Hierarchy of evidence in medical science – aspirin for colorectal cancer prevention case

Activities

June 11, 2025

Hierarchy of evidence in medical science – aspirin for colorectal cancer prevention case

Pre-requisites

Basic Understanding of Study Designs, Introduction to Evidence-Based Medicine (EBM), Basic Clinical Knowledge of Colorectal Cancer (CRC), Basic Pharmacology of Aspirin

Explanation of activity

Students are divided into small groups. Each group is assigned one study from a different level in the hierarchy. Their task is to review the study and present: type of study and where it fits in the hierarchy, main finding, strengths and limitations and applicability to the clinical case.

Clinical Scenario Introduction

A 55-year-old man with a family history of colorectal cancer asks whether he should start taking low-dose aspirin to reduce his risk of developing cancer. He has no history of cardiovascular disease, gastric ulcers, or bleeding disorders.

Prompt to students: How would you approach this question using evidence-based medicine?

Discussion Questions

Which study provides the highest level of evidence?
What are the limitations of applying population-level data to an individual?
How do the risks (e.g., bleeding) factor into your recommendation?
How would you communicate this evidence to the patient?

Wrap-up: Summary and Clinical Application

Recap the hierarchy of evidence and how it influenced your clinical decision.
Discuss ongoing research needs in the field of chemoprevention.

Teacher materials

Further reading to further develop the activity/understanding of the topic:

Gordis Epidemiology By David D Celentano, Moyses Szklo · 2018 ISBN:9780323552318, 0323552315, October 19, 2018, Elsevier

Student Materials

Rohwer N, Kühl AA, Ostermann AI, et al. Effects of chronic low-dose aspirin treatment on tumor prevention in three mouse models of intestinal tumorigenesis. Cancer Med. 2020; 9: 2535–2550. https://doi.org/10.1002/cam4.2881
Colonic carcinoma unmasked by dual antiplatelet therapy
Wysota, B.A. et al. European Journal of Internal Medicine, Volume 19, Issue 7, 558, DOI: 10.1016/j.ejim.2008.01.008
Low-Dose Aspirin or Nonsteroidal Anti-inflammatory Drug Use and Colorectal Cancer Risk: A Population-Based, Case–Control Study
Authors: Søren Friis, MD, Anders H. Riis, MSc, Rune Erichsen, MD, John A. Baron, MD, and Henrik T. Sørensen, MD, DMSc Author, Article, & Disclosure Information
Publication: Annals of Internal Medicine
Volume 163, Number 5
https://doi.org/10.7326/M15-0039
Long-term effect of aspirin on cancer risk in carriers of hereditary colorectal cancer: an analysis from the CAPP2 randomised controlled trial
Burn, John et al.
The Lancet, Volume 378, Issue 9809, 2081 – 2087 DOI: 10.1016/S0140-6736(11)61049-0
Aspirin and the risk of colorectal and other digestive tract cancers: an updated meta-analysis through 2019
Bosetti, C. et al. Annals of Oncology, Volume 31, Issue 5, 558 – 568, DOI: 10.1016/j.annonc.2020.02.012

Assessing and Evaluation

Learning Objectives

By the end of this session, students should be able to:

Understand the concept of the hierarchy of evidence in clinical research.
Critically appraise different types of studies (RCTs, cohort studies, meta-analyses).
Analyze the current evidence regarding aspirin use for colorectal cancer (CRC) prevention.
Discuss the balance of benefits and risks in chemoprevention strategies.

Short quiz or reflective writing: Rank the provided studies by evidence level and justify. Write a 100-word recommendation note to the patient.

Modulations

Different example: psilocybin for depression treatment:

Response of cluster headache to psilocybin and LSD R Andrew Sewell 1, John H Halpern, Harrison G Pope Jr, PMID: 16801660 DOI: 10.1212/01.wnl.0000219761.05466.43
Why psychiatry needs psychedelics and psychedelics need psychiatry Ben Sessa PMID: 24830186 DOI: 10.1080/02791072.2014.877322
Trial of Psilocybin versus Escitalopram for Depression Authors: Robin Carhart-Harris, Ph.D., Bruna Giribaldi, B.Sc., Rosalind Watts, D.Clin.Psy., Michelle Baker-Jones, B.A., Ashleigh Murphy-Beiner, M.Sc., Roberta Murphy, M.D., Jonny Martell, M.D., Allan Blemings, M.Sc., David Erritzoe, M.D., and David J. Nutt, M.D. Published April 14, 2021, N Engl J Med 2021;384:1402-1411, DOI: 10.1056/NEJMoa2032994, VOL. 384 NO. 15
Efficacy of psilocybin for treating symptoms of depression: systematic review and meta-analysis Athina-Marina Metaxa 1, Mike Clarke, PMID: 38692686 PMCID: PMC11062320 DOI: 10.1136/bmj-2023-078084
Effects of psilocybin on hippocampal neurogenesis and extinction of trace fear conditioning Briony J Catlow 1, Shijie Song, Daniel A Paredes, Cheryl L Kirstein, Juan Sanchez-Ramos PMID: 23727882 DOI: 10.1007/s00221-013-3579-0
Naturalistic psilocybin use is associated with persisting improvements in mental health and wellbeing: results from a prospective, longitudinal survey Sandeep M Nayak 1 2, Hillary Jackson 1 2, Nathan D Sepeda 1 2 3, David S Mathai 1 2, Sara So 1 2, Abigail Yaffe 1 2, Hadi Zaki 1 2, Trey J Brasher 4, Matthew X Lowe 4, Del R P Jolly 4, Frederick S Barrett 1 2 5 6, Roland R Griffiths 1 2 6, Justin C Strickland 1 2, Matthew W Johnson 1, Heather Jackson 4, Albert Garcia-Romeu 1 2 PMID: 37795509 PMCID: PMC10545967 DOI: 10.3389/fpsyt.2023.1199642