Cancer is often discovered when people go to their doctor because they have discovered a lump or spot or they have symptoms that the doctor decides need to be investigated further. There is no single test that will diagnose cancer. Instead, a range of tests will be used, starting with a physical examination. After that, the doctor might decide that blood tests are needed where the blood is examined for the biochemical signs of cancer or the presence of cancerous cells. Different medical imaging techniques will also be used such as X-rays, CT scans, MRI, ultrasound, PET scans and endoscopic examinations.
Screening to identify cancer early
Because it is important to identify cancers as early as possible, screening is used with certain cancers. Cancer screening involves regularly testing people who don’t otherwise have any symptoms.
New Zealand has two organised screening programmes – screening for cervical cancer, and mammography breast screening, where women in the 45–70 age group are encouraged to have a mammogram every two years. Breast screening in this age group has been shown to significantly decrease the death rate from breast cancer. A mammogram can find lumps that are too small to be found by breast self examination, which means that, if it is cancer, it is more likely to be treated before it has spread to other tissues.
Some forms of cancer don’t have an organised screening programme but there are tests available to check for them. For example, there are different imaging technologies that can be used to screen for melanoma. In mole mapping, photographs are taken of the whole body, locating all the different moles on the body. In addition, any mole that looks suspicious is investigated further using a microscope called a dermascope that looks at the surface of the skin. Both types of images are digitally recorded and archived and can be used to track any changes in the skin. Another technique is siascopy, which checks how far melanocytes have travelled into the skin. If they go further than they should, it may indicate that a mole may actually be a melanoma.
There are two screening tests for prostate cancer in men. A doctor can feel the back of the prostate gland (a site where most prostrate cancers form) by probing the rectum. Blood can also be tested for a component called prostrate specific antigen (PSA). Abnormally high levels may indicate prostrate cancer.
A positive result in any screening does not necessarily mean that the person has cancer but it does mean that further investigation is needed. For example, if breast or prostrate cancer is suspected, the next step might be to ultrasound the breast or scrotum to get a better picture of what is actually there.
If a lump or suspicious spot is found, a biopsy (where a sample of the tissue is examined in a laboratory) is needed to confirm whether it is cancer or a more benign growth, and if it is cancer, what type of cancer it is.
The sample can be taken during an endoscopic examination, or a fine needle can be inserted into the lump and a sample of cells drawn out (fine needle biopsy). For lumps that are deep within the body, ultrasound or CT scanning can be used to guide the needle. A thicker needle is used in a core biopsy so that more tissue can be sampled, or part or the whole of the lump can be removed by surgery. In the case of a suspected melanoma, the whole mole would be removed.
In the laboratory, the sample is examined by a pathologist – a medical doctor who has specialised in diagnosing diseases by looking at the tissues or fluids of the body. A chemical pathologist looks at the chemical composition of blood, while an anatomical pathologist looks at tissues and cells underneath a microscope to see if they are different.
The pathologist looks for cells with an enlarged nucleus that are multiplying rapidly in a disorganised way and are more densely packed than normal cells.