Houston, Apr 2 (PTI) A first-of-its-kind drug targeting a fused gene found in many types of cancer has been found to be effective in 93 per cent of paediatric patients tested, scientists say.

Most cancer drugs are targeted to specific organs or locations in the body.

Larotrectinib is the first cancer drug to receive US Food and Drug Administration (FDA) breakthrough therapy designation for patients with a specific fusion of two genes in the cancer cell, no matter what cancer type.

“In some cancers, a part of the TRK gene has become attached to another gene, which is called a fusion,” said Ted Laetsch, an assistant professor at The University of Texas Southwestern Medical Center in the US.

“When this occurs, it leads to the TRK gene being turned on when it’s not supposed to be and that causes the cells to grow uncontrollably.

“What is unique about the drug is it is very selective; it only blocks TRK receptors,” said Laetsch, lead author of the research appearing in The Lancet Oncology journal.

Larotrectinib, targets TRK fusions, which can occur in many types of cancer.

While the TRK fusions occur in only a small percentage of common adult cancers, they occur frequently in some rare paediatric cancers, such as infantile fibrosarcoma, cellular congenital mesoblastic nephroma, and papillary thyroid cancer.

“Every patient with a TRK fusion-positive solid tumour treated on this study had their tumour shrink. The nearly universal response rate seen with larotrectinib is unprecedented,” Laetsch said.

The results of the larotrectinib trial in adult patients – a 75 per cent response rate – were published last month in the New England Journal of Medicine.

The TRK-fusion mutation can be present in many types of cancers, including lung, colon, thyroid, and breast cancer, as well as certain paediatric tumours.

TRK, short for tropomyosin receptor kinase, is a gene that plays a key role in brain and nervous system development and has a limited role in nervous system functions such as regulating pain in later life.

Larotrectinib belongs to a class of molecules known as kinase inhibitors, which work by cutting back on the enzymatic activity of a key cellular reaction, researchers said.

The selectivity of the drug means it does not cause the severe side effects associated with many traditional cancer treatments, and none of the patients with TRK fusions had to quit the study because of a drug-induced side effect, they said.

This is published unedited from the PTI feed.