Optimal approach to elective resection for rectal cancers (COL1-2b)
Systematic review evidence[edit source]
In patients diagnosed with rectal cancer, what is the optimal resection strategy to achieve the best outcomes in terms of length and quality of life? (COL1-2b)
A systematic review was undertaken to determine the optimal resection strategy for rectal cancer to maximise survival and quality of life. The review identified studies that examined the effect of rectal cancer resection type on cancer-related outcomes including mortality, cancer-specific survival, disease-free survival, local recurrence and metastases, morbidity, complications, and other adverse events including quality of life, pain and sexual dysfunction.
Three meta-analyses comparing laparoscopic with open resection surgery were identified. All of these studies had a low risk of bias. One pooled analysis of data comparing laparoscopic with open resection surgery, with a moderate risk of bias, was also identified.
Twenty-eight level II RCTs were reported across 36 papers. Of these, 20 trials compared laparoscopic with open rectal cancer resection, and seven trials compared the following surgical interventions:
- single-port laparoscopic rectal surgery versus conventional laparoscopic surgery
- endoscopic mucosal resection with circumferential incision (CIEMR) against endoscopic mucosal resection (EMR)
- cylindrical abdominoperineal resection versus conventional abdominoperineal resection
- transanal endoscopic microsurgery versus low anterior resection
- transanal endoscopic microsurgery versus laparoscopic total mesorectal excision
- endoluminal locoregional resection versus total mesorectal excision
- laparoscopic anterior resection versus transanal endoscopic microsurgery anterior resection
Of these RCTs, one was assessed as having a low risk of bias. The remainder had an unclear or high overall risk of bias.
The search strategy, inclusion and exclusion criteria, and quality assessment are described in detail in the Technical report.
Overall survival outcomes, including 15-, 10-, 8-, 5-, 3-, and 1-year survival rates and probability, were reported in 11 RCTs in studies comparing laparoscopic with open rectal cancer resection and one meta-analysis of eight studies. Evidence consistently showed no difference between any rectal cancer resection method for these outcomes at any time point.
Three RCTs comparing laparoscopic and open resection reported disease-free survival or recurrence-free survival for stage 1–3 patients. No statistically significant differences in disease-free survival between open and laparoscopic resection groups were reported.
Perioperative/30-day/overall mortality[edit source]
Differences between laparoscopic and open surgery were non-significant for all reported mortality outcomes, including 30-day mortality, perioperative mortality, and overall (> 30 day) mortality.
Recurrence and distant metastasis[edit source]
Only one of these studies showed significant differences between groups:
- In patients with middle rectal cancer (intention-to-treat analysis) 3-year local recurrence was higher for laparoscopic resection than open resection (difference 4.1 percentage points; 90% CI 0.7 to 7.5).
- In patients with lower rectal cancer (as-treated analysis), 3-year local recurrence was lower for laparoscopic resection than open resection (difference 8.9 percentage points; 90% CI –15.6 to –2.2).
However, significance was determined through observation of 90% confidence intervals, and it is questionable whether this difference would be significant at α = 0.05.
One study comparing conventional abdominoperineal resection and cylindrical abdominoperineal resection reported no significant difference in local recurrence rates. However, numerically lower local recurrence rates were observed among patients who underwent cylindrical abdominoperineal resection.
A wide range of complication and morbidity related outcomes were reported across the studies. Very few significant differences were observed between laparoscopic and open resection patients, and these differences were not consistent overall.
Port site/wound metastases[edit source]
Seven RCTs that compared laparoscopic and open resection reported wound/port site metastases as an outcome. No significant differences were observed, with five studies reporting 0% recurrence in both groups.
Blood loss and transfusion[edit source]
Twelve RCTs comparing laparoscopic and open surgery reported significantly lower blood loss in the laparoscopic group, with significant differences ranging from 17.5 mL to 220.3 mL (p < 0.001 to p = 0.036).
Similarly, the rate of blood transfusions and amount of blood required were lower among patients who underwent laparoscopic resection in studies reporting these outcomes, including one meta-analysis.
