As I learn more pathology, I see the uncertainties inherent in medicine’s definitions. Cancer is not merely cancer but a product of philosophy, linguistics, and probability. I have been surprised to learn how much the undergraduate medical curriculum downplays the importance of epistemology on disease screening, overdiagnosis, and overtreatment. As a medical student, talk about these topics was theoretical physics—impossible to connect to real practice. As a pathologist, my definition of disease has become an atomic bomb leading directly to patient care and well-being.