Normal Curves: Sexy Science, Serious Statistics8 Sep 2025

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. 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

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