Cancer researchers are closer than ever to achieving their long-held dream of turning the disease from a death sentence to a chronic illness. This would be a remarkable scientific achievement. But while people may soon routinely live decades with their cancer in remission or even cured, they will not become immortal. Most will eventually suffer from some other debilitating condition and require a period of long-term supports and services.

And as a society, we are not ready. Our system of social supports is already failing to keep up with medical technology. We don’t have the money to buy the assistance we need today, much less what we’d need to live those extra years. As a result, advances in cancer research may prolong our lives but not necessarily improve our long-term quality of life.

While oncologists are still far from their goal, they are making enormous progress. A major conference last week highlighted just how far the research has come. Here are just two examples:

Drugs that trigger the body’s own immune system to attack cancer cells, often in combination with other therapies, are showing positive results for cancers that until recently were thought untreatable such as melanoma, non-small cell lung cancer, and certain blood cancers.

At the same time, the ability to sequence genes, quickly and at low-cost, is fundamentally changing how oncologists look at cancer. Where they once focused almost exclusively on the initial location of a tumor, they are beginning to categorize cancers based on common mutating genes.  That opens the door to a whole range of new, highly customizable, drug therapies.

We have already turned many heart conditions into manageable chronic disease. With stents, devices, and drugs, cardiac patients now live long, relatively normal lives. We have done it with some forms of breast cancer. As a result of these and other advances, when Congress created Medicare a half-century ago life expectancy in the US at age 65 was about 14 years. Now it is almost 20 years. That’s extraordinary.

But what are the consequences of these achievements?

Hundreds of thousands or perhaps millions of people who might have died young will now live to old age. Many will survive long enough to contract Alzheimer’s disease or some other form of dementia—conditions that most commonly begin showing symptoms only after age 80. Or they will break a hip, or suffer from severe arthritis, or pulmonary disease.  We can’t cure everything.

I’m not trying to kill the buzz. Medical advances in cancer and heart disease are wonderful. But they only highlight how unprepared we are for increasing numbers of people who will live extremely long lives.

There was story in the paper the other day about a 92-year-old women who ran a marathon. Good for her, but most of us won’t make it to the finish line in as good a shape as she is. And one day even she may become frail and need personal assistance to live the best life she can.

For the most part, the health system doesn’t even think about the man who beats melanoma at 60 and lives to get dementia at 85. Its focus remains on acute episodes, not chronic illness. Medicare, which will foot the bill for many of those enormously expensive anti-cancer therapies, won’t pay a dime for a long-term home care aide or a nutritious meal.

We want to live forever (or at least for an extra decade or two). And medical science may make it possible. But what will we do then? Who will take care of us? And how?