Length of hospital stay[edit source]
Of the RCTs that compared laparoscopic and open resection, five reported significantly shorter postoperative hospital stay in the laparoscopic group, with differences ranging from 1.6 to 3.4 days (p < 0.001 to p = 0.036). Findings reported by studies that did not report statistical significance were inconsistent, with a trend towards shorter hospital stays in the laparoscopic group in five studies.
Circumferential resection margin positivity[edit source]
Nine RCTs that compared laparoscopic and open resection reported rates of positive circumferential resection margins. Six of these studies observed numerically higher rates of positive circumferential resection margins in groups who underwent open resection, while the remaining three studies observed numerically higher rates in groups who underwent laparoscopic resection. However, none of these differences were statistically significant.
Number of lymph nodes retrieved[edit source]
Of the 13 RCTs that compared open and laparoscopic resection, only one study found a significant difference in the number of lymph nodes retrieved. The remaining studies showed mixed not statistically significant differences between groups.
Sexual function[edit source]
Sexual function outcomes were reported in three RCTs that compared laparoscopic resection with open resection and one RCT that compared cylindrical abdominoperineal resection with conventional abdominoperineal resection. Although sexual function was negatively affected by any type of resection procedure, none of these studies observed significant differences between types of resection.
Fifteen RCTs that compared laparoscopic resection with open resection reported rates of conversion from laparoscopic to open surgery. Conversion rates ranged from 0 to 30.3%, with a median rate of 7.9%.
For other interventions, including transanal endoscopic microsurgery, endoluminal locoregional resection and single-port approaches, reported rates of conversion to laparoscopic anterior resection, open total mesorectal excision, and conventional laparoscopic surgery were between 5 and 11.4%.
Although a wide array of short-term and long-term complications and morbidities were reported, only two significant differences were observed:
- Open resection was associated with a higher rate of nerve injury than laparoscopic resection
- Higher rates of major postoperative complications were observed among patients undergoing total mesorectal excision, compared with those receiving endoluminal locoregional resection.
Postoperative pain[edit source]
Postoperative pain was reported by only two RCTs: one that compared laparoscopic resection with open resection and one that compared single-port resection with conventional laparoscopic resection.
The second study reported significantly lower pain scores within 3-4 days after surgery among patients who underwent single-port laparoscopic resection than among those who underwent conventional laparoscopic resection.
The search strategy, inclusion and exclusion criteria, and quality assessment are described in detail in the Technical report.
Evidence summary and recommendations[edit source]
|Laparoscopic versus open resection|
|For overall survival and mortality, there was no difference between patients undergoing laparoscopic resection and patients undergoing open resection for rectal cancer.||I, II||, , , , , , , , , , , , , , , , , , , |
|There was no statistically significant difference in rates of local recurrence, distant metastases and disease-free survival between patients having an open approach and a laparoscopic approach to rectal cancer surgery.||I, II||, , , , , , , , , , , , , , , |
|Rates of blood transfusion and the amount of perioperative blood loss were consistently and significantly lower for patients undergoing laparoscopic resection, compared with patients undergoing open rectal cancer resection.||I, II||, , , , , , , , , , , , , , , , |
|Length of hospital stay was significantly shorter for laparoscopic patients, compared with open resection patients.||I, II||, , , , , , , , , , |
|Rates of positive circumferential resection margins did not differ significantly between patients who underwent laparoscopic resection and those who underwent open resection, and reported differences did not consistently favour either approach.
||II||, , , , , |
|Differences in the number of lymph nodes retrieved between patients who underwent laparoscopic resection and those who underwent open resection were mostly not statistically significant. One study observed that significantly more lymph nodes were retrieved among the laparoscopic group.||II||, , , , , , , |
|Although sexual function was negatively affected by all surgery, no difference between patients receiving laparoscopic and open rectal cancer resection for colorectal cancer was observed.||II||, , , , |
|Comparisons between other surgical approaches|
|Transanal endoscopic microsurgery was associated with reductions in blood loss and length of hospital stay, compared with laparoscopic total mesorectal excision and low anterior resection.
