One of the most exciting areas of cancer research is the development of tests that can detect different cancers at the earliest stages. These tests, often called multi-cancer early detection (MCED) tests, search for bits of DNA or RNA that are shed by tumor cells into the bloodstream. Then, they use artificial intelligence (AI) to help us pinpoint where the cancer most likely originated. This is certainly exciting, as a positive test would enable doctors to look for early-stage cancers when they are most curable.
MCED tests are a type of test known as a “liquid biopsy.” Liquid biopsies use a sample of blood to identify specific biologic signals in DNA, RNA, or proteins released by cancer cells into the blood. They are currently used in some people known to have cancer and can help doctors recommend the best treatment plan. However, MCEDs are different from these approved liquid biopsies because they are used in people with no symptoms or signs of cancer, instead of people known to have cancer, and they assess multiple biomarkers to determine if there is a strong likelihood someone has cancer and, if so, where it could be located. This is certainly exciting, but we still need to accurately understand the performance of these tests in larger groups of people.
There are many MCED tests in development that are intended to screen healthy people for multiple types of cancer with a single blood draw. As part of the Cancer Moonshot initiative to halve cancer deaths in the United States within 25 years, President Biden is supporting research that will study the efficacy of multiple types of early screening tests in up to 250,000 people ages 45 to 70. It is hoped that these tests would become part of routine medical care, much like drawing a cholesterol panel with a primary care doctor.
The harms from using MCED tests to screen for cancer are unknown. What’s the best test? What happens if, following a positive MCED test, you can’t find a cancer? How many people will end up undergoing unnecessary invasive tests to find a cancer? Will people stop the screening that we know is beneficial, such as colonoscopies and mammograms, before we have enough information about how to integrate MCED tests into routine care? Will a blood test make screening more accessible, or will it worsen disparities in care? Will these tests lead to overdiagnosis of indolent, or slow-growing, cancers? And most importantly, will these tests reduce how many people die from cancer?
MCEDs have the potential to mark a significant breakthrough in the race to cure cancer by dramatically enhancing patients’ lives through earlier cancer detection. But it’s clear that even if we improve the technology around these tests, there is much that remains unknown and needs to be studied.
While we start to better understand the science and application of this new technology, it is important for patients to keep up with the cancer screening that we already consider effective and recommended. This includes breast cancer screening with mammography, cervical cancer screening with human papillomavirus (HPV) tests and Pap tests, and colorectal cancer screening with colonoscopies and stool tests.
Getting people back to regular, recommended screening is especially important after the COVID-19 pandemic caused so many disruptions in our health care system. In fact, it is estimated that COVID-19 caused more than 9 million missed cancer screenings in 2020, according to a study in JAMA Oncology. And, although we are making up lost ground, there are many people who have not had the opportunity to have these screening tests.
It’s my hope that one day, we will be able to use MCED tests to cure more cancer and dramatically reduce the toll of cancer worldwide.