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Do Some Breast Cancers Disappear?

Provocative Norwegian study results suggest that the answer is yes.

We know little about the natural history of untreated breast cancer. In a prospective cohort study, investigators took advantage of the introduction of biennial mammography screening in four Norwegian counties and compared 6-year cumulative incidences of invasive breast cancer before and after regular screening became available. The screened cohort consisted of women (age range when screening began, 50–64) who underwent biennial screening mammograms. Women in the age-matched control cohort (for which follow-up began 4 years before the screening program was initiated) each underwent a single prevalence screening mammogram at the end of their 6-year follow-up. The primary outcome, invasive breast cancer, was ascertained through the Norwegian cancer registry.

The 6-year cumulative incidence of invasive breast cancer was 1909 (screened cohort) and 1564 (control) per 100,000 women (relative rate, 1.22; 95% confidence interval, 1.16–1.30). Because the prevalence screen could have missed some cancers, the authors assessed cumulative breast cancer incidence after 8 years of follow-up in both cohorts; by then, the screened cohort had undergone four screening mammograms, and the control cohort had experienced 4 years without screening followed by two screening mammograms during the next 4 years. The findings were similar in this extended analysis (RR, 1.20; 95% CI, 1.14–1.25). The authors explained why they believed that their overall findings did not result from changes in cancer registry case ascertainment, rising sensitivity of screening mammograms, or shifts in use of hormone therapy.

Comment: Spontaneous regression of renal cancers and melanomas has been reported, but few studies have addressed natural regression of breast cancer. These authors interpret their findings to mean that, because cumulative breast cancer incidence among controls did not reach that of the screened group, some invasive breast cancers that are found with serial mammography would not persist to be detectable with one prevalence screen at 6 years — in other words, some invasive breast cancers spontaneously regressed. The authors point out that, in randomized trials of mammography, serial screens yielded excess invasive breast cancer diagnoses of about 20%, similar to the present findings. As an editorialist notes, if the authors’ hypothesis is correct, breast cancer mortality (not evaluated in this report) should not differ between the two cohorts. If the findings of this study can be confirmed — and if we learn how to predict which tumors will regress spontaneously — future approaches to breast cancer might allow some women to forgo treatment in favor of monitoring.

— Andrew M. Kaunitz, MD

Published in Journal Watch Women's Health December 18, 2008

Citation(s):

Zahl P-H et al. The natural history of invasive breast cancers detected by screening mammography. Arch Intern Med 2008 Nov 24; 168:2311.

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• Medline abstract (Free)

Kaplan RM and Porzsolt F. The natural history of breast cancer. Arch Intern Med 2008 Nov 24; 168:2302.

• Original article (Subscription may be required)
• Medline abstract (Free)