the examination. These tests are also expensive and time consuming. Subjecting oneself to a battery of tests might end up causing more problems than would be solved.



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Medical information for cancer I am not a medical professional; please consult your doctor for a medical opinion. This is my attempt to explain cancer to anyone who is affected by it. If this site helps just one person, then it will have served its purpose.


 Cancer Links
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Complementary and Alternative Medicine Information
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Maitake Products [D-Fraction]
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Vita Green [Yun Zhi extract]
Clinical Trials
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Research Papers
National Center for Biotechnology Information
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New Drug Approvals / Drugs in the pipeline
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Helpful Books and Sites
Chemotherapy and radiation therapy survival guide
The biology of cancer
Patient Stories
Andrew Grove
Steve Dunn



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