(The following is an excerpt from an article published in Harvard Public Health; you can access the full article here.)
Article written by Madeline Drexler. Illustrations by Stephanie Dalton Cowan.
Prevention via Detection
With many tumors, there is a lag time of 20 years or more between the development of the first cancer cell and the onset of end-stage metastatic disease. Knowing each cancer’s basic biology could lead to a host of new technologies that register early biomarkers of the disease, potentially opening up new ways to head off malignancy before it spreads. That prospect would be transformative for the implacable cancers that don’t cause symptoms until they have reached their late and often incurable stages.
Among these promising biomarkers are proteins that signal early tumors, DNA or RNA, small molecules, circulating tumor cells, immune cells, and other infinitesimal biological entities. Scientists are also fashioning synthetically engineered biomarkers that harness the body’s own biology to spin off early signals of disease. “It’s a matter of screening technology getting refined enough so that you can find two suspicious molecules in four liters of blood which suggest you are at risk for or have already developed cancer,” says Rebbeck.
Sangeeta Bhatia, a biomedical researcher and early-detection pioneer, and the John J. and Dorothy Wilson Professor of Engineering at the Massachusetts Institute of Technology, injects nanoparticles into the bloodstream that respond to cancer-associated enzymes. When the particles find the enzyme for which they are designed, a chemical reaction produces “reporters”: synthetic chemicals eliminated in the urine that can tip off researchers to a nascent malignancy. Her lab is searching for highly specific biomarkers for often-elusive tumors of the ovary and lung and in colon metastasis. Clinical trials for the technology will begin later this year.
“Ultimately, we’d like to be in a place where you could do a urine test on a paper strip for a defined set of cancers,” Bhatia says. Other scientists envision, in the more distant future, continuous monitoring of cancer risk through smart toilets, wearables such as diagnostic imaging bras, and other passive and noninvasive technologies.
In clinical medicine, the value of screening tests is gauged by their sensitivity and specificity. Sensitivity measures a test’s ability to identify people who have the condition that is being tested for; a highly sensitive test will not generate false-negative results. Specificity measures a test’s ability to identify people who do not have the condition that is being tested for; a highly specific test will not generate false-positive results.
All the futuristic approaches described above require knowing that a technology’s molecular quarry is made by a certain kind of cancer cell and only that cancer cell—that is, the screening test must be highly specific. Since many tiny malignancies never go on to become metastatic disease—because the immune system reins in such cells—the ideal biomarker would not only tip off doctors to the presence of a cancer or precancer but also predict whether the suspect cells are aggressive or slow-growing. “One can imagine a day when healthy individuals are routinely tested for these biomarkers to detect early cancers, along with lipid concentrations to detect early cardiac disease, at periodic visits to their physicians,” the Harvard Chan School scientists wrote in Science in 2018.