It’s been almost 40 years since President Richard Nixon declared the “War on Cancer” with the signing of the National Cancer Act of 1971 and the allocation of $100 million to fight the disease.

The government now spends almost $5 billion a year to battle cancer and it appears that 38 years after the war was declared, the U.S. medical community is finally gaining the upper hand on some of the most common types of cancer.

Improvements in cancer screening and better treatments have resulted in steady declines in cancer death rates over the past three decades, U.S. researchers said on Thursday.

Slideshow: Surviving Cancer

Younger adults — those aged 35 to 45 years old — have experienced the steepest declines in cancer death rates, but all age groups have shown some improvement.

"Essentially, the younger you are, the faster your rates are declining," said Dr. Eric Kort of the Helen DeVos Children's Hospital in Grand Rapids, Michigan, whose study appears in the journal Cancer Research.

U.S. government estimates suggest there had been little improvement in cancer death rates throughout the 20th century, with rates only beginning to improve in the mid-1990s, Kort said. But that does not tell the whole story, he added.

"The way that these statistics are traditionally reported is they have averaged all of the age groups together to get a composite rate," Kort said in a telephone interview with Reuters.

"The problem with that is because most cancer deaths occur in older Americans, the average heavily emphasizes the experiences of older people. It's like watching the caboose of the train to tell when the train is changing direction," he said.

The average survival rate for all cancers combined increased almost 20 percentage points from 1975 to 2000 from 49.84 percent to 67.16 percent, according to the National Cancer Institute.

But for many of the most common cancers, the survival rates are much higher.

In childhood cancers, advances in treatments for leukemia and lymphoma mean many more people can survive cancers that were once considered a death sentence.

The 5-year survival rates for all childhood cancers combined increased from 58.1 percent in 1975–77 to almost 80 percent 1996–2003. This improvement in survival rates is due to significant advances in treatment, resulting in a cure or long-term remission for a substantial proportion of children with cancer.

And better screening for cancers that occur in older age, such as mammography for breast cancer and colonoscopy for colon cancer are spotting cancers at an earlier stage, when they are easier to treat.

Survival rates for breast cancer, for example, increased from 75.33 percent in 1975 to 90.55 percent in 2000, according to the National Cancer Institute. Survival rates for colon cancer increased from 49.43 percent in 1975 to 66.03 in 2000, while prostate cancer survival rates increased more than 30 percent — from 66.95 percent in 1975 to 99.21 percent in 2000.

Lung and bronchus cancer remain the hardest to treat, however, and survival rates for those cancers are still relatively low – increasing from 11.90 percent in 1975 to just 16.19 in 2000.

Kort's team looked at improvements in cancer deaths among groups of individuals born in five-year intervals starting in 1925.

Using that method, Kort said, "Everyone born since the 1930s has enjoyed a decreased risk of cancer death, at every age."

People in the youngest age group — those aged 35 to 45 — had a greater than 25 percent decline per decade in cancer deaths, he said.

Kort said cancer prevention — including smoking cessation efforts — have played an important role in these trends.

"We're also benefiting in profound ways from progress we're making in early detection and better treatments. Some of these advances benefit younger people first," he said.

Cancer remains the No. 2 killer of Americans, with about 560,000 deaths annually, topped only by heart disease, according to the American Cancer Society.

Reuters contributed to this report.