Cancer treatment has come a long way since Hippocrates proposed that it was caused by a buildup of black bile. Remedies ranged from powdered worms and ground elm poultices to, as recently as 150 years ago, bloodletting. With the advent of surgery, chemotherapy, and radiation, many cancers have evolved from almost certainly fatal to quite treatable and even curable.
But only in the last several decades have oncologists moved from a “one-size-fits-all” approach to being able to truly personalize patient care, using information about an individual’s tumor to tailor treatment. Just as we all have different fingerprints, personalities, and DNA, cancers possess distinctive features that reveal so much about how they operate. Called biomarkers—shorthand for biological markers—these are proteins, genes, or genetic mutations found in a person’s tumor, blood, or other body fluid that, thanks to pioneering research, clinical trials, and real-world practice, have revolutionized cancer treatment.
If one or more biomarkers are detected, it offers vital information as to what is driving the cancer, such as a specific mutation or cancer-fueling protein. That, in turn, reveals vulnerabilities in the cancer that medical oncologists can use to plan an attack using biomarker-based therapies like immunotherapy or targeted therapy. Five patients with, say, breast cancer, might each undergo different treatment protocols based on their cancer’s distinctive characteristics—and all of them could be successful.
For example, up to 20 percent of breast cancer patients have a mutation that results in excess amounts of a cancer-accelerating protein called HER2. If a person’s tumor is found to have this mutation, their cancer is considered HER2-positive. These tumors are highly susceptible to HER2 inhibitors (also called anti-HER2 therapies) such as trastuzumab (Herceptin) and pertuzumab (Perjeta) ,which, when infused or taken orally, hunt down and attack HER2-positive cancer cells with missile-like precision. (These are often used in combination with other treatments, like surgery, chemotherapy, or radiation.) HER2-negative patients, on the other hand, would not benefit from these medications. Depending on the presence or absence of other biomarkers, like ER (estrogen receptor) or PR (progesterone receptor), they would want to follow a different protocol. The use of medications that take specific aim at genetic abnormalities in a patient’s tumor is called targeted therapy.
Another class of biomarker-based treatment, immunotherapy, doesn’t directly pursue cancer cells, but rather harnesses the power of the immune system to wage an attack. Ordinarily, the immune system recognizes and disables foreign invaders, including viruses, bacteria, and precancerous cells, but certain biomarkers act like camouflage for cancer cells, allowing them to avoid destruction by hiding in plain sight. If a patient’s cancer shows elevated levels of one of these biomarkers, they would benefit from immunotherapeutic drugs that unmask the cancer cells, allowing the immune system to take action. Examples of immunotherapy include immune checkpoint inhibitors, monoclonal antibodies, T-cell transfer therapy, immune system modulators, and treatment vaccines.
By enabling doctors to predict which tumors are more susceptible to specific therapies, biomarkers lead to more successful outcomes while minimizing side effects. According to the American Cancer Society, the risk of dying from cancer dropped 32 percent between 1991 and 2019, meaning that about 3.5 million cancer deaths were prevented. Biomarker-based treatments are an important contributing factor. (Others include reduced rates of smoking, enhanced screening protocols, and the use of post-surgical chemotherapy for colon and breast cancer.)
In addition to finetuning treatment, biomarkers are used to determine where a tumor is located, how advanced it is, and whether or not it has spread to any lymph nodes; to help predict how aggressively a cancer will act; and to provide insight into how a cancer is responding once treatment is underway, as well as whether it might recur after treatment.
Biomarkers are also a critical component of certain cancer screenings, meaning they’re tested before any cancer symptoms have developed. Even if you’ve never had cancer yourself, you’re likely familiar with some of these. Prostate-specific antigen (PSA) and BRCA 1 and BRCA2, for instance, are biomarkers that, when detected, offer clues about a person’s future risk of developing prostate or breast cancer, respectively. (PSA and BRCA are also used when weighing treatment options after cancer has been diagnosed.)
Biomarker testing is typically one of the first steps to occur following a cancer diagnosis. It may even be performed on tissue sampled during a biopsy. It’s almost always covered by insurance. Some patients may be retested in the future, as biomarker levels can change with time.
