Death rates and new diagnoses of cancer are dropping, but cancer remains one of the leading causes of death in the U.S., despite nearly $100 billion in research to fight the diseases since 1971.

Susan Gapstur of the American Cancer Society said the investment since the 1971 National Cancer Act has been matched by other companies.

All this has resulted in some progress, she said. From 1991 to 2006, the death rate from cancer dropped nearly 16 percent. Over the last decade, the rate of new diagnoses has dropped almost 1 percent.

Gapstur and other authors of a commentary said the biggest factor in the drop is a reduction in smoking.

However, there were still almost 1.5 million cases of cancer in the U.S. in 2009, with more than 560,00 deaths. That makes cancer the second-leading cause of death.

She said about half of men and about one-third of women will be diagnosed with cancer in their lifetimes, and those numbers are going up as people tend to live longer.

"The war on cancer has become considerably broader and more complex over time. Cancer is a [many-formed], complex and highly adaptable disease. Although progress has been made in reducing cancer mortality rates, the number of persons affected by cancer will increase due to an aging population unless progress in cancer prevention and reducing incidence rates are accelerated," they wrote. "Nevertheless, advances and insights accumulated during the last 40 years provide a strong foundation on which to continue the fight against cancer."