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Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial

BMJ 2014; 348 doi: https://doi.org/10.1136/bmj.g366 (Published 11 February 2014) Cite this as: BMJ 2014;348:g366

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Re: Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial

Perhaps the authors of this study and the editors of this journal had not completed their training when the first publications relating to the study began to be published in the early 1990’s. At that time there was considerable criticism about the randomization of patients in the study. (1-5) The study was actually designed to evaluate the value of mammography in women ages 40 to 49. It was found that there was an excess of patients with advanced cancer found in women aged 40 -49 allocated to the mammography group. Tarone (5) noted that an excess of women with four or more positive nodes in the mammography group would not have arisen by chance if random allocation had been followed. It was subsequently revealed by nurses participating in the study that women with breast complaints were put in the mammography group.

In the current publication related to this study it is reported that 68 percent of the cancers in the mammography group were palpable. How is this possible? In addition there was little difference in the mean tumor size or in nodal involvement.

In my own practice the 681 invasive cancers detected on mammography average 6 mm in diameter compared to 13 mm for the 640 cancers detected by clinical examination. Nodal involvement in my patients is 19 percent if the cancer is detected on mammography compared to 39 percent if found on clinical examination. Eighty-five percent of my patients with cancers detected on mammography are treated with breast conservation compared to 77 percent of those detected on clinical examination. Ten year disease-free survival for my patients with mammographically detected cancers is 92 percent compared to 82 percent if the cancer was detected on clinical examination. My results are not exceptional.

The authors of the Canadian study, knowing full well that the randomization was flawed, are being unethical in publishing these results without mention of the early criticisms.

1. Mettlin CJ, Smart CR. The Canadian National Breast Screening Study. Cancer 1993; 72 (Suppl): 1461-1465.

2. Conseil d’Evaluation des Technologies de la Santes (CETS). Screening for breast cancer in women 40-49 years. Montreal: CETS; 1993.

3. Kopans DB, Feig SA. The Cannadian National Breast Screening Study: A critical review. Am J Roentgenol 1993; 161: 755-760.

4. Baines CJ. The Canandian National Breast Screening Study: A perspective on criticisms. Ann Intern Med 1994;,120:326-334.

5. Tarone RE. The excess of patients with advance cancer in young women screened with mammography in the Canadian National Breast Screening Study. Cancer 1995; 75: 997-1003.

Competing interests: No competing interests

14 February 2014
Paul I Tartter
Physician
Mount Sinai Roosevelt Division
425 West 59th Street, 7A, New York, N.Y. 10019