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Correspondence  |   July 2009
Retrospective but Not Rigorous
Author Affiliations & Notes
  • Donal J. Buggy, M.D., M.Sc., D.M.E., F.R.C.P.I., F.C.A.I., F.R.C.A.
    *
  • Daniel I. Sessler, M.D.
    *
  • *Mater Misericordiae University Hospital, Dublin, Ireland.
Article Information
Correspondence
Correspondence   |   July 2009
Retrospective but Not Rigorous
Anesthesiology 7 2009, Vol.111, 203-204. doi:10.1097/ALN.0b013e3181a95b35
Anesthesiology 7 2009, Vol.111, 203-204. doi:10.1097/ALN.0b013e3181a95b35
In Reply:—
We are proponents of prospective research and between us have published more than 400 randomized trials. Randomized trials are considered the gold standard for clinical evidence because they minimize the risks of selection bias, measurement bias, confounding, and reverse causation. There are nonetheless occasions when retrospective studies are helpful. For example, retrospective studies can provide initial evidence to support a novel hypothesis and estimate the potential treatment effect.
The theory that regional analgesia may reduce the risk of cancer recurrence is both novel and recent. It is likely that a randomized trial testing this hypothesis will take 5 yr or longer, given that it will be necessary not only to enroll patients, but to wait for cancer recurrences. However, agencies are unlikely to fund such a large effort without at least some human data. Furthermore, an estimate of treatment effect is necessary to properly develop a priori  sample-size estimate and interim analysis plans. It was in this spirit that we published our current observations in men having prostate cancer surgery,1 and previous ones in women having breast cancer surgery.2 
We also wish that more details about anesthetic management were available. It is because these details would so obviously have been interesting that we commented about them in the manuscript. However, a limitation of retrospective studies is that much interesting information is often unavailable—as in our patients.
We were explicit in our recent paper, and our previous one, that small retrospective studies are no basis for changing clinical practice—and we reiterate that here. But our current1 and previous2 results, to say nothing of overwhelming animal evidence,3,4 do provide considerable basis for large randomized trials.5 The Outcomes Research Consortium has already started randomized trials of paravertebral analgesia for breast cancer and epidural analgesia for colon cancer.6 Others will start soon.
*Mater Misericordiae University Hospital, Dublin, Ireland.
References
Biki B, Mascha E, Moriarty DC, Fitzpatrick JM, Sessler DI, Buggy DJ: Anesthetic technique for radical prostatectomy surgery affects cancer recurrence: A retrospective analysis. Anesthesiology 2008; 109:180–7Biki, B Mascha, E Moriarty, DC Fitzpatrick, JM Sessler, DI Buggy, DJ
Exadaktylos AK, Buggy DJ, Moriarty DC, Mascha E, Sessler DI: Can anesthetic technique for primary breast cancer surgery affect recurrence or metastasis? Anesthesiology 2006; 4:660–4Exadaktylos, AK Buggy, DJ Moriarty, DC Mascha, E Sessler, DI
Bar-Yosef S, Melamed R, Page GG, Shakhar G, Shakhar K, Ben-Eliyahu S: Attenuation of the tumor-promoting effect of surgery by spinal blockade in rats. Anesthesiology 2001; 94:1066–73Bar-Yosef, S Melamed, R Page, GG Shakhar, G Shakhar, K Ben-Eliyahu, S
Page GG, Blakely WP, Ben-Eliyahu S: Evidence that postoperative pain is a mediator of the tumor-promoting effects of surgery in rats. Pain 2001; 90:191–9Page, GG Blakely, WP Ben-Eliyahu, S
Sessler DI: Does regional analgesia reduce the risk of cancer recurrence? A hypothesis. Eur J Cancer Prev 2008; 17:269–72Sessler, DI
Sessler DI, Ben-Eliyahu S, Mascha EJ, Parat MO, Buggy DJ: Can regional analgesia reduce the risk of recurrence after breast cancer? Methodology of a multicenter randomized trial. Contemp Clin Trials 2008; 29:517–26Sessler, DI Ben-Eliyahu, S Mascha, EJ Parat, MO Buggy, DJ