PHOENIX-Being overweight or even obese doesn't increase your risks of complications following lung resection for cancer-but being underweight and being morbidly obese do add risk to the procedures, researchers reported at the Society of Thoracic Surgeons Annual Meeting.
"Increased body mass index is generally not associated with increased risk, whereas underweight patients are at substantially increased risk," said Trevor Williams, MD, who performed the research while a fellow in thoracic surgery at the University of Chicago.
At a press conference, Williams reported that the risk of any complication following lung resection surgery was 44 percent greater among patients classified as being underweight at the time of their surgery when compared with other groups of patients who were stratified on the basis of body mass index (P=0.001).
On the other hand, the researchers found that being overweight was somewhat protective, reducing risk of all complications by 21 percent compared with people of normal weight who were undergoing the surgery (P<0.001).
Studying BMI Factors
The study included all patients who underwent major lung resection-41,446 patients from 2009-2014. Cases of extended resection, such as surgery to the chest wall or resecting the main airway, were excluded from the analysis. The patients were stratified by WHO body mass index category: Patients with a body mass index of less than 18.5 kg/m2 were considered as being underweight and they represented 3 percent of the total sample; about 34 percent of the patients fell into the normal body mass index category 18.5 kg/m2 to 24.9 kg/m2; 35 percent of the group was classified as overweight with a body mass index of 25 kg/m2 to 29.9 kg/m2; obese patients represented 28 percent of the total and that group was further stratified as Obese 1 (30 kg/m2 to 34.9 kg/m2); Obese 2 (35 kg/m2 to 39.9 kg/m2) and Obese 3, a body mass index of 40 or greater.
Williams, who now practices at Mercy San Juan Medical Center, Carmichael, Calif., said that even moderately obese patients appeared to be protected from complications. Patients in the Obese 1 class had a 23 percent reduced risk of all complications (P<0.001), and people in the Obese 2 class had a 30 percent reduced risk of complications (P<0.001).
However, the "J-shaped curve" of outcomes showed that if a person was morbidly obese, in the Obese 3 category, the risk of complications was reduced just 11 percent, a result that did not reach statistical significance. When Williams and colleagues scrutinized the incidence of major complications, the risk was significantly higher in the Obese 3 class-an 18 percent increased risk (P=0.028).
The underweight population in the study was also at a significantly greater risk of pulmonary complications, Williams said. The risk of these complications was 41 percent greater for the people who were underweight (P=0.001). Being overweight or in the Obese 1 and Obese 2 categories apparently reduced the risk of complications, but patients in the Obese 3 group had a 12 percent higher risk, although that was not significant (P=0.186).
Effect of Weight on Outcomes
In commenting on the study, press conference moderator Robbin Cohen, MD, Associate Professor of Cardiothoracic Surgery at the University of South California Keck School of Medicine, Los Angeles, told Oncology Times, "I think the reason that underweight people fared poorly in this study has to be lower body mass index is a marker of frailty.
"The fact is, the fit patients do fine after these procedures," he said. "The ones who are underweight are really, in my mind, the ones who are sick. But it probably is not a good thing to be overweight either."
By percentage, more women were underweight, normal weight, and obese than men; men were slightly more overweight than women. Increasing body mass index was associated with increasing comorbidities, notably coronary artery disease, diabetes, and hypertension. The prevalence of chronic obstructive pulmonary disease was more common among underweight persons, and seemed to decrease with increasing body mass index. Smoking status was most prevalent in the underweight population. The patients underwent open surgery about as often as minimally invasive surgical techniques were employed, the researchers reported.
"The prevalence of obesity in the United States has been increasing for decades with more than 70 percent of the people being characterizes as overweight or obese," Williams said, in discussing the rationale for undergoing the study. "The number of medical morbidities increases with increasing body mass index. This may affect surgical outcomes. The medical literature states that increasing obesity is associated with increasing case complexity as well as increasing the time of the operation.
"Reports analyzing outcomes among obese patients are not consistent and this may have a lot to do with stratifying outcomes based on 'high' or 'low' body mass index and not taking a more granular look at different categories. More importantly, the effect of being underweight has rarely been studied specifically. A study from out institution recently identified that being underweight as an important independent risk factor for pulmonary complications after lung resection surgery.
"It is likely that a complex relationship exists between body mass index and outcomes after lung resection," Williams concluded.
Ed Susman is a contributing writer.