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Cancer death rates have declined steadily over the past several decades, falling by nearly a third since the early 1990s, according to a report published Wednesday by the American Cancer Society.

From 1991 to 2017, overall cancer deaths dropped by 29 percent, estimated at nearly 3 million avoided deaths.

Declines in mortality for four major cancers — breast, colon, lung and prostate — contributed largely to the decadeslong drop, with improved lung cancer survival playing a particularly significant role, according to the society's annual look at cancer death rates, published in CA: A Cancer Journal for Clinicians.

Deaths from lung cancer dropped by 51 percent among men since the early 1990s and by 26 percent among women since the early 2000s.

The report also credits drops in lung cancer mortality for a 2.2 percent dip from 2016 to 2017 — the largest decline of cancer deaths in a single year ever reported.

Doctors attribute the success in part to lower smoking rates but also to significant advances in treatment.

Major medical advances

"The years we have been investing in basic science of cancer therapeutics [are] now starting to pay off," said Dr. Patrick Hwu, division head of cancer medicine at MD Anderson Cancer Center in Houston.

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Hwu, who was not involved with the new report, credited targeted therapies, which are drugs that work to eliminate the circuitry that turns on cancer cells.

Another of the biggest advances, experts said, has been the development of immunotherapies such as Keytruda, also known as pembrolizumab. It uses the body's immune system to fight tumors, and it is approved for lung cancer and melanoma, the most dangerous form of skin cancer.

The American Cancer Society report also found rapid declines in melanoma death rates, up to 7 percent a year from 2013 to 2017 among adults, also attributable to new treatments.

In 2011, the Food and Drug Administration approved two key drugs to treat melanoma: ipilimumab and vemurafenib.

"We're actually seeing the effect of those drugs reflected in the overall melanoma death rate," said Rebecca Siegel, scientific director of surveillance research at the American Cancer Society and an author of the new report. "That's really exciting."

Physicians are seeing it in practice, as well.

"In the past decade, how we treat invasive melanoma has evolved so unbelievably rapidly that it is, for some, becoming more of a chronic disease than a death sentence," said Dr. Adam Friedman, a professor of dermatology at the George Washington School of Medicine and Health Sciences in Washington, D.C.

More work ahead

Still, not all cancers saw improved survival rates. For example, the report did not find any significant improvements in deaths from cervical cancer, a disease that is not only preventable with a vaccine but is also easily detected through early screening.

However, in 2017 alone, 10 women in their 20s and 30s died every week in the United States from cervical cancer.

Among the report's other findings:

A 40 percent drop in the breast cancer death rate from 1989 to 2017.

A 52 percent drop in the prostate cancer death rate from 1993 to 2017.

A 53 percent drop in the colorectal cancer death rate since 1980 among men and a 57 percent drop since 1969 among women.

Despite the decline in death rates, lung cancer remains the leading cause of cancer deaths by far, killing more people than breast, colorectal and prostate cancers combined.

The American Cancer Society projects that 606,520 people will die of cancer in the United States in 2020 and that more than 1.8 million new cancer cases will be diagnosed.

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