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About Cancer Screening | About Multi-Cancer Detection (MCD) Tests
Cancer screening tests are used to check for cancer or signs of cancer risk before a person has symptoms. There are two kinds of benefits from cancer screening tests: detection of abnormal cells that can be removed or treated before they become cancer (precancers), and detection of cancer at an earlier stage when it may be more treatable, leading to improved survival.
Cancer screening is not a stand-alone test. The success of a cancer screening test depends on more than just how well the test works. It also depends on the accuracy and affordability of the test, on the diagnostic workup needed after initial testing, and on effective cancer care delivery.
Tests to detect cancer or cancer risk come in many forms:
- Physical exams to check general signs of health. These exams can uncover visible signs of disease, such as lumps, abnormal moles, or enlarged organs.
- Imaging procedures, which take pictures of areas inside the body.
- A mammogram is a screening test for breast cancer. This test is an x-ray picture of the breast. Mammography has been shown to decrease the risk of dying from breast cancer by detecting it earlier when it is usually easier to treat.
- Low-dose computed tomography (CT) is used to screen for lung cancer. It has been shown to decrease the risk of dying from lung cancer in heavy smokers. The procedure makes a series of detailed pictures of the lungs using a type of x-ray machine.
- Direct observation tests, which involve visual examination of tissue for abnormal growths. A colonoscopy is a screening test for colorectal cancer. In this test, the rectum and colon are examined using a flexible lighted tube with a lens for viewing.
- Laboratory tests, which analyze samples of tissue, blood, urine, or other substances in the body. For example, health care professionals take a sample of cervical cells to screen for cervical cancer with a Pap test and to check for infection with human papillomavirus.
Additionally, standard screening methods for colon and cervical cancers can detect precancers that can be removed (for example, polyps), and thus prevent the development of a cancer in addition to detecting cancer early when it may be easier to treat successfully.
Cancer screening tests are used to check for cancer or signs of cancer risk before a person has symptoms. Cancer screening is not a stand-alone test. For example, after a positive cancer screening test, more tests are needed to make a diagnosis of cancer.
No. A screening test alone cannot diagnose cancer. A cancer screening test identifies something abnormal, and then more tests must be done to determine whether a person has cancer and what type. These are called diagnostic tests.
No. A screening test can miss the presence of cancer, leading to a false-negative test result. For example, mammograms may appear normal even though breast cancer is present. Overall, screening mammograms miss about 20% of breast cancers that are present at the time of screening.
MCD tests, also referred to as MCD assays or liquid biopsy tests, measure biological substances that cancer cells may shed in blood and other body fluids — such as circulating tumor cells, tumor DNA and other analytes — that may suggest the presence of cancer.
MCD tests differ from other cancer screening tests in two main ways. First, they use a single blood test instead of x-rays or imaging tests (such as mammography) or other medical procedures (such as colonoscopy). Second, they check for many types of cancer from different organ sites at the same time — incuding some cancers that existing screening tests do not check for.
Using a sample of blood, urine, or other bodily fluids, these tests measure biological substances released by tumor cells that indicate the possibility of cancer. No MCD tests screen for every type of cancer and right now each test only includes some cancer types.
MCD tests are new. They are just beginning to be evaluated to see how well they function as cancer screening tools. It is important to study these tests in clinical trials to better understand important questions including who should get these tests, what should be done after receiving a positive or negative result and whether these tests can actually save lives.
While MCD tests analyze molecules released by tumor cells, genetic tests for cancer risk look for specific inherited patterns in a person’s genes, including healthy cells. Genetic variants can have harmful, beneficial, neutral (no effect), unknown, or uncertain effects on the risk of developing diseases. Harmful variants in certain genes are known to be associated with an increased risk of developing cancer. These inherited variants are thought to contribute to about 5% to 10% of all cancers.
Genetic tests are usually requested by a person’s genetic counselor, doctor, or other health care professional who has reviewed the individual’s personal and family history. The genetic test options from which a health professional may select include those that look at a single gene and those that look for harmful variants in multiple genes at the same time. Genetic testing is done on a small sample of bodily fluid or tissue—usually blood, but sometimes saliva, cells from inside the cheek, or skin cells. The sample is then sent to a laboratory that specializes in genetic testing. The laboratory returns the test results to the doctor or genetic counselor who requested the test.
Multiple MCD tests are in development, and some are entering the marketplace. To date, no MCD tests have been proven to save lives from cancer.
No. The FDA approves devices and tests differently from how it approves medicines. No MCD tests have been approved by the FDA. However, some companies are offering the tests to physicians and consumers as laboratory developed tests (LDTs). LDTs are tests that are designed, manufactured, and used within a single laboratory. Laboratories offering LDTs are required to show that they measure what they say they can measure. The federal regulation of LDTs does not require evidence that they provide a clinical benefit to patients, such as diagnosing cancer early.
A few MCD tests have received a Breakthrough Device Designation from the FDA, but this does not mean they have gone through the FDA’s rigorous premarket review process.
This is a rapidly evolving emerging technology. Because MCD tests are not FDA approved there is no comprehensive central listing of MCD tests available to the public.
As a new tool for cancer screening, MCD tests make a prediction about the presence of cancer, not a diagnosis. Some MCD tests suggest the most likely organ site of the potential cancer. Additional testing will be required to provide a diagnosis.
It depends on which MCD test you take, as each MCD test typically targets a different group of cancers. For example, one test may look for colorectal, bladder, and prostate cancer. And a different MCD test may detect lung, colorectal, and pancreatic cancer. As of now, there are no MCD tests that screen for every possible type of cancer.
The National Cancer Institute’s (NCI) Cancer Screening Research Network (CSRN) is studying emerging screening technologies, such as MCD tests, to determine if these technologies can help save lives.