BMI is a simple and easy-to-determine index used to classify individuals as being underweight, overweight, or obese. The classification of BMI was established to evaluate health risks such as type 2 diabetes and cardiovascular disease[9,10
]. The associations between BMI, percentage of body fat, and distribution of body fat differ across populations, which has resulted in different cut-off points for classifications being used in different countries. Furthermore, the cut-off points for certain risks vary between different Asian populations[10
]. The Expert Consultation on BMI in Asian populations recommended that the current WHO BMI cut-off points be retained as the international classification[10
]. In the present study, BMI classifications were based on the definition of the DOH, Taiwan. In addition, the WHO BMI classifications were used to evaluate the long-term outcome of colon cancer survivors and to compare with the Taiwan BMI classification system. In the present study, the prevalence rates of diabetes and hypertension increased significantly with the BMI category; this finding is highly consistent with the intended meaning of the BMI classification system. However, the risks of other comorbidities such as asthma, hepatitis, peptic ulcer disease, and renal insufficiency were not correlated with the BMI category.
Obesity is a growing problem in Taiwan and is known to increase the risk of developing colon cancer[1-3
]. It has also been reported that obese patients have a higher risk of surgical complications[11-13
]. Previous studies have produced controversial results regarding the relationship between obesity and anastomotic leakage[14,15
]. Sorensen et al[14
] reported that obesity is not a risk factor for anastomotic leakage in colonic resection, while Biondo et al[15
] reported that obesity is an independent risk factor, but is only associated with emergent procedures of the left colon. Miransky et al[16
] reported that obesity and a contaminated surgical procedure independently predicted surgical-site infection in colorectal procedures. Riou et al[17
] reported that obesity was a significant independent risk factor for wound dehiscence. Obesity has also been reported to be a risk factor for the postoperative occurrence of pulmonary complications[18,19
]. The postoperative morbidity rate and anastomostic leakage rate did not differ significantly with the BMI category in our study. However, one of the limitations of this study is that we did not examine whether the occurrence rate of the other type of complications differed with the BMI category.
In the present study, the risk of postoperative mortality was highest in underweight patients. This finding is similar to that of Hickman et al[20
] Although obese patients have higher rates of comorbidities with cardiovascular disease and diabetes, the postoperative morbidity and mortality rates were comparable with the normal-weight patients. Conversely, the underweight patients had a lower rate of comorbidities but a higher rate of postoperative mortality than did the other patients. However, a higher proportion of underweight patients in this study were hypoalbuminemic and anemic. The observed higher postoperative mortality rate may be at least partially attributed to the associated disease conditions.
Whether obese colon cancer patients have a worse long-term outcome than other patients remains a matter of controversy. Sinicrope et al[7
] reported that underweight patients had a significantly worse OS (P
= 0.0258), and that BMI ≥ 35 kg/m2
patients exhibited a trend toward a worse DFS (P
= 0.0725) and OS (P
= 0.0805) compared with normal-weight patients, but there was no significant difference. When they analyzed the data according to patient gender, males with BMI ≥ 35 kg/m2
exhibited a reduced OS, and females with obesity (BMI = 30-34 kg/m2
) had a reduced OS when compared with their normal-weight counterparts. BMI category was significantly associated with both DFS and OS in multivariate analysis in their study. Meyerhardt et al[6
] reported that neither BMI nor weight change was significantly associated with colon cancer patient survival indicators, including the OS, DFS, and recurrence-free survival, even for underweight patients. Dignam et al[5
] reported that OS and DFS were significantly worse for underweight patients (BMI < 18.5 kg/m2
) and very obese patients (BMI ≥ 35 kg/m2
) than for normal-weight patients. Very obese patients had a greater risk of cancer recurrence or secondary primary tumors. In the present study, we found that BMI by itself was not a significant factor of CSS in colon cancer, but OS and DFS did tend to be worse for underweight patients than for the other patients. We found no differential effect of gender on either BMI or obesity. Compared with other patients, underweight patients had a worse OS but a similar CSS. This implies that many underweight patients died from noncancer events. It would have been reasonable to conclude that underlying comorbidities caused the higher mortality risk among the underweight patients, but in the present study this group actually had the smallest number of comorbidities. Further research should be conducted to establish the mechanisms responsible for the observed higher mortality risk in underweight patients. Furthermore, previous studies have shown that highly obese patients (BMI ≥ 35 kg/m2
) or males may have a worse long-term outcome than normal-weight patients, but the obese cohort of the present study was not large enough to allow analysis of the difference.
In this study, tumor location was found to be correlated with BMI, such that the proportion of patients with right colon cancer increased as the BMI category decreased. Whether patients with a lower BMI tend to have right-side colon cancer is not well known or studied. However, since the lumen is larger for the right than the left colon, symptoms related to the tumor such as small-caliber or bloody stool need more time to be sensed by patients with right colon cancer, resulting in a longer period of nutrition depletion and body weight loss. Minoo et al[21
] reported that proximally located tumors are significantly larger than those found in the distal colon. We have shown previously that the prevalence of malnutrition (hypoalbuminemia) is higher for right colon tumors than for left colon tumors[22
]. Moreover, body weight loss is more common in right colon cancer than in left colon cancer (48.8% and 33.5%, respectively; P
< 0.001). BMI is reduced in patients with body weight loss, and more patients with right colon tumors have body weight loss resulting in a lower BMI, which may partly explain the greater number of left-side tumors in the groups with a higher BMI.
The findings of this study suggest that a low BMI is a marker of weight loss, blood loss, nutrition depletion, and more-advanced disease, all of which are associated with a worse DFS and OS[22-24
]. This could be the reason why the low-BMI group had a lower DFS and OS.
This study was subject to some limitations. It lacked data regarding changes in body weight before and after surgery, measurement of central obesity, physical activity, and diet changes after surgery, and involved a smaller sample than did previous studies. However, the study’s cohort came from a single medical institution with a standard collection of patients’ data, and so there was no selection bias as might be expected in a clinical trial. The results of this study pertain to patients from Taiwan and hence may not be generalizable to other populations.
For the population of Taiwan, which represents both Chinese people and Asians in general, BMI does not appear to be a significant factor of colon-CSS, but underweight patients appear to have a higher postoperative mortality and worse OS, and are less likely to experience DFS than those in the other BMI categories. The obese patients had a higher wound complication rate, but exhibited a similar survival rate when compared to the normal-weight patients.