In a study from the American Cancer Society, researchers report that the cancer mortality rate dropped by 29% between 1991 and 2017, a trend possibly explained by improved treatments and public-health initiatives to reduce smoking—but access to quality care and the lack of effective screening methods for some cancers remain hurdles.

The overall mortality rate from cancer declined by 29% in the United States between 1991, when it peaked, and 2017—reducing the number of lives lost to cancer by an estimated 2.9 million—according to a recent analysis (CA Cancer J Clin 2020;70:7–30). Although it's tempting to ascribe the mortality reduction to recent treatment advances, such as the introduction of immune-checkpoint inhibitors, the reality is more complex.

The largest drop in age-adjusted mortality was seen between 2016 and 2017, making speculation about the role of the newest therapies particularly alluring, but the overall pattern is perhaps more noteworthy than the 2.2% decline. “It's very much a continuation of a long-term trend,” says Kathy Cronin, PhD, MPH, deputy associate director of the NCI Surveillance Research Program.

These reductions have primarily been driven by a decrease in lung cancer deaths. “If you take lung cancer out [of the analysis for 2016 to 2017], that 2.2% goes down to 1.4%,” says lead author Rebecca Siegel, MPH, of the American Cancer Society. Lung cancer is the leading cause of U.S. cancer mortality, accounting for more deaths than breast, colorectal, and prostate cancers combined, explaining its outsized influence on cancer survival.

In the 5 years leading up to 2017—even prior to the approval of immunotherapies—the lung cancer death rate fell by about 4% per year. Reduced incidence due to decreases in smoking accounts for part of the shrinking death rate, but improved treatments, including new surgical options, and other factors may play a role. Survival following lung cancer diagnosis is increasing, which hints at the importance of treatment advances. However, the study cannot pinpoint causality.

Major strides have also been made in treating pediatric cancers, with mortality slashed by 68% for pediatric cancers and 63% for adolescent cancers since 1970. “It's not new therapies,” says Siegel—instead, the drop is primarily attributable to optimizing dosages and combining existing chemotherapies. The greatest success has been in childhood acute lymphocytic leukemia, which now has a remission rate nearing 100%. This steady decline comes even as the incidence of childhood and adolescent cancers has increased by about 0.7% per year since 1975, for unknown reasons.

In contrast, survival rates for cancers of the uterine corpus and cervix have not declined since the mid-1970s. Human papillomavirus vaccination will likely drive down cervical cancer incidence and mortality, but the lack of new treatments and effective screening methods for other uterine cancers does not portend mortality improvements. “We're going to continue to see increases in endometrial cancer incidence and mortality,” says Ashley Felix, PhD, MPH, of the Ohio State University Comprehensive Cancer Center in Columbus. Incidence is likely to increase due to factors such as reduced hysterectomy rates, declining pregnancy rates, and rising obesity rates—the last of which is a contributor to many other cancers.

Further progress in cancer treatment may help maintain the downward trend in mortality, but advances may also be possible by other means. “There's much more opportunity to accelerate the progress by ensuring that all people, especially those who are low income, have access to high-quality care,” says Siegel.

“I think the treatments are important, but I think also that the public-health initiatives to reduce smoking are really playing an important role, too,” Cronin adds. –Nicole Haloupek

For more news on cancer research, visit Cancer Discovery online at http://cancerdiscovery.aacrjournals.org/CDNews.

©2020 American Association for Cancer Research.
2020
American Association for Cancer Research.