Kevin Murphy and Robert Topel write,

From 1970 to 2000 gains in life expectancy added about $3.2 trillion per year to national wealth, with half of these gains due to progress against heart disease alone. Looking ahead, we estimate that even modest progress against major diseases would be extremely valuable. For example, a permanent 1 percent reduction in mortality from cancer has a present value to current and future generations of Americans of nearly $500 billion, while a cure (if one is feasible) would be worth about $50 trillion.

UPDATE: Thanks to commenter Dennis for finding a link to the paper.