NBSS: opportunity to compromise the process
CMAJ 1997;157:247
See response by: A.B. Miller, C.J. Baines, T. To
In 1995 I wrote to Drs. John C. Bailar III and Brian MacMahon, emphasizing to both the need to interview the individuals involved in random allocation in the National Breast Screening Study (NBSS). As the authors point out in their article "Randomization in the Canadian National Breast Screening Study: a review for evidence of subversion" (CMAJ 1997;156:193-9 [full text / résumé]), there was opportunity to compromise the process, since the lists were open and multiple allocation numbers were frequently obtained ahead of time. As a result, lines could be skipped without any need for erasures or alterations. The most direct way to find out whether the process was compromised would be to ask those involved in the allocation and to provide them with anonymity and protection from retribution. This was not done. Consequently, the authors' review adds little to what is already known.
The reviewers confine themselves to evaluating 3 centres. Given that allocations were supposedly random and given the relatively small number of deaths due to cancer at each centre, the problems may not have occurred in the centres where the allocations appeared to be "imbalanced"; they may well have occurred in the centres where the allocations appeared "balanced."
Adding to the already large number of problems with the NBSS was the revelation by Dr. Anthony B. Miller at the recent US National Institutes of Health (NIH) Consensus Development Conference, held in Bethesda, Md., Jan. 2123, 1997, that the control group was apparently treated differently, in community centres, than the screened group, which was treated in larger centres. The women with cancer in the control group apparently had fewer and less extensive axillary dissections. This adds another imbalance to the NBSS.
In the abstracts printed by the NIH for the conference, Miller wrote that "the number of breast cancer deaths are now 52 in each arm." At the meeting, he stated that this had been a "mistake" and that there were 82 deaths among the screened women and 67 among the controls. An independent review of the linkage and follow-up of deaths due to breast cancer in the NBSS should be undertaken to ascertain whether there are other "mistakes."
Finally, I have been identified as the major critic of the NBSS, although numerous others have written and lectured on the same problems.17 I have been struck, however, by the fact that only a few researchers directly involved with the NBSS have publicly defended the trial. Had I been a radiologist involved in the NBSS, and confident in what had transpired, I would have argued strenuously in support of the methods and results of the trial. I find the absence of such support surprising.
Daniel B. Kopans, MD
Massachusetts General Hospital
Harvard Medical School
Boston, Mass.
References
- Moskowitz M. Author of Canadian breast cancer study retracts warnings [letter].
J Natl Cancer Inst 1992;84:1368-71.
- Yaffe MJ. Correction: Canada study [letter]. J Natl Cancer Inst 1993;85:94.
- Burhenne LJW, Burhenne HJ. The Canadian National Breast Screening Study: a Canadian critique. Am J Roentgenol 1993;161:761-3.
- Sickles EA, Kopans DB. Deficiencies in the analysis of breast cancer screening data. J Natl Cancer Inst 1993;85:1621-4.
- Kopans DB, Feig SA. The Canadian National Breast Screening Study: a critical review. Am J Roentgenol 1993;161:755-60.
- Boyd NF, Jong RA, Yaffe MJ, Tritchler D, Lockwood G, Zylak CJ. A critical appraisal of the Canadian National Breast Cancer Screening Study. Radiology 1993;189:661-3.
- Tarone RE. The excess of patients with advanced breast cancers in young women screened with mammography in the Canadian National Breast Screening Study. Cancer 1995;75:997-1003.
 |
Send a letter to the editor responding to this article
Envoyez une lettre à la rédaction au sujet de cet article |
Letters