By Ann Miller Baker
Imagine one drug that can target and kill malignant cells for some patients with many types of cancer. A new drug called Vitrakvi (larotrectinib), approved by the U.S. Food and Drug Administration today, shows promise of doing just that for both adults and children with a variety of sometimes rare cancers that share one specific genetic mutation.
The mutation, called a TRK fusion, occurs when one of three NTRK genes becomes mistakenly connected to an unrelated gene and ignites uncontrolled growth. By solely targeting this mutation, the drug is designed to turn off growth signaling with a minimum of other toxicities.
According to the drug manufacturer, Loxo Oncology, this specific mutation can occur in a small subset of various adult and pediatric solid tumors ranging from cancers of the appendix, bile ducts, breast, lung, pancreas and thyroid to melanoma, GIST and various sarcomas.
In certain rare tumor types, such as secretory breast, secretory salivary gland and infantile fibrosarcoma, TRK fusions are more common, affecting greater than 60 percent of both adult and pediatric patients with these forms of cancer.
While less than one percent of all cancers carry this mutation, that still represents potentially thousands of patients who now have a new option. “For patients with this specific mutation, Vitrakvi is a magic bullet that works almost every time,” said Dr. Damon Reed, associate member of Moffitt’s Sarcoma Program and leader of its Adolescent and Young Adult Program.
“Oncologists would typically consider a drug successful if it works in one out of three patients, or even one out of five,” added Dr. Reed. Vitrakvi worked in the majority of patients who participated in two previously published studies. “In the first, 75 percent of adult patients had their tumors shrink. For the pediatric trial, 90 percent of patients had their cancer shrink. We don’t see results like that very often.”
Reed characterized Vitrakvi as a “miracle drug” for patients whose cancers bear the mutation, “but the issue is finding the patients.” Unlike single-point mutations that can be detected by most genetic screening panels, the TRK fusion mutation requires next-generation sequencing panels that specifically include TRK genes, such as the STAR panel at Moffitt Cancer Center.