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Clinical Update - Breast Cancer

Clinical Update Issue 21 - August 2005 - ISSN 1328-9454 See previous editions

EFFICACY OF PROPHYLACTIC MASTECTOMY IN WOMEN WITH UNILATERAL BREAST CANCER

Commentary by Professor Christobel Saunders

The article:

Herrinton LJ, Barlow WE, Yu O et al. Efficacy of prophylactic mastectomy in women with unilateral breast cancer: A Cancer Research Network Project. Journal of Clinical Oncology 2005; 23(19): 4275-4286

Reviewer:

Professor Christobel Saunders is Professor of Surgical Oncology at the University of WA. She is also a breast surgeon at the Royal Perth and Sir Charles Gairdner hospitals.

In this issue...

• Article summary
• What does this article add to existing clinical evidence in this area?
• How adequate was the methodology used in addressing the aims of the study?
• What are the implications of the study for clinical practice in Australia?

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Summary

Abbreviations

Contralateral Prophylactic Mastectomy (CPM); Health Maintenance Organisations (HMOs); Hazard Ratio (HR); Confidence Interval (CI);

Study design

A retrospective cohort study of women diagnosed with unilateral breast cancer between 1979 and 1999, comparing women who underwent CPM with women who did not. The primary outcomes were contralateral breast cancer incidence and breast cancer mortality. Two different analyses were used to examine the effect of CPM on contralateral breast cancer and breast cancer mortality.

• Contralateral breast cancer: 1,072 women were identified as having CPM out of 56,400 women diagnosed with breast cancer between 1979 and 1999 from six HMOs. A comparative sample of 317 women was taken from the remaining women who did not undergo CPM.
• Breast cancer mortality: 908 women were identified as having CPM out of 47,276 women diagnosed with breast cancer between 1979 and 1999 from four of the six HMOs.

Descriptive characteristics of the women were reported, including the extent of disease, details of initial treatment undertaken and family history of breast or ovarian cancer. Median follow-up was 5.7 years for women who underwent CPM and 4.8 years for those who did not.

Findings

The risk of subsequent contralateral breast cancer was reduced in women who underwent CPM compared with similar women who did not undergo CPM (0.5% vs 2.7%; HR = 0.03*, 95% CI = 0.006 to 0.13).

Breast cancer mortality was lower in women who underwent CPM compared with those who did not undergo CPM (8.1% vs 11.7%; HR = 0.57*, 95% CI = 0.45 to 0.72).

Non-breast cancer mortality was also lower in women who underwent CPM (4.6% vs 8.7%; HR = 0.78*, 95% CI = 0.57 to 1.06) as was all-cause mortality (13.0% vs 20.5%; HR = 0.60*, 95% CI = 0.50 to 0.72) compared to women who did not undergo CPM.

*HR determined after adjustment for breast cancer characteristics and treatment

Conclusion

The authors concluded that CPM seems to protect against the development of contralateral breast cancer. Although women who underwent CPM had relatively low all-cause mortality, CPM was also associated with decreased breast cancer mortality.

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What does this article add to existing clinical evidence in this area?

This paper addresses a question that is often one of the first our patients ask us: “should I have my other breast removed as well?”. Women often wish to consider this for a variety of reasons, including as an initial reaction to the shock of a life-threatening illness, but also, after some contemplation, as a reaction to the perceived threat of a second cancer, particularly in women with a strong family history of the disease. Whether or not to undergo prophylactic mastectomy is a complex decision in which women must make choices about more extensive surgery, future surveillance difficulties, development of a second primary and body image. Yet, to date, there have been little data on how this procedure may alter survival. This large study is the first to give an indication that CPM may not only decrease the chance of a second breast cancer (as would be expected) by around 97%, but may improve disease-specific survival with an absolute reduction in death of about 4%.

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How adequate was the methodology used in addressing the aims of the study?

Although this study was large and painstakingly carried out, it is unlikely to be robust enough in its methodology to really change current clinical practice. It is retrospective and because of this the two groups – those who underwent CPM and those who did not – are not well matched. Many of those in the non-CPM group had breast conservation and it appears from the relatively high number of deaths from other causes in the non-CPM group, that these women had many more co-morbidities (thus it may be that healthier women are advised to have CPM). Moreover there was a relatively low rate of hormone therapy use (probably reflecting the era in which patients were treated) and this did not seem to protect against contralateral cancer as much as randomised controlled trials have shown hormone therapy can. A longer follow-up than 5.7 years may be needed to show a benefit.

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What are the implications of the study for clinical practice in Australia?

Contralateral breast cancer occurs in between 2% and 20% of women who have had one tumour. There are a number of factors, including age and family history, which may increase the risk of contralateral breast cancer. The decision to undergo CPM is one that should take into account both these factors and the concerns and priorities of the patient. The risk reduction benefits of adjuvant systemic treatment, in particular hormone therapy, also need to be considered, and the short- and long-term harms, as well as benefits, discussed with the patient – CPM is a final decision and decision regret an under-explored area. Without harder evidence from randomised studies, this paper is unlikely in itself to alter our practice in Australia, but does further reinforce the importance of discussing all options for treatment with the patient, and helping her come to a choice which suits her needs.

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Disclaimer:
Clinical Update is produced by the National Breast Cancer Centre (NBCC) and is intended to provide health professionals with timely expert commentary on new research in breast cancer. Commentaries included in Clinical Update do not replace recommendations included in NBCC clinical practice guidelines.
Information contained in Clinical Update is not intended to be used as substitute for an independent health professional's advice. The NBCC does not accept any liability for any injury, loss or damage incurred by use of or reliance on the information contained in Clinical Update. The NBCC develops material based on the best available evidence however cannot guarantee and assumes no legal liability or responsibility for the currency or completeness of the information.

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