Most of us know someone whose life has been upended by a cancer diagnosis.
The question that follows is almost always the same. How much of this could have been avoided?
A new estimate puts a figure on it. The American Association for Cancer Research's Cancer Progress Report 2026 found that about 40 percent of new cancer cases diagnosed in the US in 2019 were linked to around 30 modifiable risk factors.
Modifiable means habits or exposures that can, in principle, be changed. The report groups the biggest drivers into six broad categories.
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Six main risk categories
Tobacco use is still the single leading preventable cause and is tied to just under 20 percent of all US cancer cases.
Ultraviolet radiation from sun and tanning beds accounts for about 92 percent of melanomas.
Excess body weight is linked to roughly 7.6 percent of cases and alcohol to about 5 percent.
Diet and physical inactivity sit alongside weight in the same cluster, with poor diet contributing to a meaningful share on its own.
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Infectious agents account for another 3.4 percent or so of US cases.
The main ones are HPV, hepatitis B and C, and the stomach bacterium Helicobacter pylori, each tied to specific cancers.
There is real progress in the headline numbers too. The overall US cancer death rate dropped by 35 percent between 1991 and 2024, which the report estimates prevented about 4.8 million deaths.
The adult smoking rate also slipped below 10 percent for the first time in 2024.
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The cautious new entry on GLP-1 weight-loss drugs
A fresh angle in this year's report is GLP-1 drugs, the newer class of weight-loss and diabetes medicines that includes semaglutide, the active ingredient in Novo Nordisk's Ozempic and Wegovy.
Some analyses have linked semaglutide to a 12 percent lower risk of obesity-related cancers. GLP-1 use in people with type 2 diabetes has been tied to sharply lower risks of esophageal and colorectal cancer compared with insulin.
But a review of 48 clinical trials with more than 94,000 participants found no overall reduction in obesity-related cancer risk.
Keith Flaherty is AACR president and director of clinical research at Massachusetts General Hospital Cancer Center.
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He told Targeted Oncology that researchers are still in the very early days of understanding the impact.
A short checklist you can act on today
The practical takeaway is not a single magic habit. It is a short list that lines up with the risk categories the AACR report highlights.
Do not smoke, and avoid secondhand smoke. Limit alcohol. Move more, aim for a healthy weight, and eat more vegetables, fruit and whole grains and less processed meat.
Protect your skin from the sun and skip indoor tanning. Keep up with HPV vaccination for eligible children and young adults, and with hepatitis B and C testing when it is recommended by your doctor.
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Screening still matters even for people doing everything right. The report points to colorectal, breast, cervical and lung cancer screening as proven ways to catch the disease earlier, when treatment works better.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.