New laws in recent years cut the maximum workweek of physicians to 80 hours/week. Before then it was routine for young physicians to work upwards of 100-120 hours/week. I think we can all agree that stress and lack of rest is definitely detrimental to health.
I don't think your statement about cancer is completely true. As a whole, it is far better to get treatment for cancer, especially ones that have high cure rates, i.e. certain lymphomas and skin cancers. Howeverm for very advanced cancers, or any other chronic severe illness like heart failure, liver cirrhosis, emphysema, it has been shown that hospice care just for comfort without treatment is not only cheaper and offers better quality of life, it also adds on a significant amount of life. It's not on the order of decades but certainly months more than those who choose aggresive treatment.