The EORTC QLQ-C30 questionnaire was used to investigate HRQoL in patients with colon cancer in this population-based study. The univariate analysis showed that patients with colon cancer had a worse HRQoL compared with a Swedish reference population both at baseline and at the six-month follow-up as indicated by changed scores for 3/5 functional (role, emotional and social), and 4/9 symptom scales (fatigue, nausea/vomiting, appetite loss and diarrhoea). Furthermore, the major findings of this study, identified using linear regression analyses, were that patients whose planned surgery included a stoma (with or without resection), patients with more co-morbidities (ASA III and IV) and smokers were at higher risk of a lower HRQoL than the other included patients.
It is difficult to compare our findings with those of other studies that used a reference population because these vary in methodology and the reference values used . However, consistent with our results, a study  of Finnish patients with colorectal cancer compared their data with reference data using the EORTC QLQ-C30 questionnaire, and found that pain, fatigue and financial difficulties were the main drivers of poor health. Another study conducted in Germany by Jansen et al.  also compared colorectal cancer patients with controls from the general population, and showed that diarrhoea and financial difficulties were worse in patients with colorectal cancer.
Several countries have assessed HRQoL in colon cancer patients, but only one randomized study comparing the effects of open and laparoscopic surgery in Sweden has been published . Apart from that study, there is no published information regarding HRQoL in Swedish colon cancer patients.
Contradicting results have been presented regarding whether the presence of a stoma in surgically treated colorectal cancer patients has a negative effect on HRQoL. Most of these studies have been performed on patients with rectal cancer [23,24]. Of note, the patients in our study completed the questionnaire before they underwent surgery to create a stoma. This implies that it was the patients’ risk factors (as judged by the surgeon) or the advanced stage of their cancers that were related to the observed lower HRQoL in these patients. They might also have had poor expectations of life with a stoma, or it may have been that it was the information that they were to receive a stoma per se that contributed to their poor scores. Although this study included very few patients who were treated with a stoma alone, this group showed significantly worse functional scores and increased symptom scores compared with patients treated with a stoma plus colon resection. However, a recent study of colon cancer patients who answered questions postoperatively reported that 78% considered not having a permanent stoma as the most important factor analysed (76% stated that “being cured” was most important) .
This study found that HRQoL was not affected by whether the patients underwent right-sided, left-sided or total colectomy (data not shown), and that patients with an advanced tumour stage (TNM IV) did not have significantly worse HRQoL than other patients. However, 10 of the 14 patients who were treated with a stoma without resection had metastatic disease (TNM IV), and these patients had very low functional scores and high symptom scores, indicating worse HRQoL at both baseline and at the six-month follow-up.
Our study also found that younger patients had worse emotional and social functional QoL and more bowel problems (nausea/vomiting and diarrhoea) than older patients. This has also been observed by others and suggests that data presented for HRQoL should use age-matched groups [26,27].
In our study, co-morbidity as assessed by ASA grade had a negative impact on global QoL, physical function, fatigue, dyspnoea and constipation, both at baseline and at the six-month follow-up. These data are also consistent with the results of other studies of colorectal cancer and other cancer types such as head and neck, lung, and prostate cancer . In breast cancer, the effect of co-morbidity explained most of the variance in nearly all subscales comparing demographic and clinical variables .
Our data also showed that patients with a higher BMI had worse physical function and more nausea and vomiting, pain and financial difficulties. This observation has also been reported by others . Considering several different lifestyle factors, Schlesiger et al.  found that being non-obese had the strongest association with a high HRQoL, while another study reported decreased HRQoL in Dutch patients with high BMI .
The present study also showed that smokers had worse QoL than other patients at the six-month follow-up compared with baseline. These data are consistent with the findings of studies of the general population  and of colorectal cancer patients . It has also been reported that survivors of colon cancer and melanoma had higher age-adjusted smoking rates than survivors of other cancers .
The main strengths of this study were its prospective design and that it was population based. The patient data were compared with those from a Swedish reference population . We also used one of the most widely used cancer-specific validated analysis instruments and analysed the data from non-included patients. In addition, we performed multiple regression analyses of medically important parameters, including lifestyle factors, such as BMI and smoking.
Analysis of data from the non-included patients showed that these had higher co-morbidity, were less often treated surgically, had more advanced-stage tumours and where surgical treatment more often included stoma creation. Thus, presumably if these patients had been included, our results would have shown a worse outcome for HRQoL because these non-included patients had risk factors for lower HRQoL . However, a possible limitation is that some patients were too ill to complete the questionnaire, implying a possible selection bias.
Other limitations were that this was a single-centre study, the reference data for the Swedish general population were from 2000  and we did not measure social and psychological factors known to influence HRQoL . A small study by Siassi et al.  showed that personality affects HRQoL more than clinical variables after major surgery. A study of Turkish colorectal cancer patients demonstrated a clear association between anxiety/depression symptoms and HRQoL . We did not include data on the effect of chemotherapy, but others have shown that it is a major factor affecting HRQoL [12,15].