Preoperative BMI Affects Long-Term Survival Outcomes After Colorectal Cancer Operation

Male Surgeon and Surgical Assistant in operating room of hospital performing Endoscopy procedure on patient, colonoscopy, crc, polyp
Researchers sought to evaluate the effect of body mass index on the survival outcomes of patients undergoing an operation for colorectal cancer.

Patients undergoing a surgical procedure for colorectal cancer (CRC), who are classified as underweight or having obesity per calculated body mass index (BMI), may experience poorer long-term survival outcomes compared with patients of normal weight, according to findings published in the European Journal of Cancer.

Researchers conducted a systematic review and meta-analysis of literature obtained from PubMed, MEDLINE, Embase, Science Citation Index Expanded, and CENTRAL in the Cochrane Library published up until March 18, 2021.  Of the3949 studies identified, 56 publications met inclusion criteria for the analysis based on risk of bias scoring.

In the meta-analysis, researchers analyzed the data from 72,582 patients (43% women) with CRC. Researchers also divided the patients into 5 groups based on BMI: BMI less than 18.5 (underweight); BMI between 18.5 to 25 (normal); BMI between 25 to 30 (overweight); BMI between 30 to 35 (obesity); and BMI greater than 35 (morbid obesity). If applicable, they also subdivided patients according to type of cancer — colon or rectal cancer only.

Patients with CRC and a BMI less than 18.5 demonstrated significantly worse overall survival (hazard ratio [HR], 1.91; 95% CI, 1.54-2.36; P <.0001), cancer-specific survival (HR, 1.91; 95% CI, 1.42-2.55; P <.0001), disease-free survival (HR, 1.50; 95% CI, 1.28-1.76; P <.0001), recurrence-free survival (HR, 1.13; 95% CI, 1.03-1.23; P <.007) compared with patients who had normal BMIs. The trend of lower BMIs resulting in worse clinical outcomes was also identified in the rectal cancer subgroup.

Patients with rectal cancer who had a BMI greater than 25 demonstrated significantly better overall survival rates than patients with BMI less than 25 (HR, 0.74; 95% CI, 0.57-0.97; P =.03). Patients with rectal cancer and a BMI less than 18.5 demonstrated decreased overall survival and disease-free survival compared with patients with rectal cancer who had normal BMIs. Moreover, patients with colon cancer who had BMIs of 25 to 30 survived longer overall (HR, 0.90; 95% CI, 0.813-1.00; P =.05) and maintained longer disease-free survival than patients with normal BMIs (HR, 0.90; 95% CI, 0.82-1.00; P =.04).

Compared with patients who had normal BMIs, patients with CRC and a BMI greater than 30 demonstrated significantly worse disease-free survival (HR, 1.05; 95% CI, 1.01-1.11; P =.03). Similarly, patients with CRC and a BMI greater than 35 exhibited worse overall survival (HR, 1.24; 95% CI, 1.04-1.48; P =.02), cancer-specific survival (HR, 1.36; 95% CI, 1.06-1.74; P =.01), and disease-free survival (HR, 1.15; 95% CI, 1.01-1.32; P =.03) compared with patients who had normal BMIs.

Patients with BMI greater than 35 in the colon or rectal cancer subgroups as well as patients with BMI over 30 in the colon cancer subgroup demonstrated worse clinical outcomes compared with patients with normal BMIs.

Study limitations included the possibility of bias; the heterogeneity of studies used; the sole use of BMI to measure obesity instead of using other potentially more reliable measurements, such as visceral fat, regional fat, muscular volume, or bioelectrical impedance; and probability of reverse causality, since BMI increases risk for cancer, but cancer also affects BMI.

“In conclusion, this review reinforces that being underweight or class II obese at the time of surgery for colorectal is detrimental to survival outcomes,” the researchers noted. “However, being overweight (BMI 25-30) may improve survival. BMI alone is inadequate to assess fat mass and distribution; hence, future studies should endeavour to utilise other anthropometric tools. The findings from these tools, along with a thorough nutritional assessment, should be considered by all multidisciplinary teams managing patients with colorectal cancer.”


Simillis C, Taylor B, Ahmad A, et al. A systematic review and meta-analysis assessing the impact of body mass index on long-term survival outcomes after surgery for colorectal cancer. Eur J Cancer. 2022;172:237-251. doi:10.1016/j.ejca.2022.05.020