No consistent significant differences between groups in were observed for survival or quality-of-life outcomes in RCTs comparing the following:
|II||, , , , |
|Of two studies that reported postoperative pain, one found that single-port laparoscopic resection was associated with significantly less pain within 3 days of surgery than conventional laparoscopic resection.||II||, |
Regardless of the approach utilised, rectal cancer resection must be undertaken by surgeons who have been appropriately trained in surgical resection of rectal cancer, utilising the principles of total mesorectal resection as proposed by Heald. This should include sharp dissection undertaken along the mesorectal plane. Surgical resection undertaken by inadequately trained surgeons is likely to result in inferior oncological outcomes.
The laparoscopic approach may have a higher potential for an inferior quality TME specimen, as demonstrated by two recent multicentre RCTs, though long-term outcome data are not yet available on these studies (Fleshman et al 2015, Stevenson et al 2015). Two other large multicentre RCTs have reported long-term outcomes with no difference in local recurrence or survival (Jeong et al 2014, Bonjer et al 2015). The surgeon should discuss with the patient the potential impact on oncological outcome of the laparoscopic approach along with the potential improvements on short term recovery.
Considerations in making these recommendations[edit source]
Laparoscopic resection of rectal cancer would be considered preferable in terms of reduced length of stay and blood loss, however case selection is important when considering whether a laparoscopic or open approach is optimal. Overall pathological equivalence has yet to be proven and in the decision over which approach is optimal for a particular case, oncological principles must not be compromised.
Long-term local recurrence and survival data for two of the recent large randomised control trials which have not demonstrated pathological equivalence between open and laparoscopic rectal resection are awaited. Long-term local recurrence and survival data are available for two other multicentre randomised controlled trials comparing open and laparoscopic rectal cancer resection which do demonstrate equivalence. Whilst laparoscopic resection appears equivalent to open resection, when undertaken by surgeons who have had appropriate training and experience, it is likely that there are some case where a laparoscopic approach is not optimal with due consideration of patient, tumour and surgeon factors.
Health system implications[edit source]
Clinical practice[edit source]
This review included RCTs from a wide range of countries, including Australia and New Zealand. Although about half of the studies were conducted in Asian populations, the evidence may be generalisable to an Australian population. However, there may be some important differences in the practice of rectal cancer resection.
Whilst laparoscopic resection of rectal cancer appears to have equivalent oncological outcomes to open surgery and some potential benefits to the patient over open surgery, it is essential that surgeons have been formally trained in laparoscopic rectal resection prior to undertaking this procedure.
There are no resource implications associated with implementing the recommendations.
Barriers to implementation[edit source]
No barriers to the implementation of these recommendations are envisaged.
Unresolved issues[edit source]
More longer-term evidence is needed from RCTs comparing survival data for laparoscopic versus open resection, especially from recent multicentre RCT trials.
RCT evidence regarding the role of alternative approaches, such robotic resection or transanal total mesorectal excision, is required before conclusions can be made on their role.
Studies currently underway[edit source]
Results are awaited on the ROLARR trial comparing laparoscopic versus robotic resection of rectal cancer. However no data have yet been published.
COLOR III, a RCT comparing laparoscopic resection versus transanal total mesorectal excision, is currently recruiting.
Future research priorities[edit source]
Evidence comparing longer-term survival data and alternative approaches would be valuable.
- Arezzo A, Passera R, Scozzari G, Verra M, Morino M. Laparoscopy for rectal cancer reduces short-term mortality and morbidity: results of a systematic review and meta-analysis. Surg Endosc 2013 May;27(5):1485-502 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23183871.
- Vennix S, Pelzers L, Bouvy N, Beets GL, Pierie JP, Wiggers T, et al. Laparoscopic versus open total mesorectal excision for rectal cancer. Cochrane Database Syst Rev 2014 Apr 15;(4):CD005200 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24737031.
- Zhao D, Li Y, Wang S, Huang Z. Laparoscopic versus open surgery for rectal cancer: a meta-analysis of 3-year follow-up outcomes. Int J Colorectal Dis 2016 Apr;31(4):805-11 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26847617.
