Not being familiar with acute lymphoblastic leukemia (ALL), I checked out W'pedia. Turns out that the current survival rate for this cancer that is commonly diagnosed around this child's age is 90%. There's no guarantee this child would be among the 90% rather than the 10%, of course.
But when I perused the chemotherapy agents commonly used in treatment of ALL, the name of one, vincristine, stood out. One of my children was on vincristine for six months for a different disease. At the time she was 2 years old. Other than losing her hair after a month or two and thoroughly disliking the injection process, she really didn't have much other noticeable reaction. That was some 30 years ago, she's clear of the disease, and doing well (her hair freaks out hairdressers where she lives in China, because her hair is curly and the hairdressers aren't sure what to do).