Rates of breast cancer surgery in Canada from 2007/08 to 2009/10: retrospective cohort study

The issue of variation in quality of breast cancer care across Canada is an important one. Porter et al. (2014) reported a wide variation in mastectomy rates across provinces[1]. The major strength of this study is its comprehensive examination of breast cancer surgery rates in a population-based cohort over a contemporary time period. Media attention has focused on the high rates of mastectomy in Newfoundland and Labrador (NL), the finding that less affluent women were more likely to have a mastectomy, and the question of access to radiation facilities as a deciding factor[2,3]. In the study, when adjustments were made for distance to radiation facility, age, and neighbourhood income quintile, the final mastectomy rate for NL dropped from 69% to 61%. Other provinces changed by 0 to 6% after adjustment. While these three variables showed statistically significant contributions to provincial variation, a lot of unexplained variation remains. The final range of mastectomy rates across provinces was 35% to 61%. Between the highest and lowest provincial rates, there is a 26% difference that cannot be attributed to age, income, or travel requirements.

There are two discussions that are lacking in this article: the issue of geographical variation in eligibility for breast-conserving surgery (BCS), and the issue of choice among those eligible for BCS. (The focus of the present letter is on the former). Firstly, the authors acknowledge as a limitation the fact that clinical and histopathological variables were not taken into account, such as tumour size, stage, or BRCA gene mutation status. The authors dismiss the potentially important role of staging data in particular. Porter et al. state: "...it is unlikely that stage distribution alone accounts for the observed mastectomy rate, because recently published analyses have shown generally comparable stage distribution across provinces (CPAC 2012)."(p. E107). This interpretation of findings of the Breast Cancer Control in Canada report published in 2012 by the Canadian Partnership Against Cancer[4] is inadequate and misleading, despite the fact that this report was co-written and/or edited by four of the authors of the Porter et al. paper. In the 2012 CPAC report, rates of later stage diagnoses were clearly higher in NL than in other provinces: "Some interprovincial variation in breast cancer stage distribution is evident. In 2010, Newfoundland and Labrador had a higher percentage (27%) diagnosed with advanced disease (Stage III or IV) relative to the average of 19% for all nine provinces with stage data (as a percentage of women diagnosed with invasive breast cancer)."4 (p. 36). Thus, fewer NL women would have been eligible for BCS given the higher percentage of later stage diagnosis. Other uncontrolled factors may contraindicate for BCS, including menopausal status, lifestyle factors, and comorbidities such as Type 2 diabetes or coronary heart disease[5]. Finally, the authors fail to address the absence of psychosocial and other non-clinical variables which previous research has shown to affect choice of mastectomy versus BCS among eligible women[6-9].

This study could be greatly improved by linking to staging data. It is unclear why this step was not taken. CPAC (2012) reported that staging data were captured for 87.9% of breast cancer cases in NL in 2009 and for 98.7% of cases in 2010[4]; some staging data is likely available for earlier years as well.

The notion that a high mastectomy rate is a marker of poorer treatment has not been demonstrated. Poor quality treatment would be occurring if patients who qualified for breast conservation were not offered it. This outcome cannot be measured by mastectomy rates alone. Many potential confounding variables remain, even after adjustment for age, income, and distance from a radiation facility. In summary, the Porter et al. article is hypothesis generating but does not answer the important questions about quality of surgical care in breast cancer in Canada. Are eligible patients being offered BCS and mastectomy? This is the important question.

References

1. Porter G, Wagar B, Bryant H, Hewitt M, Wai E, Dabbs K, et al. Rates of breast cancer surgery in Canada from 2007/08 to 2009/10: retrospective cohort study. CMAJ Open 2014;2(2):E102-108.

2. Mastectomy rates vary greatly across Canada: Geography and income among factors associated with differences in breast cancer surgeries. CBC News 2014, June 17. Available at: http://www.cbc.ca/news/health/mastectomy- rates-vary-greatly-across-canada-1.2678272 (Accessed October 1, 2014).

3. Breast Cancer Surgery Rates Vary Greatly in Canada. U.S. News & World Report 2014, June 18. Available at: http://health.usnews.com/health -news/articles/2014/06/18/breast-cancer-surgery-rates-vary-greatly-in- canada (Accessed March 4, 2015).

4. Canadian Partnership Against Cancer (2012). Breast Cancer Control in Canada: A System Performance Special Focus Report. Toronto, Canadian Partnership Against Cancer.

5. Yancik, R, Wesley, MN, Ries, LA, Havlik, RJ, Edwards, BK, & Yates, JW (2001). Effect of age and comorbidity in postmenopausal breast cancer patients aged 55 years and older. Jama, 285(7), 885-892.

6. Cao JQ, Truong PT, Olivotto IA, Olson R, Coulombe G, Keyes M, et al. Should Women Younger Than 40 Years of Age With Invasive Breast Cancer Have a Mastectomy?: 15-Year Outcomes in a Population-Based Cohort. Int J Radiation Oncol Biol Phys 2014; 90(3), 509-17.

7. Covelli AM, Baxter NN, Fitch MI, McCready DR, Wright FC. 'Taking Control of Cancer': Understanding Women's Choice for Mastectomy. Ann Surg Oncol. Published online 2014 Sep 5; DOI: 10.1245/s10434-014-4033-7.

8. Hawley ST, Jagsi R, Morrow M, Janz NK, Hamilton A, Graff JJ, Katz SJ. Social and Clinical Determinants of Contralateral Prophylactic Mastectomy. JAMA Surg. Published online 2014 May 21. DOI: 10.1001/jamasurg.2013.5689.

9. Ristevski E, Regan M, Birks D, Steers N, Byrne A. A qualitative study of rural women's views for the treatment of early breast cancer. Health Expect. Published online 2014 Sep 29. DOI: 10.1111/hex.12277.

The author wishes to acknowledge Dr. Alex Mathieson, Departments of Surgery and Oncology, Memorial University of Newfoundland, for providing knowledge and guidance on clinical relevance, and Lian Shi, Memorial University, for providing discussion and review.

Conflict of Interest:

None declared