- Ng SS, Lee JF, Yiu RY, Li JC, Hon SS, Mak TW, et al. Long-term oncologic outcomes of laparoscopic versus open surgery for rectal cancer: a pooled analysis of 3 randomized controlled trials. Ann Surg 2014 Jan;259(1):139-47 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23598381.
- Braga M, Frasson M, Vignali A, Zuliani W, Capretti G, Di Carlo V. Laparoscopic resection in rectal cancer patients: outcome and cost-benefit analysis. Dis Colon Rectum 2007 Apr;50(4):464-71 Available from: http://www.ncbi.nlm.nih.gov/pubmed/17195085.
- van der Pas MH, Haglind E, Cuesta MA, Fürst A, Lacy AM, Hop WC, et al. Laparoscopic versus open surgery for rectal cancer (COLOR II): short-term outcomes of a randomised, phase 3 trial. Lancet Oncol 2013 Mar;14(3):210-8 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23395398.
- Bonjer HJ, Deijen CL, Haglind E, COLOR II Study Group. A Randomized Trial of Laparoscopic versus Open Surgery for Rectal Cancer. N Engl J Med 2015 Jul 9;373(2):194 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26154803.
- Veenhof AA, Sietses C, von Blomberg BM, van Hoogstraten IM, vd Pas MH, Meijerink WJ, et al. The surgical stress response and postoperative immune function after laparoscopic or conventional total mesorectal excision in rectal cancer: a randomized trial. Int J Colorectal Dis 2011 Jan;26(1):53-9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20922542.
- Andersson J, Abis G, Gellerstedt M, Angenete E, Angerås U, Cuesta MA, et al. Patient-reported genitourinary dysfunction after laparoscopic and open rectal cancer surgery in a randomized trial (COLOR II). Br J Surg 2014 Sep;101(10):1272-9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24924798.
- Andersson J, Angenete E, Gellerstedt M, Angerås U, Jess P, Rosenberg J, et al. Health-related quality of life after laparoscopic and open surgery for rectal cancer in a randomized trial. Br J Surg 2013 Jun;100(7):941-9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23640671.
- Ng SS, Lee JF, Yiu RY, Li JC, Hon SS, Mak TW, et al. Laparoscopic-assisted versus open total mesorectal excision with anal sphincter preservation for mid and low rectal cancer: a prospective, randomized trial. Surg Endosc 2014 Jan;28(1):297-306 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24013470.
- Ng SS, Leung KL, Lee JF, Yiu RY, Li JC, Hon SS. Long-term morbidity and oncologic outcomes of laparoscopic-assisted anterior resection for upper rectal cancer: ten-year results of a prospective, randomized trial. Dis Colon Rectum 2009 Apr;52(4):558-66 Available from: http://www.ncbi.nlm.nih.gov/pubmed/19404053.
- Ng SS, Leung KL, Lee JF, Yiu RY, Li JC, Teoh AY, et al. Laparoscopic-assisted versus open abdominoperineal resection for low rectal cancer: a prospective randomized trial. Ann Surg Oncol 2008 Sep;15(9):2418-25 Available from: http://www.ncbi.nlm.nih.gov/pubmed/18392659.
- Kang SB, Park JW, Jeong SY, Nam BH, Choi HS, Kim DW, et al. Open versus laparoscopic surgery for mid or low rectal cancer after neoadjuvant chemoradiotherapy (COREAN trial): short-term outcomes of an open-label randomised controlled trial. Lancet Oncol 2010 Jul;11(7):637-45 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20610322.
- Jeong SY, Park JW, Nam BH, Kim S, Kang SB, Lim SB, et al. Open versus laparoscopic surgery for mid-rectal or low-rectal cancer after neoadjuvant chemoradiotherapy (COREAN trial): survival outcomes of an open-label, non-inferiority, randomised controlled trial. Lancet Oncol 2014 Jun;15(7):767-74 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24837215.
