There's a worrisome problem with Obama's 'moonshot for cancer' plan

In his final State of the Union address on Tuesday, President Obama suggested that Vice President Biden would lead what he called a "moonshot to cure cancer."

It's a noble goal. But it's also over-optimistic. And that's important to keep in mind when we're designing treatments for a disease which claims an estimated 8 million lives around the world each year.

Cancer is different from many genetic diseases, such as sickle cell or Huntington's, in that it is not linked with a few specific, identifiable genes. Instead it is the result of a whole bunch of mutations, tens of hundreds of tiny twists and pinches in our genes. These mutations are constantly changing and evolving, becoming increasingly resistant to our drugs. And genetics, of course, is not the only cause of cancer - environmental and behavioral factors matter.

Still, we've managed to curb the incidence of many types of cancer in the past few decades, either through behavioral changes (after 50 years of anti-tobacco campaigns in the US, for example, rates of lung cancer have plummeted) or vaccines (we can prevent new cases of human papillomavirus, which causes most cervical cancer, and Hepatitis B, which causes most cases of liver cancer). President Obama's Precision Medicine Initiative aims to build on these efforts and treat existing cancers more efficiently.

There are even some types of cancer we can cure with surgery (in the case of some skin cancers) or a combination of several drugs and treatments (such as with some cases of Hodgkin's lymphoma or leukemia).

But there are still many types we can't.

"There will be a sizable portion of cancers we can't get rid of," Harold Varmus, director of the National Cancer Institute, said at a talk last year at Columbia University. "We're not going to eliminate cancer as a disease."

Why?

To say each cancer tumor is unique would be an understatement. "Virtually every tumor looks different from every other tumor," Varmus said. That makes designing drugs to beat them difficult. Many new treatments work only for a tiny subsection of patients, those with a specific subtype of one particular kind of cancer. These are exciting developments, but they don't begin to move the needle on treating - not to mention curing - cancer as a whole.

Plus, among the various genes involved in cancer, some are what Varmus calls "drivers," meaning they have an active role in spreading the disease throughout the body, while others are merely "passengers," meaning they make only neutral changes to the genome.

Think of trying to design a net for a species of sea creature that constantly changes its size and shape (and also sometimes decides to live on land instead of in water).

No matter how advanced your net, some monsters will still be uncatchable.

As if that weren't enough, some of the drugs used by doctors in recent decades can actually encourage the cancer to develop resistance to them. When cancer cells detect the presence of these "targeted drugs," they do everything they can to survive, often mutating into forms that can't be defeated by the drugs.

This doesn't mean doctors and scientists are not making progress. They are. Still, cancer as a whole will probably never completely disappear - and that's a reality of which we should be aware.