A 67-yeаr-оld wоmаn undergоes routine mаmmography. Screening detects a small, slow-growing tumor that her oncologist describes as "clinically insignificant" — statistically unlikely to cause symptoms or affect her lifespan. Because it has been detected and labeled as cancer, she undergoes surgery and radiation, experiencing significant side effects. Her oncologist later acknowledges the tumor would almost certainly never have harmed her. What does this case illustrate about a limitation of cancer screening?