What Screening Tests Check for Cancer?

The effect of cancer on society is enormous—over 1.9 million individuals are diagnosed with cancer every year in the United States. Half of men and one-third of women have a lifetime cancer risk. There are more than 200 types of cancers that can affect almost any area of the body. Such diversity makes it impossible to detect the disease with a single test. Therefore, diagnosis and staging can only be confirmed through complex testing procedures that depend on suspected cancer type.

The process of diagnosing cancers, from detecting them to choosing the right treatment strategies, can vary a bit. This is because each type of cancer usually demonstrates specific characteristics that doctors try to identify in the beginning. For example, if a patient is suspected of having breast cancer, the doctor will probably first perform an imaging test such as mammography or a magnetic resonance imaging (MRI) scan to confirm. However, if a patient is thought to have prostate cancer, oncologists will usually prescribe a blood test to measure the amount of prostate-specific antigen (PSA).

Although the diagnosis of cancer appears to be a complex process, the main tests that help identify and assess cancer progression can be divided into several main groups.

Physical tests

By using this kind of test, the doctor palpates areas of the body to look for lumps that may indicate cancer. During this examination, the doctor looks for abnormalities such as skin color changes or enlarged organs, which may indicate the presence of cancer. Physical tests are primarily used to detect various solid tumors (breast, prostate cancers, etc.) as well as cancers that are visually noticeable (carcinomas, melanomas, etc.).

Laboratory tests

Laboratory tests measure the levels of chemical components in body fluids and tissues. These tests help doctors identify abnormalities, which can be an indication of cancer.

The most common specimens measured through laboratory testing are blood and urine. Thanks to modern technology, even the slightest change in normal chemical composition (changes in the amount of glucose, electrolytes, enzymes, hormones, lipids, proteins, cell numbers, and other metabolic substances) can be detected.

Some laboratory tests used for cancer detection are a complete blood count and tumor markers tests. A complete blood count is usually performed in people with suspected leukemia. The test may reveal an unusual number or type of white blood cells, which confirms the diagnosis. Tumor marker tests are performed when a patient is suspected of having a cancer that releases specific substances (called tumor markers). These substances can then be detected in the patient's blood, urine, and tissue.

Detected deviations in laboratory testing does not always indicate cancer, as they may point toward other health problems. Thus, other tests should be used to officially confirm the diagnosis.

Imaging tests

Imaging is the process of producing pictures of body structures and organs, which lets doctors assess internal organs in a noninvasive way. It is used to detect tumors and other abnormalities, determine how the disease has spread, and evaluate the effectiveness of treatment provided. There are three main types of imaging used for diagnosing cancer: transmission imaging, reflection imaging, and emission imaging.

  • Transmission imaging: Transmission imaging uses electromagnetic waves that pass through the body structure. The waves pass very quickly through less dense tissues such as blood and fat, which then appear as darkened areas in the image. Stiff tissues such as muscles, tendons, and cartilage appear gray while bones and other dense structures appear white. Structure stiffness determines color difference and lets doctors interpret observed images. For example, if bone cancer is suspected, the affected area in the image would be darker instead of white. Transmission imaging examples include radiological examinations such as x-rays, computed tomography scans (CT scans), and fluoroscopy.
  • Reflection imaging: In reflection imaging, images are produced by sending high-frequency sound waves to certain body parts. These waves reflect off tissues and organs at varying speeds depending on the density of the structure. The “bounced” waves are then sent to a computer that analyzes them and produces black-and-white images. White or gray and black parts are observed due to the intensity of sound wave reflection. Dense organism structures like bone are very reflective and show as bright white. In contrast, soft tissues appear dark gray in the images. The best example of reflection imaging used in cancer detection is ultrasound.
  • Emission imaging: Unlike transmission and reflection imaging where tested body areas pictures are observed due to shadows cast by the body, in emission imaging the detected information is small radioactive molecules distribution or cells emitted radio frequencies excited by a strong magnetic field. That’s why this imaging technique is more sensitive than others and can help determine abnormal activity and tiny changes of tissues and organs. Whether radioactive particles or radio waves emitted by cells are detected, three main emission imaging technologies can be distinguished - photon-emission tomography (PET), single-photon emission tomography (SPECT)) and magnetic resonance imaging (MRI).

Endoscopy

Endoscopy is a medical procedure where a flexible plastic tube with a tiny camera is inserted into body cavities and organs, which allows doctors to look directly at the suspicious area. There are many types of scopes and each is designed to view particular areas of the body. For example, a colonoscope is used to detect growths inside the colon while a laparoscope is used to observe the abdominal cavity. If cancer is suspected after an endoscopy, additional tests are usually performed to confirm the diagnosis.

Biopsy

During a biopsy, a small tissue or fluid sample is surgically removed and examined under a microscope for the presence of cancer cells. All healthy cells look uniform under the microscope and appear orderly, organized, and similar in size and morphology. On the other hand, cancer cells vary in size and shape while lacking any apparent organization.

Biopsies are usually performed under local anesthesia and do not require an overnight hospital stay. If the tumor is filled with fluid, doctors will insert a long, hollow needle directly into the suspicious area to draw fluid for examination. Doctors usually also use ultrasonography or a CT scan to guide the needle to the right location. In most situations, a biopsy is the only way to definitively diagnose cancer.

Although there are different methods used to diagnose cancer, researchers still work extensively to improve existing ones and develop new diagnostic tools. It is the hope that the diagnosis and treatment of cancer will become even more effective in the future and that the term cancer will no longer sound like a death sentence.

References

R.L. Siegel, K.D. Miller, H.E. Fuchs, A. Jemal, Cancer statistics, 2022, CA. Cancer J. Clin. 72 (2022) 7–33. https://doi.org/10.3322/CAAC.21708.

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