减肥手术后结直肠癌风险增高

一项纳入77,000多例肥胖患者的回顾性队列研究显示，接受减肥手术的患者发生结直肠癌的风险显著增高。这项研究在线发表在《外科学年鉴》杂志上(2013 [doi:10.1097/SLA.0b013e318288463a])。

与美国和其他国家相同，瑞典的肥胖症患者也在增加，减肥手术数量也相应增加。在过去20年间，瑞典肥胖症的患病率已增加1倍，每年进行的减肥手术例数也由2006年的1,500例增加至2009年的4,000例。

既往一项研究得出了出乎意料的结果——肥胖手术后结直肠癌风险明显增高，而其他与肥胖相关的癌症的风险并未增高。为了验证这一点，斯德哥尔摩市卡罗林斯卡医学院的Maryam Derogar医生及其合作者使用1980~2009年间的瑞典全国注册数据，进行了这项回顾性队列研究，其中15,095例肥胖患者接受了减肥手术，62,016例患者被诊断为肥胖症但未接受手术。他们使用标准发生率比值(SIR)——观察到的病例数除以群体预期的病例数，计算结直肠癌风险。

结果显示，结直肠癌风险增高与所有3种减肥手术(垂直束带式胃成形术、可调节性束胃带捆扎术和Roux-en-Y胃旁路手术)均相关，并且随时间推移风险不断增高。在中位数为10年的随访过程中，减肥手术组发生70例结直肠癌；在中位数为7年的随访中，未接受手术组发生373例结直肠癌。减肥手术组的结直肠癌SIR为1.60，具有统计学意义。未接受手术组的风险有小幅、无统计学意义的增高(SIR为1.26)。减肥手术组男性和女性患者的风险均随时间推移而增高，在随访至少10年的患者中，风险最高增加2倍，而在未接受手术的肥胖患者中未见这一现象。

该研究由瑞典科研委员会资助。作者披露称无相关利益冲突。

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By: ELIZABETH MECHCATIE, Internal Medicine News Digital Network

The risk of colorectal cancer was significantly increased among people who had undergone obesity surgery in a retrospective cohort study of more than 77,000 obese patients enrolled in a Swedish registry.

The increased risk for colorectal cancer was associated with all three bariatric procedures – vertical banded gastroplasty, adjustable gastric banding, and Roux-en-Y gastric bypass – and increased further over time, reported Dr. Maryam Derogar, of the Karolinska Institutet, Stockholm, and her associates. No such pattern over time was seen among the obese patients who did not have surgery.

"Our data suggest that increased colorectal cancer risk may be a long-term consequence of such surgery," they concluded. If the association is confirmed, they added, "it should stimulate research addressing colonoscopic evaluation of the incidence of colorectal adenomatous polyps after obesity surgery with a view to defining an optimum colonoscopy surveillance strategy for the increasing number of patients who undergo obesity surgery. The study was published online in the Annals of Surgery (2013 [doi:10.1097/SLA.0b013e318288463a]).

To address their "unexpected" finding in an earlier study of an apparent increase in the risk of colorectal cancer after obesity surgery, but no increase in the risk of other cancers related to obesity, they conducted a retrospective cohort study using national registry data between 1980 and 2009, of 15,095 obese patients who had undergone obesity surgery and 62,016 patients who had been diagnosed with obesity but did not undergo surgery. They calculated the colorectal cancer risk using the standardized incidence ratio (SIR), the observed number of cases divided by the number of expected cases in that group.

Over a median of 10 years, there were 70 colorectal cancers in the obesity surgery group; and over a median of 7 years, 373 among those who had no surgery. The SIR for colorectal cancer among those who had surgery was 1.60, which was statistically significant. Among those who had no surgery, there was a small, insignificant increase in risk group (a SIR of 1.26). In the surgery group, the risk increased over time in men and women, up to a twofold increased risk among those patients followed for at least 10 years, a pattern than was not observed in the obese patients who had no surgery.

The "substantial increase in colorectal cancer risk, above that associated with excess body weight alone, more than 10 years after surgery is compatible with the long natural history of colorectal carcinogenesis from normal mucosa to a malignant colorectal cancer," the authors wrote. Why the risk was increased is not clear, but one possible explanation could be that the malabsorption effects of the gastric bypass procedure results in local mucosal changes, the authors speculated. Previously, they had identified rectal mucosal hyperproliferation in patients who had undergone obesity surgery, present at least 3 years after the procedure, a finding that was "associated with increased mucosal expression of the protumorigenic cytokine macrophage migration inhibitory factor," they wrote.

The study’s strengths included the size of the sample, long follow-up, and the validity of Swedish national registry data, while the limitations included the retrospective design and the lack of data on body weight over time.

As in the United States and other countries, obesity has been increasing in Sweden, with a corresponding increase in bariatric surgery. Over the last 20 years, the prevalence of obesity in Sweden has doubled, and the annual number of obesity operations performed has increased from 1,500 in 2006 to almost 4,000 in 2009, according to the authors.

The study was supported by the Swedish Research Council. The authors had no conflicts of interest to declare.