Congenital mesoblastic nephroma (CMN) is a rare tumor most often seen in infants. It is the most common kidney tumor in newborns under 1 month old. In about 10 to 20 percent of cases, it can be detected before the baby is born. At MSK Kids, we treat most infants with CMN using surgery alone. For those who need other or additional treatment, we use a unique approach that includes the drug larotrectinib (VITRAKVI). This medicine blocks a protein called NTRK and can treat inoperable CMN tumors caused by the NTRK3 and ETV6 genes fusing together. MSK researchers played a big role in the US Food and Drug Administration’s approval of larotrectinib.