A plain language summary looking at how well larotrectinib works and how safe it is for people with TRK fusion-positive thyroid cancer

What is this summary about? This is a summary of a publication on TRK fusion-positive thyroid cancer. TRK fusion-positive means that each participant’s cancer had a specific change in the tumor’s genes, called an NTRK gene fusion, that caused their cancer. The 2 main types of TRK fusion-positive thyroid cancers that the researchers looked at in this study were differentiated thyroid cancer (DTC) and anaplastic thyroid cancer (ATC). The researchers wanted to know whether the study drug, larotrectinib, could shrink the participants’ cancers and what medical issues happened during treatment that the researchers thought could be related to larotrectinib. What were the main results reported by the researchers? Researchers found that, among the participants with TRK fusion-positive DTC who took larotrectinib, 86% (18 out of 21) of the participants had their tumors respond to treatment. This means their tumors shrank by over 30% or disappeared completely. 100% of the participants whose tumors responded to treatment continued to respond for 12 months (1 year). Researchers also found that, among the participants with TRK fusion-positive ATC who took larotrectinib, 29% (2 out of 7) of the participants had their tumors respond to treatment. 1 of the 2 participants whose tumors responded to treatment continued to respond for 12 months (1 year). Among all of the participants who took larotrectinib, researchers found that 90% developed medical issues, also called adverse events, that the researchers thought might be possibly related to larotrectinib. This was 26 out of 29 participants. Most of these adverse events were classified as mild. What do the results mean? Larotrectinib could be a treatment option for people with TRK fusion-positive differentiated thyroid cancer (DTC). It is not as effective in people with anaplastic thyroid cancer (ATC) and is likely not an appropriate treatment for ATC. Further research is needed to understand why larotrectinib is not as effective in people with ATC. Who sponsored this study? This study focused on 3 trials that were sponsored by Bayer Healthcare and Loxo Oncology, Inc., a wholly owned subsidiary (part or sub-company) of Eli Lilly and Company.