In cancer studies, the Kaplan-Meier estimator is crucial for several reasons. Firstly, it allows researchers to compare the survival rates between different treatment groups. Secondly, it helps in identifying factors that might affect patient survival, such as age, stage of cancer, or type of treatment. Thirdly, it provides a visual representation of the survival experience of a cohort of patients, making it easier to understand the impact of the disease and treatment.