- Liang X, Hou S, Liu H, Li Y, Jiang B, Bai W, et al. Effectiveness and safety of laparoscopic resection versus open surgery in patients with rectal cancer: a randomized, controlled trial from China. J Laparoendosc Adv Surg Tech A 2011 Jun;21(5):381-5 Available from: http://www.ncbi.nlm.nih.gov/pubmed/21395453.
- Lujan J, Valero G, Hernandez Q, Sanchez A, Frutos MD, Parrilla P. Randomized clinical trial comparing laparoscopic and open surgery in patients with rectal cancer. Br J Surg 2009 Sep;96(9):982-9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/19644973.
- Green BL, Marshall HC, Collinson F, Quirke P, Guillou P, Jayne DG, et al. Long-term follow-up of the Medical Research Council CLASICC trial of conventional versus laparoscopically assisted resection in colorectal cancer. Br J Surg 2013 Jan;100(1):75-82 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23132548.
- Guillou PJ, Quirke P, Thorpe H, Walker J, Jayne DG, Smith AM, et al. Short-term endpoints of conventional versus laparoscopic-assisted surgery in patients with colorectal cancer (MRC CLASICC trial): multicentre, randomised controlled trial. Lancet 2005 May;365(9472):1718-26 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15894098.
- Jayne DG, Brown JM, Thorpe H, Walker J, Quirke P, Guillou PJ. Bladder and sexual function following resection for rectal cancer in a randomized clinical trial of laparoscopic versus open technique. Br J Surg 2005 Sep;92(9):1124-32 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15997446.
- Jayne DG, Guillou PJ, Thorpe H, Quirke P, Copeland J, Smith AM, et al. Randomized trial of laparoscopic-assisted resection of colorectal carcinoma: 3-year results of the UK MRC CLASICC Trial Group. J Clin Oncol 2007 Jul 20;25(21):3061-8 Available from: http://www.ncbi.nlm.nih.gov/pubmed/17634484.
- Taylor GW, Jayne DG, Brown SR, Thorpe H, Brown JM, Dewberry SC, et al. Adhesions and incisional hernias following laparoscopic versus open surgery for colorectal cancer in the CLASICC trial. Br J Surg 2010 Jan;97(1):70-8 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20013936.
- Zhou ZG, Hu M, Li Y, Lei WZ, Yu YY, Cheng Z, et al. Laparoscopic versus open total mesorectal excision with anal sphincter preservation for low rectal cancer. Surg Endosc 2004 Aug;18(8):1211-5 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15457380.
- Arteaga González I, Díaz Luis H, Martín Malagón A, López-Tomassetti Fernández EM, Arranz Duran J, Carrillo Pallares A. A comparative clinical study of short-term results of laparoscopic surgery for rectal cancer during the learning curve. Int J Colorectal Dis 2006 Sep;21(6):590-5 Available from: http://www.ncbi.nlm.nih.gov/pubmed/16292517.
- Fleshman J, Branda M, Sargent DJ, Boller AM, George V, Abbas M, et al. Effect of Laparoscopic-Assisted Resection vs Open Resection of Stage II or III Rectal Cancer on Pathologic Outcomes: The ACOSOG Z6051 Randomized Clinical Trial. JAMA 2015 Oct 6;314(13):1346-55 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26441179.
- Fujii S, Ishibe A, Ota M, Yamagishi S, Watanabe K, Watanabe J, et al. Short-term results of a randomized study between laparoscopic and open surgery in elderly colorectal cancer patients. Surg Endosc 2014 Feb;28(2):466-76 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24122242.
- Stevenson AR, Solomon MJ, Lumley JW, Hewett P, Clouston AD, Gebski VJ, et al. Effect of Laparoscopic-Assisted Resection vs Open Resection on Pathological Outcomes in Rectal Cancer: The ALaCaRT Randomized Clinical Trial. JAMA 2015 Oct 6;314(13):1356-63 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26441180.
- Gong J, Shi DB, Li XX, Cai SJ, Guan ZQ, Xu Y. Short-term outcomes of laparoscopic total mesorectal excision compared to open surgery. World J Gastroenterol 2012 Dec 28;18(48):7308-13 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23326138.
