JMIR Publications

ABSTRACT

Background:

Skeletal muscle and body mass index (BMI) are essential prognostic factors for survival in colorectal cancer (CRC). However, there is a lack of understanding due to scarce studies on the continuous aspects of these variables.

Objective:

This study aimed to evaluate the prognostic impact of initial status and trajectories of muscle and BMI on overall survival (OS) and assess whether these four profiles within one year can represent the profiles 6 years later.

Methods:

We analyzed 4,056 newly diagnosed CRC patients between 2010 to 2020. The volume of the muscle with 5 mm thickness at the third lumbar spine level was measured using a pre-trained deep learning algorithm. The skeletal muscle volume index (SMVI) was defined as the muscle volume divided by the square of height. The correlation between BMI status at the first, third, and sixth years of diagnosis was analyzed and assessed similarly for muscle profiles. Prognostic significances of baseline BMI and SMVI, and their 1-year trajectories for OS were evaluated by restricted cubic spline analysis and survival analysis. Patients were categorized based on these four dimensions, and prognostic risks were predicted and demonstrated using heatmaps.

Results:

Trajectories of SMVI were categorized as decreased (20%), steady (50%), or increased (30%). Similarly, BMI trajectories were categorized as decreased (20%), steady (56%), or increased (24%). BMI and SMVI in the first year after diagnosis showed a statistically significant correlation with those in the third and sixth year. Restricted cubic spline analysis showed a non-linear relationship between baseline BMI and SMVI change ratio and OS; BMI, in particular, showed a U-shaped correlation. According to survival analysis, increased BMI (HR, 0.83; P=.02), high baseline SMVI (HR, 0.82; P=.04), and obesity stage 1 (HR, 0.80; P=.02) showed a favorable impact, while reduced SMVI trajectory (HR, 1.31; P=.001), decreased BMI (HR, 1.23; P=.02), and initial underweight (HR, 1.38; P=.02) or obesity stages 2–3 (HR, 1.79; P=.01) were negative prognostic factors for OS. Considered simultaneously, BMI >30 kg/m2 with low SMVI at the time of diagnosis resulted in the highest mortality risk. We observed improved survival in patients with increased muscle mass without BMI loss compared to those with steady muscle mass and BMI.

Conclusions:

Profiles within one year of both BMI and muscle were surrogate indicators predicting the later profiles. Continuous trajectories of body and muscle mass are independent prognostic factors of CRC patients. An automatic algorithm provides a unique opportunity to conduct longitudinal evaluations of body compositions. Further studies to understand the complicated natural courses of muscularity and adiposity are necessary for clinical application.