Does weight influence survival in patients with colorectal cancer?

This review evaluated the association between body mass index (BMI) and survival in patients with colorectal cancer (CRC). 

The Body Mass Index (BMI) is a simple index relating weight to height used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided to the square of height in meters. A BMI under 18.5 kg/m² is considered underweight, over 25 kg/m² is considered overweight and over 30 kg/m² obesity. Currently, a third of the adults in the United States are considered overweight or obese. Obesity is known to be a risk factor for many conditions, including CRC. However, it is not clear if obesity has any effects on survival in patients with CRC. The current study examined whether there was an association between high BMI and CRC survival. 

This analysis reviewed 21 studies that included overall 25291 CRC patients. All patients had undergone surgery to remove the cancer. BMIs had been recorded at the start of the clinical trials: 36% and 17.6% of the patients followed were considered overweight and obese, respectively, and 7.3% were considered underweight. After approximately 7.8 years of follow up, the authors of the study found that obese patients were more likely to have cancer spread to the lymph nodes compared to normal-weight patients. Also, compared to normal-weight patients, obese patients had shorter time until the cancer returned (recurrence) and shorter survival. Underweight patients were also found to have shorter survival and time until recurrence. This effect was more commonly observed in obese or underweight men than in obese or underweight women. 

In summary, BMI was shown to negatively affect the outcomes for both obese and underweight patients diagnosed with CRC.

This study looked back at patients who have been treated in the past (retrospective study) rather than following the patients throughout their treatment and determining their outcomes (prospective study). Retrospective studies are considered to provide weak statistical evidence.