In recent years, researchers have been developing new drugs that may rapidly improve the ability to treat certain types of cancer. These medications are designed to target specific genetic traits of cancers, rather than specific types of tumors. By pinpointing genetic mutations, they can attack tumors regardless of where they grow in the body.
One such drug, called Vitrakvi (larotrectinib), was approved by the United States Food and Drug Administration (FDA) in 2018. It doesn’t target a particular cancer, such as breast or colon cancer. Instead, it treats tumors that carry a genetic feature, or biomarker, known as neurotrophic receptor tyrosine kinase (NTRK) gene fusion.
When they function normally, NTRK genes lead to the formation in the body of a type of protein called TRK proteins. But in abnormal cases, NTRK genes may become fused to other unrelated genes, which could trigger the growth of tumors. These mutations are uncommon, but they can occur in some rare cancers, including a very rare cancer affecting children called infantile fibrosarcoma. They may also appear in a very small percentage of common cancers, in solid tumors that arise in various parts of the body, including the lungs, thyroid gland and colon.
Vitrakvi, developed by Loxo Oncology, was approved under the FDA’s accelerated approval program, which enables the agency to “green light” drugs for serious conditions to fill an unmet medical need based on promising initial clinical trials.
The drug was studied in three trials, involving 55 children and adult patients diagnosed with solid tumors with NTRK gene fusion that had spread and did not respond to any other treatments. These patients’ tumors could also not be safely removed through surgery.
Overall, the drug had a 75 percent overall response rate. Of the 55 patients included in the trial, 53 percent had a partial response, in which they experienced either a reduction in the size of their tumors or tumors that stopped growing entirely. Meanwhile, 22 percent had a complete response, or their cancer was no longer detectable. Of these responses, 73 percent lasted for at least six months while 39 percent lasted for a year or more, the FDA reported.
Common side effects of the drug include fatigue, nausea, cough, constipation, diarrhea, dizziness, vomiting and liver damage. The drug should not be taken by pregnant or breastfeeding people because it could harm a developing fetus or newborn.
More clinical trials are needed to confirm Vitrakvi’s long-term safety and effectiveness. But Vitrakvi’s approval was important for a couple of reasons. For one, it was a significant step forward for precision medicine, which challenges a one-size-fits-all approach to cancer treatment. What’s more, it’s a single drug that could help treat many tumor types.
The population of people affected by NTRK fusion is small. But for these people, the benefits could be dramatic. Until Vitrakvi’s approval, there were no drugs for certain cancers that often carry this mutation. Vitrakvi is available as an oral capsule or a liquid formulation for both adults and children.
