A record drop in the rate of U.S. cancer deaths, announced Wednesday, has Minnesota specialists encouraged that advances in medical treatment are having an impact alongside preventive measures such as anti-smoking campaigns and colonoscopy screenings.

The American Cancer Society reported Wednesday that the U.S. cancer death rate has declined 29% since 1991, and 2.2% in just one year, from 2016 to 2017 — the largest one-year drop ever recorded.

While increased cancer screenings help explain the gradual, decadeslong trend, they alone couldn't have caused such a dramatic change in one year, said Matt Flory, an analyst for the Cancer Society's North region, based in Eagan.

"Do people really think smoking [habits] changed that much year over year?" he said. "I think that's a signal that it's not just smoking, but that it's advances in therapy, too."

New treatments include the use of "checkpoint inhibitor" drugs over the past decade, particularly in the treatment of a form of skin cancer known as melanoma, that prevent cancer cells from eluding the human immune system. Testing to identify specific molecules and genetic mutations behind certain cancers has helped doctors create treatments tailored to individual patients, and such testing is becoming cheaper and more widely used.

The overall decline was driven largely by progress in preventing and treating melanoma and lung cancer, though the latter still kills more people than breast, prostate, colorectal and brain cancers combined, the Cancer Society data showed.

Progress has been incremental, said Dr. Douglas Yee, director of the University of Minnesota's Masonic Cancer Center. A new treatment for breast cancer, for example, might work for only the 3% of patients with certain genetic mutations. New guidelines have refined standard chemotherapies so they work better, and new technology has focused radiation beams so they more tightly target tumors rather than healthy tissue.

"Each one may benefit only a small group, but in aggregate, they decrease mortality," Yee said. "The yardage gained is sort of small increments. You don't get the Hail Mary pass that everyone would like."

The melanoma mortality rate began declining by 7% per year among men and women ages 20 to 64, and by 5% to 6% per year in individuals 65 and older, following federal approval in 2011 of two new therapies for the most severe, metastatic versions of the skin cancer.

"That was the largest decline in cancer mortality that we saw," said Rebecca Siegel, director of surveillance research at the American Cancer Society and lead author of the organization's report, which was published online in CA: A Cancer Journal for Clinicians. "And what made it so dramatic is that for people 65 and older, melanoma mortality rates were actually increasing in the 2000s."

Harnessing T cells

Recent declines in cancer deaths also reflect the launch of immunotherapies that have helped some patients by enlisting so-called T cells to kill their tumors. Both the Mayo Clinic and University of Minnesota have launched CAR-T therapy programs that harvest T cells from patients' immune systems, boost their cancer-fighting properties, and then infuse them back into the patients.

Screening and prevention efforts have played a role, especially in Minnesota. The male cancer death rate in Minnesota for the five-year period ending in 2017 was 179 per 100,000 people, compared with the U.S. rate of 189.3. The state's breast cancer death rate of 10.8 per 100,000 women was among the lowest in the nation.

National survey data showed that 73% of Minnesotans 50 and older were up to date on screenings for colon cancer, compared with a national screening rate of 67%. Flory said recent gains in colon cancer screenings have resulted in more polyps being found in patients' intestines before they reach cancerous stages.

"Everyone is looking for the silver bullet" that caused cancer deaths to drop, he said. "It's a little bit of everything."

National cancer experts urged caution in celebrating the results. Declines in the rates of death from breast and colorectal cancers have begun to taper off, likely due to the rising rate of obesity among Americans, as well as significant racial and geographic disparities in prevention and treatment programs. The decline in the rate of prostate cancer deaths has halted entirely.

Studies have found that obesity, unhealthy diets and a lack of physical activity are associated with metabolic and hormone abnormalities and with chronic inflammation, which may help explain the link to cancer. Controlling these factors could help jump-start declines in cancer incidence and mortality rates once again, said Timothy Rebbeck, an epidemiologist at Harvard University and the Dana-Farber Cancer Institute.

Still a killer

Cancer remains the second leading cause of death after heart disease in both men and women nationally. The American Cancer Society predicts that in 2020 there will be about 1,806,590 new cancer cases and 606,520 cancer deaths.

"We are still dealing with the effects of cigarette smoking from the 1960s and '70s in today's population," said Dr. Otis Brawley, an oncologist at Johns Hopkins University and former chief scientific officer at the American Cancer Society. Because there is a lag between exposure and cancer diagnosis, people who stopped smoking may develop lung cancer years later. But these rates should continue to decline, Brawley said.

Renewed progress in reducing mortality for breast and other cancers might require organizing and understanding the wealth of information coming from diagnostic and molecular tests, said Dr. Edward Greeno, chief of cancer care for M Health Fairview, based in Minneapolis.

Right now, testing is producing more genetic and molecular information than doctors can effectively analyze and use in treatment planning, he said. "It's not yet information overload, but you can see we're at the beginning of a really steep slope."

In some cases, doctors know of some genetic mutations causing cancers, but treating them one at a time might be ineffective compared to treating the combinations of them that are actually at work, he said.

Greeno said research also will help by producing more antibody therapies that either target tumors themselves or identify unhealthy cancer cells so that chemotherapy drugs can target them and spare healthy cells from their toxic effects.

"It's all of these not-very-sexy incremental improvements that we make" that are helping, he said. "And some of it frankly is learning not to use some things when we shouldn't, too."

The New York Times contributed to this report.

Jeremy Olson • 612-673-7744