"A firstofitskind drug targeting a fused gene found in many types of cancer was effective in  percent of pediatric patients tested researchers at UT Southwesterns Simmons Cancer Center announced.    Most cancer drugs are targeted to specific organs or locations in the body. Larotrectinib is the first cancer drug to receive FDA breakthrough therapy designation for patients with a specific fusion of two genes in the cancer cell no matter what cancer type. The research appears in The Lancet Oncology.    In some cancers a part of the TRK gene has become attached to another gene which is called a fusion. When this occurs it leads to the TRK gene being turned on when its not supposed to be and that causes the cells to grow uncontrollably. Whats unique about the drug is it is very selective it only blocks TRK receptors said lead author Dr. Ted Laetsch Assistant Professor of Pediatrics and with the Harold C. Simmons Comprehensive Cancer Center.    More information    Lancet Oncology paper    News release on NEJM paper    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 pediatric cancers such as infantile fibrosarcoma cellular congenital mesoblastic nephroma and papillary thyroid cancer said Dr. Laetsch who leads the Experimental Therapeutics Program ETP in the Pauline Allen Gill Center for Cancer and Blood Disorders at Childrens Health in Dallas.    Every patient with a TRK fusionpositive solid tumor treated on this study had their tumor shrink. The nearly universal response rate seen with larotrectinib is unprecedented Dr. Laetsch said.    Among them was yearold Briana Ayala of El Paso who aspires to a career in fashion design. In  Briana was found to have a rare tumor in her abdomen wrapped around her aorta the largest artery in the body.    Surgeons in her hometown said it would be too dangerous to operate so her family brought Briana to Childrens Health in Dallas where UT Southwestern Professor of Surgery Dr. Stephen Megison had to remove portions of her aorta while removing most of the tumor.    But the cancer started to grow again and no further treatments were available.    Dr. Laetsch sent her tumor for genetic testing and found that Brianas cancer had the TRK fusion meaning the new drug might help.    Briana enrolled in the phase  clinical trial of larotrectinib and began taking the drug twice a day. Within weeks her pain and the swelling in her abdomen diminished and scans showed her tumors had shrunk significantly.    Nearly two years later Briana is back in school and playing with her dog Goofy and the familys seven parakeets. Shes also been able to pick up her sketch pad and her dreams of a New York City fashion career.    These are the kind of amazing responses weve seen with larotrectinib said Dr. Laetsch and this is why Im so excited about it.    The results of the larotrectinib trial in adult patients  a  percent response rate  were published last month in the New England Journal of Medicine.    The TRKfusion mutation can be present in many types of cancers including lung colon thyroid and breast cancer as well as certain pediatric tumors. 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. 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 druginduced side effect.    Equally important the response was longlasting 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 said Dr. Laetsch who investigates the use of tumor molecular profiling to guide therapy in UT Southwesterns Pediatric Hematology and Oncology Division.    A next step in the research is a clinical trial involving a similar drug for those patients who developed resistance. Dr. Laetsch will be the national leader for that clinical trial in children.        The larotrectinib research was supported by Loxo Oncology Inc. the National Institutes of Health the Cancer Prevention and Research Institute of Texas the National Center for Advancing Translational Sciences and Alexs Lemonade Stand Foundation. Dr. Laetsch is a paid consultant for Loxo Oncology Inc.    The Harold C. Simmons Comprehensive Cancer Center is the only NCIdesignated Comprehensive Cancer Center in North Texas and among just  U.S. cancer research centers to be designated by the NCI as a National Clinical Trials Network Lead Academic Participating Site. UT Southwestern Medical Center is recognizing its th year this year.    About UT Southwestern Medical Center    UT Southwestern one of the premier academic medical centers in the nation integrates pioneering biomedical research with exceptional clinical care and education. The institutions faculty has received six Nobel Prizes and includes  members of the National Academy of Sciences  members of the National Academy of Medicine and  Howard Hughes Medical Institute Investigators. The faculty of more than  is responsible for groundbreaking medical advances and is committed to translating sciencedriven research quickly to new clinical treatments. UT Southwestern physicians provide care in about  specialties to more than  hospitalized patients  emergency room cases and oversee approximately . million outpatient visits a year."