Trouble from a Literary Reference

Abstract

Our fax numbers: 617-739-9864 and 617-734-4457Our e-mail address: letters@nejm.orgWe cannot acknowledge receipt of your letter, but we will notify you when we have made a decision about publication. We are unable to provide prepublication proofs. Please enclose a stamped, self-addressed envelope if you want unpublished material returned to you. Financial associations or other possible conflicts of interest must be disclosed. Submission of a letter constitutes permission for the Massachusetts Medical Society, its licensees, and its assignees to use it in the Journal' s various editions (print, data base, and optical disk) and in anthologies, revisions, and any other form or medium.998 · S eptember 23, 19 9 9The New Eng land Jour nal of Medicine Correspondence Treatment of Ductal Carcinoma in SituTo the Editor: The article by Silverstein et al. (May 13 issue) 1 on the influence of margin width on local recurrence in patients with ductal carcinoma in situ who were treated with breast-conserving therapy provides no data showing that margins (of any size) were associated with outcome in their patients. The authors define subgroups of patients according to margin width without ever proving that margins were statistically important in univariate or multivariate analysis. We are left to guess whether margins were related to outcome as a continuous variable and how the three subgroups of patients (defined according to margin width) were selected. Instead, the "multivariate analysis" examines only two variables at a time: the use of radiation therapy and one other prognostic variable within each of the three margin-width subgroups. Without a multivariate analysis that simultaneously includes all the variables that might be related to local recurrence, we can only speculate whether the authors have analyzed their results incorrectly or whether their conclusions are biased.It is also unclear why we are not given information on the length of follow-up in the subgroups of patients defined according to margin width. Since patients treated after 1989 generally did not receive radiation therapy and the extent of resection appears to have increased after this date, it is only logical to assume that follow-up may be substantially shorter for patients with large margins who did not receive radiation therapy. In fact, we are told that patients who received radiation therapy had almost 2 more years of follow-up than patients who underwent only excision: 92 as compared with 72 months, respectively.In patients treated with breast-conserving therapy, two types of recurrences can develop, which are biologically unrelated. They are a recurrence of the treated index lesion and independent development of a separate cancer elsewhere in the breast. If these two events are then combined and analyses are performed, the dilutional effect of these unrelated new cancers may obscure possible statistical associations. 2 Finally, the suggestion that patients with margins from 1 to less than 10 mm wide are a homogeneous group who will respond uniforml...