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

Normal Curves: Sexy Science, Serious Statistics

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. 2025;393:13-25.
• Rabin RC. Are Marathons and Extreme Running Linked to Colon Cancer? The New York Times. Aug 19, 2025.
• Sainani KL. Introduction to survival analysis. PM&R. 2016; 8:580-85.
• Sainani KL. Making sense of intention-to-treat. 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

Clinical Trials: Design, Strategy, and Analysis

Medical Statistics Certificate Program

Writing in the Sciences

Epidemiology and Clinical Research Graduate Certificate Program

Programs that we teach in:

Epidemiology and Clinical Research Graduate Certificate Program

Find us on:

Kristin - LinkedIn & Twitter/X

Regina - LinkedIn & ReginaNuzzo.com

• (00:00) - Intro
• (05:42) - Two different types of cancer studies
• (08:12) - Why might exercise affect cancer?
• (10:05) - Phase III trials are different
• (12:40) - Who was in the CHALLENGE trial?
• (13:31) - Stratified randomization with minimization
• (15:05) - The exercise prescription
• (18:23) - What did the CHALLENGE trial measure?
• (19:10) - Disease-free survival
• (21:05) - Data and Safety Monitoring Board – what do they do?
• (23:41) - Participants and adherence to exercise
• (26:00) - Intention-to-treat analysis
• (29:04) - Survival analysis overview
• (30:57) - Kaplan-Meier curves
• (33:33) - Reality-show analogy
• (36:00) - Ratio statistics are confusing
• (38:36) - Hazard ratios
• (46:09) - Wrap-up, rating, and methodological morals