Simplify the following text for a Grade 8 native English-speaking person.
Original: With the exception of William Coley who in the late 19th century felt that the rate of cure after surgery had been higher before asepsis ( and who injected bacteria into tumors with mixed results ) , cancer treatment became dependent on the individual art of the surgeon at removing a tumor .
Simplified: Cancer treatment became dependent on the individual art of the surgeon at removing a tumor , except for William Coley . In the late 1800s , Coley felt that the rate of cure after surgery had been higher before asepsis .