A first-of-its-kind drug, termed larotrectinib, which targets TRK fusions has been demonstrated to be effective in 93% of pediatric patients tested. The drug is the first to be granted FDA breakthrough therapy designation for patients with a specific fusion of two genes in the cancer cell, no matter what cancer type.
TRK fusions occur in many types of cancer and whilst only small percentages occur in common adult cancers, this fusion occurs frequently in some rare pediatric cancers – such as infantile fibrosarcoma, cellular congenital mesoblastic nephroma and papillary thyroid cancer.
“Every patient with a TRK fusion-positive solid tumor treated on this study had their tumor shrink. The nearly universal response rate seen with larotrectinib is unprecedented”, explained lead author Ted Laetsch from the Harold C. Simmons Comprehensive Cancer Center (TX, USA).
Importantly, the selectivity of larotrectinib meant that it did not cause the severe side effects associated with many traditional cancer treatments and none of the patients with TRK fusions needed to quit the study because of a drug-induced side effect.
Additionally, the team demonstrated that the response was long-lasting for most patients. “For some of the targeted drugs in the past, many patients responded initially, but then resistance developed quickly. To date, the response to this drug seems to be durable in most patients,” explained Laetsch.
The next step in the research is a clinical trial involving a similar drug for those patients who developed resistance.