Summary of "We Were Wrong About Aspirin (New Evidence)"

Scientific Concepts, Discoveries, and Nature/Medical Phenomena

Primary prevention: Taking aspirin in people without prior cardiovascular events to prevent future disease. (This is the video’s focus for cancer outcomes.)
Secondary prevention: Taking aspirin after cardiovascular events (e.g., heart attack, stroke, stent).
- Stopping can be dangerous, and this is treated as a different evidence base.

A case-control study reported that people with colorectal cancer used less aspirin than controls.
After adjustments, aspirin use showed a protective association across colon/rectal cancer and across sexes.

Confounding/selection may explain associations:
- People who take aspirin may differ systematically from those who don’t.
Therefore, causality is unclear.

Peter Rothwell (Oxford) combined cancer outcomes hidden within large heart/stroke trials:
- Found about a 21% reduction in cancer deaths overall.
- Benefits appeared to increase with longer follow-up.
- Gastrointestinal cancer deaths showed the clearest signal, reported as >50% reduction after extended time (e.g., ~7.5+ years).

2016 USPSTF recommendation:
- Recommended daily low-dose aspirin (age-based), including reasoning tied to colorectal cancer prevention.
Later evidence undermined the “cancer shield” narrative.

Randomized aspirin vs placebo in healthy older adults:
- Age: ≥70, or ≥65 for Black/Hispanic participants.
Exclusions included:
- dementia, disability, and baseline cardiovascular disease.

Aspirin did not prevent first heart attack or stroke.
Cancer results diverged from Rothwell’s prediction:
- People on aspirin died more often from cancer.

Cancer incidence: reported as identical between aspirin and placebo.
Colorectal cancer incidence: also identical, with hazard ratio ~1.01.
Cancer deaths: about 15% higher in the aspirin group.
After stopping aspirin (over ~4.5 years):
- The increased cancer mortality signal vanished.
- Interpretation: harm may be linked to active use.

Pooled 10 randomized trials with >124,000 participants.
In the 5–10 year window relevant to starting aspirin in older adulthood:
- Colorectal cancer mortality was reported as ~77% higher with aspirin.
Certainty was rated low.
- Possible benefit at ≥15 years was noted, but with very low certainty.

Cancer metastasis can involve platelets escorting circulating tumor cells.
Platelets release thromboxane A2, which suppresses T cells (immune cells that kill rogue cancer cells).
Aspirin’s low-dose effect:
- reduces platelet production of thromboxane A2.
Mouse/young-immune-system experiments suggested aspirin could reduce metastasis by “releasing the brakes” on T cells, potentially reducing metastatic deaths.

Immunosenescence: Aging may make T cells less responsive; removing thromboxane-related braking may not help.
Masking early symptoms: Anti-inflammatory effects might delay cancer detection by dampening early inflammatory symptoms.
Chronic immune/inflammatory suppression harms tumor surveillance:
- Inflammation is part of how the body identifies and controls dangerous cells.
- Long-term suppression could allow established tumors to grow.

CaPP2 (10-year follow-up; The Lancet, 2020):
- Population: Lynch syndrome carriers (genetic risk up to ~60% lifetime colorectal cancer risk).
- Intervention: 600 mg/day aspirin (higher than typical 100 mg “low-dose”); median age ~45.
- Result: about a 35% reduction in colorectal cancer.
Video-implied conclusion:
- Any cancer prevention effect may depend on:
  - the person (genetic susceptibility),
  - the dose,
  - starting age / immune context, and
  - duration.

Aspirin is associated with about a 59% increased risk of serious bleeding (outside the brain; e.g., GI bleeding).
This bleeding risk was described as high-certainty in a Cochrane review.

Meta-analysis of randomized controlled trials (Rothwell)
- Extracted cancer endpoints from older cardiovascular RCTs.
- Analyzed 8 RCTs with >25,000 patients.
- Evaluated cancer death reduction over time on aspirin and with longer follow-up.
ASPREE (Aspirin in Reducing Events in the Elderly)
- Randomized, placebo-controlled trial.
- Population: healthy older adults (≥70; or ≥65 for Black/Hispanic).
- Exclusions: cardiovascular disease, dementia, disabilities.
- Intervention: 100 mg daily aspirin vs placebo.
- Outcomes: cardiovascular events and cancer incidence/mortality (with extended follow-up).
Cochrane Systematic Review
- Updated synthesis of 10 RCTs (>124,000 participants).
- Assessed mortality/incidence outcomes in relevant follow-up windows (5–10 years and ≥15 years).
CaPP2 (Lynch syndrome prevention trial)
- Randomized trial in Lynch syndrome carriers.
- Intervention: 600 mg/day aspirin vs comparison (per CaPP2 protocol).
- Follow-up: 10 years, reporting colorectal cancer reduction.

Peter Rothwell (Oxford neurologist)
John McNeil (Professor of epidemiology, Monash University) — led ASPREE
Gabriel Kune (Melbourne surgeon; 1988 case-control study)
Susan Orchard (Monash; director of ASPREE extension; lead author of the JAMA Oncology follow-up described)
Cochrane Library / Cochrane authors (systematic review)
US Preventive Services Task Force (USPSTF)
Cambridge researchers (mechanism work on thromboxane A2 and T-cell suppression; not individually named in the subtitles)
ASPREE team (group-level mention; individual members not fully listed)
CaPP2 researchers (individual authors not named in the subtitles)