Adults under age 50 have been developing breast cancer and colorectal cancer at increasingly higher rates over the last few decades, and alcohol use may be one factor driving the trend, according to a scientific report published on Wednesday.

The report, by the American Association for Cancer Research, highlights scientific breakthroughs that have led to new anticancer drugs and improved overall survival.

But the authors also described a troubling pattern: Even as cancer death rates have declined, the overall incidence of several cancers has been rising inexplicably, with an especially alarming increase among younger adults in cancers of the gastrointestinal system, like colorectal cancer.

The report estimates that 40 percent of all cancer cases are associated with modifiable risk factors. It recommends reducing alcohol consumption, along with making lifestyle changes such as avoiding tobacco, maintaining a healthy diet and weight, exercising, avoiding ultraviolet radiation and minimizing exposure to pollutants.

The authors called for raising awareness through public messaging campaigns and adding cancer-specific warning labels to alcoholic beverages.

The recommendations come amid a radical rethinking of the putative health benefits of moderate alcohol consumption, which for years was considered to be protective against heart disease.

Just last month, a large study that followed more than 135,000 older British adults for over a decade found that moderate and light drinkers did not benefit from a reduction in heart disease when compared with occasional drinkers.

And both moderate and light drinkers experienced more cancer deaths than occasional drinkers, a finding accentuated among low-income seniors and those with existing health problems.

“Fifty-one percent of people — or more than half — do not know that alcohol increases your risk of cancer,” said Jane Figueiredo, an epidemiologist at the Samuel Oschin Comprehensive Cancer Institute at Cedars-Sinai Medical Center in Los Angeles who served on the steering committee that prepared the report. “That’s concerning.”

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“We can talk about the myth that red wine has potential cardiovascular benefits, but there are many ways to keep your heart healthy, and these potential benefits don’t really outweigh your cancer risks,” she said.

Excessive alcohol consumption increases the risk for six types of malignancies, including esophageal squamous cell carcinoma and certain types of head, neck, breast, colorectal, liver and stomach cancers, the report found.

Some 5.4 percent of cancers in the United States — just over one in 20 cancer diagnoses — were attributed to alcohol consumption in 2019, the most recent year for which data is available.

Yet public awareness is low. One study found that fewer than one-third of women age 18 to 25 knew that alcohol use increases the risk of breast cancer.

Among adults in their 30s, cancer rates rose significantly between 2010 and 2019. The greatest increases in 2019 were in cancers of the breast, thyroid, colon and rectum, the report said.

Early-onset colorectal cancer (defined as malignancies in adults under 50) rose by 1.9 percent each year between 2011 and 2019, the report said, citing numerous published studies that have documented the trend.

Fortunately, new treatments are extending survival time for people with cancer. Death rates for women over 50 with breast cancer have fallen, as have death rates for older adults with colorectal cancer.

Yet rates of these cancers in young adults are going up, as have rates of gastric cancers and certain blood cancers, the report said. And even as patients with leukemia, melanoma and kidney cancer are living longer, the overall incidence of these diseases has been rising.

The factors driving the increase in early-onset colorectal cancer are not well understood, but many studies have shown that frequent and regular drinking in early and mid-adulthood is associated with a higher risk of colon and rectal cancers in later life.

Increased alcohol intake in mid- to late adulthood also worsens the risk. Alcohol has adverse effects on the microbiome, the collection of bacteria, fungi and viruses that live on and inside our bodies, Dr. Figueiredo said.

Drinking alters gut bacteria, which can play a role in the growth and spread of cancers.

It is also believed to increase the risk of breast cancer in women because it can raise levels of the hormone estrogen, which can fuel development of the disease. As a result, reducing alcohol consumption is one of the few ways that women can modify their risk for this disease.

And while women have long been discouraged from drinking during pregnancy for many reasons, the American Association for Cancer Research’s report provides another one: studies have shown that consuming alcohol during pregnancy increases the risk of childhood leukemia in offspring. Both moderate and high levels of drinking during pregnancy increased the risk, research has found.

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