It's probably more than 3 years for the people actually afflicted with cancer. The "3 year" figure is likely influenced by the fact that the majority of people never develop cancer, but rather an incredibly large minority of around 39 percent (as opposed to something like heart disease, where around 86 percent of people aged 80+ are believed to have some degree of heart disease). My paternal grandmother was diagnosed with breast cancer in 1980 at the age of 56 or 57. Treatment was successful and she never developed any other form of cancer for the remainder of her life; she died in 2014 just shy of her 91st birthday, and was in good health the entire time aside from her final year where she struggled with cardiovascular dementia (she was lucid at 89 but had some problems at 90). If she'd died from her cancer in 1980, she would have lost not 3 years, but 34.