Exercise and Cancer: Does physical activity improve colon cancer survival?

Exercise has long been hailed as cancer-fighting magic, but is there hard evidence behind the hype? In this episode, we tackle the CHALLENGE trial, a large phase III study of colon cancer patients that tested whether prescribed exercise could improve cancer-free survival. We translate clinical jargon into plain English, show why ratio statistics make splashy headlines while absolute differences tell the real story, and take a detour into why statisticians think survival analysis is downright sexy. And we even bring in a classic reality show to make sense of the numbers.

Statistical topics

• Data and Safety Monitoring Board (DSMB)
• Hazard ratios
• Intention-to-treat analysis
• Interim analyses
• Kaplan-Meier curves
• Phase III trials
• Randomized clinical trial
• Rates and rate ratios
• Relative vs absolute differences
• Stratified randomization with minimization
• Survival analysis
• Time-to-event variables
Methodological morals

• “Ratio statistics sell headlines. Absolute differences sell truth.”
• “Survival analysis is this sexy stats tool that makes every moment and every Cox count.”
References
• Courneya KS, Vardy JL, O'Callaghan CJ, et al. Structured Exercise after Adjuvant Chemotherapy for Colon Cancer (nejm.org/doi/full/10.1056/NEJMoa2502760). NEJM. 2025;393:13-25.
• Rabin RC. Are Marathons and Extreme Running Linked to Colon Cancer? (nytimes.com/2025/08/19/health/running-colon-ca…) The New York Times. Aug 19, 2025.
• Sainani KL. Introduction to survival analysis (onlinelibrary.wiley.com/doi/10.1016/j.pmrj.201…). PM&R. 2016; 8:580-85.
• Sainani KL. Making sense of intention-to-treat (onlinelibrary.wiley.com/doi/10.1016/j.pmrj.201…). PM&R. 2010;2:209-13.

Thanks
Thanks to Caitlin Goodrich for the episode topic tip!

Kristin and Regina’s online courses:

Demystifying Data: A Modern Approach to Statistical Understanding (online.stanford.edu/courses/som-xche0033-demys…)
Clinical Trials: Design, Strategy, and Analysis (online.stanford.edu/courses/som-xche0030-clini…)
Medical Statistics Certificate Program (online.stanford.edu/programs/medical-statistic…)
Writing in the Sciences (coursera.org/learn/sciwrite)
Epidemiology and Clinical Research Graduate Certificate Program (online.stanford.edu/programs/epidemiology-and-…)
Programs that we teach in:
Epidemiology and Clinical Research Graduate Certificate Program (online.stanford.edu/programs/epidemiology-and-…)

Find us on:
Kristin - LinkedIn (linkedin.com/in/kristin-sainani-642b5914) &Twitter/X (x.com/KristinSainani)
Regina -LinkedIn (linkedin.com/in/reginanuzzo) &reginanuzzo.com/ReginaNuzzo.com (reginanuzzo.com)

• () - Intro

• () - Two different types of cancer studies

• () - Why might exercise affect cancer?

• () - Phase III trials are different

• () - Who was in the CHALLENGE trial?

• () - Stratified randomization with minimization

• () - The exercise prescription

• () - What did the CHALLENGE trial measure?

• () - Disease-free survival

• () - Data and Safety Monitoring Board – what do they do?

• () - Participants and adherence to exercise

• () - Intention-to-treat analysis

• () - Survival analysis overview

• () - Kaplan-Meier curves

• () - Reality-show analogy

• () - Ratio statistics are confusing

• () - Hazard ratios

• () - Wrap-up, rating, and methodological morals

Exercise and Cancer: Does physical activity improve colon cancer survival?

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