History
Viltolarsen was developed by Nippon Shinyaku and the NCNP based on pre-clinical study conducted by Toshifumi Yokota and colleagues, and evaluated in two clinical studies with a total of 32 participants, all of whom were male and had genetically confirmed DMD. The increase in dystrophin production was established in one of those two studies, a study that included sixteen DMD participants, with eight participants receiving viltolarsen at the recommended dose. In the study, dystrophin levels increased, on average, from 0.6% of normal at baseline to 5.9% of normal at week 25. Trial 1 provided data for evaluation of the benefits of viltolarsen. The combined populations from both trials provided data for evaluation of the side effects of viltolarsen. Trial 1 was conducted at six sites in the United States and Canada and Trial 2 was conducted at five sites in Japan. All participants in both trials were on a stable dose of corticosteroids for at least three months before entering the trials.The U.S. Food and Drug Administration (FDA) concluded that the applicants data demonstrated an increase in dystrophin production that is reasonably likely to predict clinical benefit in people with DMD who have a confirmed mutation of the dystrophin gene amenable to exon 53 skipping. A clinical benefit of the drug has not been established.
It is the third most common intestinal tumor in cats, after lymphoma and adenocarcinoma.Diagnosis and treatment are similar to that of the dog. Cases involving difficult to remove or multiple tumors have responded well to strontium-90 radiotherapy as an alternative to surgery. The prognosis for solitary skin tumors is good, but guarded for tumors in other organs. Histological grading of tumors has little bearing on prognosis. References
External links

Mast Cell Tumors from The Pet Health Library
Mast Cell Tumors in Dogs from Pet Cancer Center
Mast Cell Tumors in Cats from Pet Cancer Center