When You Hear Hoofbeats, Look for Horses, Not Zebras—Reply

In Reply After the publication of our study identifying anaplastic lymphoma kinase (ALK) rearrangements in peritoneal mesothelioma,¹ we read the Letter by Kataoka et al with skepticism. Because both peritoneal mesothelioma and primary peritoneal carcinoma are rare intra-abdominal tumors, Kataoka et al wonder whether our 3 cases of ALK-rearranged peritoneal mesothelioma may represent misdiagnoses and are instead primary peritoneal carcinomas with ALK rearrangement. We address their concern as follows.