In November 2018, the FDA announced the accelerated approval of a new type of cancer drug, larotrectinib (Vitrakvi), the first to target a specific cancer gene rather than a cancer “type,” such as breast or colon cancer. This is a monumental shift in cancer treatment because this drug is “tissue agnostic”—it doesn’t care where the cancer is, but rather what drives its growth.
Vitrakvi targets the gene mutations known as neurotrophic tyrosine receptor kinase (NTRK) fusions. NTRK genes provide the fuel that helps some solid tumors grow, including infantile fibrosarcoma, soft tissue (muscle) sarcoma and tumors of the salivary gland, thyroid and lung. By targeting NTRK, this drug seeks to stop the growth of these tumors, which often have metastasized to numerous places, can’t be removed surgically or have not responded to other treatments. Unlike many cancer drugs that must be given intravenously,Vitrakvi is taken as a pill or oral solution.
Targeting specific genes is relatively new and reflects what scientists have learned about cancer mutations in the last decade…and even the last year. For example, pembrolizumab (Keytruda) was approved by the FDA in 2017 to treat melanoma, the deadliest form of skin cancer. Though it wasn’t designed to be tissue agnostic, it was found to be just that. Keytruda targets gene mutations called mismatch repair gene mutations. As these genes have been found in cancers in other locations, Keytruda has been given further approval to treat lung, head and neck and bladder cancers with that genetic profile.
FAST-TRACKING CANCER CARE
The accelerated approval of Vitrakvi was based on several early clinical trials with just 55 adults and children with various NTRK positive tumors. These tumors had a 75% response rate to the drug—a complete response for 22% of patients and a partial response for 53%. Before Vitrakvi, many of these cancers were simply untreatable.
In October 2018, an additional year of follow-up data was presented at the European Society for Medical Oncology meeting. More good news: The overall response rate of the original 55 patients had improved to 80%. There were also 67 new patients who had an overall response rate of 81%. It was also being used to treat NTRK positive tumors in more locations—the colon, gastrointestinal system, breast, bone, pancreas and skin (melanoma).
Patients on Vitrakvi continue to take the drug indefinitely or until it stops working or has to be stopped due to side effects. Common side effects include fatigue, nausea and vomiting, cough, constipation or diarrhea, and dizziness—neurological problems, mostly minor, occurred in about half of patients. But more serious liver damage may occur, so blood tests are needed to check liver function. Vitrakvi is approved to treat NTRK positive cancers in both adults and children, but it cannot be taken by women who are pregnant or breastfeeding.