The leading cause of cancer depends on how you define “leading.” If you mean the factor most strongly linked to cancer risk overall, tobacco use is the single best-established preventable cause across many cancer types. If you mean which cancer causes the most deaths, lung cancer is typically responsible for the most cancer deaths worldwide. Key points to know:
- Tobacco use: The strongest, most consistently linked preventable risk factor for cancer. It increases the risk of lung cancer and many other cancers (mouth, throat, esophagus, bladder, pancreas, etc.). Reducing or quitting tobacco substantially lowers cancer risk over time.
- Global burden: Tobacco, alcohol, obesity, and air pollution are major environmental drivers of cancer incidence and mortality, with projections showing rising cancer burdens in many regions if risk factors persist.
- Specific leading sites and deaths (US context): In 2025, the cancers with the most new cases include breast, prostate, and lung, while the cancers causing the most deaths are led by lung, followed by colorectal, pancreatic, and breast in many datasets. The exact rankings can vary by country and year, but lung cancer consistently ranks highest for mortality in many populations.
If you want, I can tailor this to a specific country or region and provide the latest year-by-year breakdown of leading cancer sites by incidence and by mortality.