At first glance, it appears that little will change between now and 2040 when it comes to the types of cancers that people develop and that kill them, a new forecast shows.

Breast, melanoma, lung and colon cancers are expected to be the most common types of cancers in the United States, and patients die most often from lung, pancreatic, liver and colorectal cancers, according to the latest projections.

But beneath the surface, changes are occurring due to a shift in the nation's top causes of cancer, and those trends are likely to affect treatment and research for decades, experts say.

Lung cancer cases and deaths are expected to continue to decline, likely due to the success of anti-smoking campaigns. However, deaths from obesity-related cancers—pancreas, liver, colon—are projected to hold steady or increase, the researchers said.

"We've already seen a little bit of a shift from smoking-related cancers to an increase in the proportion of cancer cases and deaths that are related to obesity," noted Kim Miller, a scientist with the American Cancer Society's surveillance and health equity team, who reviewed the new study.

In general, researchers expect that cancer cases will continue to increase overall in the United States as the population becomes larger and grayer, said senior researcher Dr. Kevin Nead. He's an assistant professor of epidemiology with the University of Texas MD Anderson Cancer Center's division of cancer prevention and population sciences.

"Our population is going to get bigger, and we're going to see more and more cancers. I think no matter what happens in the future, we're going to see more cancers," Nead said.

However, Miller said, cancer deaths have been declining since 1991 and are expected to continue to fall in the future.

"A large proportion of that drop is due to lung cancer death rates very, very rapidly declining, but we're seeing progress for a lot of cancers and I think that's important to keep in mind," Miller said.

For this study, Nead and his team combined cancer incidence and death rates with updated demographic data from 2016 to project cancer cases and deaths out to 2040. They published their findings online April 7 in JAMA Network Open.

Overall, the most frequent cancer types are expected to change slightly due to an increase in melanoma cases, making it the second most common cancer by 2040. Breast cancers are projected to be the most common, with lung cancer third and colon cancer fourth.

"Melanoma has moved up, and we don't necessarily know exactly why that is," Nead said. More people might be exposing themselves to the sun's UV rays, or there might be improved detection of the early stages of melanoma skin cancer.

Prostate cancer is expected to drop to the 14th most common cancer by 2040, possibly due to changes in screening guidelines, the researchers said.

As far as cancer deaths, lung cancer is expected to continue to be the leading cause of cancer-related deaths in 2040, but with an overall declining number of deaths, the report said.

At the same time, pancreatic and liver cancers are expected to surpass colon cancer to become the second and third most common causes of cancer-related death.

"The steady increase in gastrointestinal cancers is troubling," Nead said. "Seeing cancers creeping up where I think we still have some work to do in prevention, I think that's a little more scary than situations where we have good prevention and surveillance, we just need to use it better."

There aren't good screening tools for either pancreatic or liver cancer, and colon cancer screening is underutilized, with one in three people who meet guideline recommendations for such screening not getting it done, according to the report.

"A lot of the things we have in cancer over time in our paper, and in others, really reinforces the value of putting resources into screening and prevention, which isn't always as exciting as new treatments that cure cancers," Nead said. "But the best way to not have a cancer or die from a cancer is to not get the cancer in the first place."

Although breast cancer will remain a common type, deaths from breast cancers are projected to decline from 42,000 in 2020 to 30,000 in 2040, consistent with the 40% decline in deaths since 1989, the study authors said.

However, both Nead and Miller cautioned that these projections could easily change with advances in treatment or preventive measures, and should be taken with a grain of salt.

Even this list itself could change the future, by redirecting efforts toward cancers that are trending upward, Nead noted.

"We can allocate resources to hopefully make our projections inaccurate," Nead said. "If we know we're going to have a big problem area, well, 20 years is a long time. Maybe some research funding allocations can go toward breakthroughs in that area, hopefully those breakthroughs happen, and our projections aren't accurate."

—Dennis Thompson Healthday Reporter