- Pecorelli N, Amodeo S, Frasson M, Vignali A, Zuliani W, Braga M. Ten-year outcomes following laparoscopic colorectal resection: results of a randomized controlled trial. Int J Colorectal Dis 2016 Jul;31(7):1283-90 Available from: http://www.ncbi.nlm.nih.gov/pubmed/27090804.
- Chen YY, Liu ZH, Zhu K, Shi PD, Yin L. Transanal endoscopic microsurgery versus laparoscopic lower anterior resection for the treatment of T1-2 rectal cancers. Hepatogastroenterology 2013 Jun;60(124):727-32 Available from: http://www.ncbi.nlm.nih.gov/pubmed/23159393.
- Lezoche E, Baldarelli M, Lezoche G, Paganini AM, Gesuita R, Guerrieri M. Randomized clinical trial of endoluminal locoregional resection versus laparoscopic total mesorectal excision for T2 rectal cancer after neoadjuvant therapy. Br J Surg 2012 Sep;99(9):1211-8 Available from: http://www.ncbi.nlm.nih.gov/pubmed/22864880.
- Lezoche E, Guerrieri M, Paganini AM, D'Ambrosio G, Baldarelli M, Lezoche G, et al. Transanal endoscopic versus total mesorectal laparoscopic resections of T2-N0 low rectal cancers after neoadjuvant treatment: a prospective randomized trial with a 3-years minimum follow-up period. Surg Endosc 2005 Jun;19(6):751-6 Available from: http://www.ncbi.nlm.nih.gov/pubmed/15868260.
- Lezoche G, Baldarelli M, Guerrieri M, Paganini AM, De Sanctis A, Bartolacci S, et al. A prospective randomized study with a 5-year minimum follow-up evaluation of transanal endoscopic microsurgery versus laparoscopic total mesorectal excision after neoadjuvant therapy. Surg Endosc 2008 Feb;22(2):352-8 Available from: http://www.ncbi.nlm.nih.gov/pubmed/17943364.
- Bulut O, Aslak KK, Levic K, Nielsen CB, Rømer E, Sørensen S, et al. A randomized pilot study on single-port versus conventional laparoscopic rectal surgery: effects on postoperative pain and the stress response to surgery. Tech Coloproctol 2015 Jan;19(1):11-22 Available from: http://www.ncbi.nlm.nih.gov/pubmed/25380743.
- Han JG, Wang ZJ, Wei GH, Gao ZG, Yang Y, Zhao BC. Randomized clinical trial of conventional versus cylindrical abdominoperineal resection for locally advanced lower rectal cancer. Am J Surg 2012 Sep;204(3):274-82 Available from: http://www.ncbi.nlm.nih.gov/pubmed/22920402.
- Huang J, Lu ZS, Yang YS, Yuan J, Wang XD, Meng JY, et al. Endoscopic mucosal resection with circumferential incision for treatment of rectal carcinoid tumours. World J Surg Oncol 2014 Jan 28;12:23 Available from: http://www.ncbi.nlm.nih.gov/pubmed/24472342.
- Chen Y, Guo R, Xie J, Liu Z, Shi P, Ming Q. Laparoscopy Combined With Transanal Endoscopic Microsurgery for Rectal Cancer: A Prospective, Single-blinded, Randomized Clinical Trial. Surg Laparosc Endosc Percutan Tech 2015 Oct;25(5):399-402 Available from: http://www.ncbi.nlm.nih.gov/pubmed/26429049.
- Liu FL, Lin JJ, Ye F, Teng LS. Hand-assisted laparoscopic surgery versus the open approach in curative resection of rectal cancer. J Int Med Res 2010 May;38(3):916-22 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20819427.
- Jayne DG, Thorpe HC, Copeland J, Quirke P, Brown JM, Guillou PJ. Five-year follow-up of the Medical Research Council CLASICC trial of laparoscopically assisted versus open surgery for colorectal cancer. Br J Surg 2010 Nov;97(11):1638-45 Available from: http://www.ncbi.nlm.nih.gov/pubmed/20629110.