Anaesthetic techniques for risk of malignant tumour recurrence.

BACKGROUND
Surgery remains a mainstay of treatment for malignant tumours; however, surgical manipulation leads to a significant systemic release of tumour cells. Whether these cells lead to metastases is largely dependent on the balance between aggressiveness of the tumour cells and resilience of the body. Surgical stress per se, anaesthetic agents and administration of opioid analgesics perioperatively can compromise immune function and might shift the balance towards progression of minimal residual disease. Regional anaesthesia techniques provide perioperative pain relief; they therefore reduce the quantity of systemic opioids and of anaesthetic agents used. Additionally, regional anaesthesia techniques are known to prevent or attenuate the surgical stress response. In recent years, the potential benefit of regional anaesthesia techniques for tumour recurrence has received major attention and has been discussed many times in the literature. In preparing this review, we aimed to summarize the current evidence systematically and comprehensively.


OBJECTIVES
To establish whether anaesthetic technique (general anaesthesia versus regional anaesthesia or a combination of the two techniques) influences the long-term prognosis for individuals with malignant tumours.


SEARCH METHODS
We searched The Cochrane Library (2013, Issue 12), PubMed (1950 to 15 December 2013), EMBASE (1974 to 15 December 2013), BIOSIS (1926 to 15 December 2013) and Web of Science (1965 to 15 December 2013). We handsearched relevant websites and conference proceedings and reference lists of cited articles. We applied no language restrictions.


SELECTION CRITERIA
We included all randomized controlled trials or controlled clinical trials that investigated the effects of general versus regional anaesthesia on the risk of malignant tumour recurrence in patients undergoing resection of primary malignant tumours. Comparisons of interventions consisted of (1) general anaesthesia alone versus general anaesthesia combined with one or more regional anaesthetic techniques; (2) general anaesthesia combined with one or more regional anaesthetic techniques versus one or more regional anaesthetic techniques; and (3) general anaesthesia alone versus one or more regional anaesthetic techniques. Primary outcomes included (1) overall survival, (2) progression-free survival and (3) time to tumour progression.


DATA COLLECTION AND ANALYSIS
Two review authors independently scanned the titles and abstracts of identified reports and extracted study data.All primary outcome variables are time-to-event data. If the individual trial report provided summary statistics with odds ratios, relative risks or Kaplan-Meier curves, extracted data enabled us to calculate the hazard ratio using the hazard ratio calculating spreadsheet. To assess risk of bias, we used the standard methodological procedures expected by The Cochrane Collaboration.


MAIN RESULTS
We included four studies with a total of 746 participants. All studies included adult patients undergoing surgery for primary tumour resection. Two studies enrolled male and female participants undergoing major abdominal surgery for cancer. One study enrolled male participants undergoing surgery for prostate cancer, and one study male participants undergoing surgery for colon cancer. Follow-up time ranged from nine to 17 years. All four studies compared general anaesthesia alone versus general anaesthesia combined with epidural anaesthesia and analgesia. All four studies are secondary data analyses of previously conducted prospective randomized controlled trials.Of the four included studies, only three contributed to the outcome of overall survival, and two each to the outcomes of progression-free survival and time to tumour progression. In our meta-analysis, we could not find an advantage for either study group for the outcomes of overall survival (hazard ratio (HR) 1.03, 95% confidence interval (CI) 0.86 to 1.24) and progression-free survival (HR 0.88, 95% CI 0.56 to 1.38). For progression-free survival, the level of inconsistency was high. Pooled data for time to tumour progression showed a slightly favourable outcome for the control group (general anaesthesia alone) compared with the intervention group (epidural and general anaesthesia) (HR 1.50, 95% CI 1.00 to 2.25).Quality of evidence was graded low for overall survival and very low for progression-free survival and time to tumour progression. The outcome of overall survival was downgraded for serious imprecision and serious indirectness. The outcomes of progression-free survival and time to tumour progression were also downgraded for serious inconsistency and serious risk of bias, respectively.Reporting of adverse events was sparse, and data could not be analysed.


AUTHORS' CONCLUSIONS
Currently, evidence for the benefit of regional anaesthesia techniques on tumour recurrence is inadequate. An encouraging number of prospective randomized controlled trials are ongoing, and it is hoped that their results, when reported, will add evidence for this topic in the near future.