• The rate of cancer deaths in the U.S. fell by a record 2.2% between 2016 and 2017, extending a nearly three-decade long decline largely driven by fewer Americans smoking cigarettes as well as better detection methods and new treatments.
• Since 1991, when the cancer death rate peaked, the American Cancer Society has recorded annual reductions of 1.5% per year on average. Accelerating declines in deaths from lung cancer led to the drop between 2016 and 2017, which is the largest single-year decrease observed by the group.
• “The news this year is mixed,” said Rebecca Siegel, lead author of the report and director of surveillance research at the American Cancer Society, in a statement on this year’s report, issued Wednesday. “The exciting gains in reducing mortality for melanoma and lung cancer are tempered by slowing progress for colorectal, breast and prostate cancers, which are amenable to early detection.”

Lung cancer has been the most common cause of cancer death for decades, ranking above tumors of the prostate, colorectal and breast.

While that’s still the case, sharp declines in the number of Americans dying from lung cancer contributed to 2017’s record drop in the U.S. cancer death rate.

Between 1991 and 2017, the death rate has fallen by 29%, according to ACS, resulting in nearly 3 million fewer deaths than would have occurred had rates remained at their 1991 peak.

Smoking declines as well as improved detection of cancers like those of the breast and prostate have driven much, if not most, of that shift. But within those broader trends, advances in treatment have changed the outlook for several cancers, most notably certain types of lymphoma and leukemia.

More recently, the introduction of Bristol-Myers Squibb’s immunotherapy Yervoy (ipilimumab) as well as Roche’s targeted drug Zelboraf (vemurafenib) have pushed the death rate for melanoma sharply lower. Between 2013 and 2017, the rate fell by 7% annually, up substantially from the 1% per year recorded by ACS from 2006 to 2010.

And while researchers did not explicitly test whether declining lung cancer death rates were due to newly introduced drugs like Merck & Co.’s Keytruda (pembrolizumab), researchers suggested clinical advances could be playing a role.

Over the five-year span between 2013 and 2017, lung cancer death rates declined by 5% in men and 4% in women, compared to the 3% and 2% rates measured between 2008 and 2013, researchers wrote.

Even so, lung cancer caused more deaths in 2017 than breast, prostate and colorectal cancers taken together. And five-year survival rates remain low, due in part to most cases being diagnosed when tumors have already metastasized.

“I feel comfortable making the prediction that the trend in lung cancer will continue as immunotherapy moves into the adjuvant and neoadjuvant realms,” wrote Otis Brawley, a professor at Johns Hopkins University and former chief medical and scientific officer of the American Cancer Society, in a editorial published by The Cancer Letter.

Adjuvant and neoadjuvant refer to the use of drugs prior to or immediately following surgery.

Brawley also noted the Food and Drug Administration’s approach to approving new cancer drugs using trial endpoints like progression-free survival or response rates could be backed up by improved death rates.

“As we look at the data for [non-small cell lung cancer], we can argue that the careful and rigorous use of validated intermediate endpoints in clinical trials has itself been validated,” wrote Brawley.

Yet drawing a direct line between falling lung cancer death rates and new treatments is complicated and susceptible to statistical errors.

Peter Bach, the director of Memorial Sloan Kettering’s Center for Health Policy and Outcomes, said on Twitter that further study would be needed to distinguish between potentially conflicting trends affecting death rates.

“When other deaths that share cancer risk factors rise, it mathematically reduces cancer mortality rates,” he wrote. “Deaths from opiates and suicides, both rising, share social, economic and behavior risk factors [with] cancer.”