Scientists are at work on vaccines that might someday stop cancer.

How long do you expect to live? That's probably not a question you care to think about every day, but you can probably expect to live considerably longer than the generations that preceded you. A baby born in the United States today can expect to live to over 77 years of age, according to the CIA's World Fact Book. One hundred years ago, it was unusual for someone to live that long. The life expectancy of all American babies born in 1900 was just 49 years. Today, more than 27 percent of the American population is over 50.

The point of these statistics is to illustrate how the health of the world, not just of the United States, is improving at a remarkable rate. Today, there is a larger percentage of senior adults than the world has ever seen. So, what's allowing us all to live longer than ever before? The most obvious reason is the amazing amount of medical technology developed in the 20th century. Scientists have developed medicine and equipment that enable us to fight off disease more effectively. Penicillin (1928), measles vaccine (1953), polio vaccine (1954) and insulin (1920s) are just a few of the many medical discoveries made in the last century.

Among the most notable achievements in that time was the eradication of polio and smallpox through vaccines. Today, scientists continue their search for vaccines to prevent other diseases. Possibly the most exciting achievement of this century will be the discovery of a universal cancer vaccine. Scientists are on the verge of developing such a vaccine that will save millions of lives annually when it's discovered. In this edition of How Stuff Will Work, we will take a look at current cancer treatments and types of cancer treatments in development.