Part 16
Cancer: Prevention and Early Detection
ILLUSTRATION. Two neighbors discuss cancer screening. One has bought a multi-cancer blood test but keeps postponing her recommended colorectal screening. The other has completed standard screening and wonders whether to add anything. They are considering the same product from different starting points. The first decision is what established care is still missing.
Clinical scenes in this edition are explicitly labeled illustrations. They describe imagined situations used to explain medical decisions, not documented patients, diagnoses, conversations, or treatment outcomes. They should not be read as evidence that a particular intervention works. Personal recollections are recollections, not medical records.
Evidence grade (draft mapping). 16 questions; a question with mixed evidence counts under each grade.
- 220. How much cancer is preventable?About 40 percent of cancers and nearly half of cancer deaths in the United States are tied to risk factors we can change.CObservational
- 221. What are the biggest levers for prevention?Tobacco, body weight, alcohol, sunlight, physical activity, certain infections, and diet, roughly in that order.ARobust human trials
- 222. Is it true that some cancers are caused by infections?Yes. Roughly one in eight cancers worldwide is caused by an infection that can be prevented or treated.ARobust human trials
- 223. Can exercise really affect cancer?Yes. Active people get fewer cancers, and in 2025 a randomized trial showed that exercise after colon cancer treatment improved survival.Grade pending
- 224. Which cancer screenings are proven to save lives?Established screening includes colorectal, breast, cervical, and eligible high-risk lung screening. The right test, interval, and stopping age depend on the guideline and your circumstances.ARobust human trials
- 225. Colonoscopy, stool test, or blood test: which is best for colon cancer?Colonoscopy is the most thorough because it finds and removes polyps before they become cancer. The best test, though, is the one you will actually do.GGuideline-based / consensus
- 226. What should women know about breast screening beyond the mammogram?Know your breast density and your personal risk. Both change what screening you need.GGuideline-based / consensus
- 227. What is the Galleri test, and how does it work?It is a blood test that looks for fragments of DNA shed by tumors and can signal more than fifty types of cancer, most of which have no screening test at all.Grade pending
- 228. What have the Galleri trials actually shown?A low false-alarm rate, good accuracy when it is positive, and modest sensitivity. It finds roughly one cancer in three overall and misses most of the earliest ones. Its largest trial did not meet its main goal.Grade pending
- 229. Is Galleri approved, and what does it cost?As of October 2026 it is not FDA approved, though a decision is expected soon. It costs about $950 and is rarely covered by insurance.RRegulatory status
- 230. Should I take the Galleri test?This is a preference-sensitive choice with uncertain net benefit, not a standard layer that everyone over 50 needs.JClinical judgment / author synthesis
- 231. Should I get a full-body MRI to look for cancer?For most healthy people, no, for the reasons explained in Part 4: it finds many harmless things and has not been shown to save lives.FNot demonstrated / insufficient
- 232. What is overdiagnosis?Finding a “cancer” that would never have caused harm in your lifetime, and treating it anyway.ARobust human trials
- 233. Do aspirin, vitamin D, or supplements prevent cancer?No supplement is established as broad cancer prevention for the general population, and some high-dose products raise risk. Specific clinical indications need separate evaluation. Aspirin is no longer recommended for cancer prevention in the general population.ARobust human trials
- 234. When should I have genetic testing for cancer risk?When cancer appears in your family at young ages, in several relatives, or in certain patterns.GGuideline-based / consensus
- 235. What about ivermectin, fenbendazole, and other “hidden” cancer cures?There is no good human evidence that they treat cancer, and the stories about suppressed cures do not hold up.FNot demonstrated / insufficient