The landscape of cancer treatment changed forever in 1998, when U.S. authorities approved the first genetically tailored precision cancer therapy. The drug, Herceptin, zeroes in on the activity of HER2—a gene that can make breast cancers especially aggressive compared with HER2-negative cancers. When the gene is mutated, it overproduces the corresponding human epidermal growth factor receptor 2 protein to trigger unhinged cell division. More traditional treatments attack both cancerous and healthy cells, but Herceptin goes after the root cause of a cancer’s growth by blocking the gene’s misbehaving proteins. Today, thanks to such targeted drugs, people with HER2-positive breast cancers have similar long-term survival odds as those who don’t.
The early success of this strategy ushered in precision oncology—treatment custom-designed to a tumor’s genetic signature. A new study in Cancer Discovery recently found that of the 198 new cancer drugs that the Food and Drug Administration has approved since Herceptin in 1998, 86 of them, or 43 percent, are classified as precision oncology drugs. “That fraction is a lot higher than what one would anticipate for precision oncology because it’s considered a relatively new field relative to standard therapies,” says study author Debyani Chakravarty, a molecular geneticist at the Memorial Sloan Kettering Cancer Center (MSK). But even though the growing number of available drugs would seem to make many more people eligible for treatment, a greater challenge remains: removing the practical access barriers that threaten precision oncology’s rise.
When a person is diagnosed with cancer, the standard of care has long been chemotherapy and radiotherapy. But these blunt instruments don’t distinguish normal cells from cancerous ones, so the resulting damage often causes harsh side effects, such as extreme fatigue, nausea and hair loss. Precision oncology specifies treatment based on the exact genetic mutations that drive the cancer in the first place. To determine eligibility for the treatment, people undergo biomarker testing—which usually involves the removal of some tumor tissue for genomic analysis. If this test detects certain biomarkers (molecular indicators of a cancer’s subtype), a person with cancer qualifies for precision therapy, either as a standalone treatment or in combination with other drugs. This method aims to minimize collateral damage by going after cancer cells with specific features. Biomarker testing also excludes people who are unlikely to benefit from the drug and who would only incur harmful side effects. Precision oncology’s central tenet is to administer the right drug at the right time to the right person.
“Not every cancer behaves the same way in every patient,” says Peter Nelson, a medical oncologist and vice president of precision oncology at the Fred Hutchinson Cancer Center, who didn’t participate in the new study. “The whole idea behind precision oncology is, ‘Can you define those differences?’”
The new study shows the precision approach is gaining traction. But has its growth benefited people with cancer overall? The study authors wondered how many new drugs appearing on the market represent a true innovation—the kind that broadens the range of cancers that doctors can confidently treat.
The authors sought an answer by sifting through MSK’s repository of tumor biopsy data. When the researchers noted which tumors bore biomarkers that could be targeted by FDA-approved precision drugs, they found that only 9 percent of the tumors could have been treated in 2017. By 2022 the number of people with cancer who were eligible increased nearly fourfold, to 32 percent. This shows that “patients are benefiting,” says study author and MSK senior scientist Sarah P. Suehnholz. “They do have the option to receive this expanded repertoire of drugs now.”
The study highlights the importance of sequencing tumors in the clinic to treat cancer, says Timothy Yap, a medical oncologist at the University of Texas MD Anderson Cancer Center, who wasn’t involved in the research. With more tumors becoming targetable, both Yap and Chakravarty say that all people with cancer should ideally undergo biomarker screening on the however-small chance that one or more drugs fit their disease profile.
Precision oncology may be opening new doors for cancer treatment, but the study authors acknowledge that their analysis doesn’t address whether people actually reap the benefits in the real world. “The question that remains,” Chakravarty says, “is what are the barriers to that patient receiving the drug?”
Access to treatment is often determined not by drug availability but by money. Though cancer drugs are usually covered by insurance, biomarker testing sometimes is not. People who can’t undergo such a test are ineligible to receive the precision drug.
This uneven distribution of benefits becomes more apparent across communities with inequitable access to health care. Certain locations may lack specialized cancer centers or expertise in interpreting biomarker test results. And not everyone has insurance coverage, a fact that walls off the latest available therapies from a significant number of people with cancer. Doctors in some countries don’t always recommend screening for certain biomarkers, because the chance that a person with cancer would qualify for a drug might be so tiny that it’s not considered worth the cost of the test.
Then “there’s still the larger piece of the pie,” Yap says, referring to the 68 percent of tumors that the study found were untreatable with FDA-approved precision therapy drugs as of 2022. To create new medications, drug developers often pile onto genetic targets that have already proved successful. Though this approach is important to weed out shifty cancers that have evolved their way past a drug, it doesn’t address mutations in other cases that have yet to be targeted at all.
The pharmaceutical industry has so far largely focused on oncogenes (genes that can turn a normal cell cancerous), but Yap says that more effort should go into targeting faulty tumor suppressor genes. Some cancers arise when these genes malfunction and can no longer keep cells from going rogue. Admittedly, mutated tumor suppressor genes are harder to develop drugs for, Yap notes—and they’re responsible for half of the cancers for which the pharmaceutical industry still has no treatment. “There’s a huge space that hasn’t been conquered yet,” he says.
Research is underway to find drugs for these elusive targets. One such effort is aimed at the tumor suppressor gene TP53, mutations of which appear in many cancers but have long been considered untreatable with medication; nearly three decades of research have yet to produce an approved drug. More than 30 clinical trials involving TP53 are currently underway, involving various drug strategies that range from culling mutated proteins to restoring healthy ones.
Experts say precision oncology will ultimately serve more people if drug developers expand the definition of “precision” to beyond DNA-level targets. Cancer can manifest from RNA and protein glitches, too, Yap says. These sources may lend themselves to other biomarker detection methods in addition to biopsy and genomic sequencing.
For example, Nelson describes the rise of molecular imaging techniques to suss out specific proteins that define prostate cancer subtypes. To get around prostate biopsy—an uncomfortable process that involves sticking a needle up and through the rectum—a clinician can instead administer radioactive tracers that selectively tag antigens on cancer cells so that under the glare of positron rays, the target-toting cancer cells will beacon their location.
With numerous drugs in development and with profiling methods on the rise, Nelson and Yap say it’s an exciting time for the field. “I do think it’s just the starting point of precision oncology,” Nelson says.
ABOUT THE AUTHOR(S)
Shi En Kim is a science writer based in Washington, D.C. Her work has appeared in Chemical & Engineering News, National Geographic, Hakai Magazine, Slate, Science News, and more. Follow her on Twitter @goes_by_kim
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