siddartha mukherjee. we decided to bring him back for a second round. joining me from new york elliott sandler and dr. mukherjee. did you know throughout your life your brother's role in history? >> i had no idea until actually recently until the book came out. i had no idea. >> you dedicated the book to robert sandler. there's a lot of patients in your book, you told their stories. why robert in particular? >> he was part of the first group of children to be treated by chemotherapy in 1947. he had a brief response to the drug and relapsed and died after it. what's amazing about the story is by adding more combinations of the same kinds of drugs, eventually, this disease that