The Canadian Centre for Applied Research in Cancer Control

A population cohort on contralateral prophylactic mastectomy: a concern for over-aggressive treatment of breast cancer patients in Canada

Lead Researcher(s):  Angel Arnaout

Lead Institution: Ottawa Hospital Research Institute

Co-Investigators: Janet Squires, Carl Van Walraven, Mark Clemons

ARCC Program Area(s): Health Systems, Services, and Policy

Funding Term: 2017

Project Summary:

Breast cancer is the most common cancer in Canadian women with over 24,000 diagnosed annually. Contralateral prophylactic mastectomy (CPM) is the removal of the other, non-cancerous breast in a patient with known unilateral breast cancer. The low incidence of contralateral breast cancer, the lack of survival benefit of CPM, and the increased morbidity from having CPM do not justify its use in the majority of women with unilateral breast cancer. As such, international evidence-based guidelines “strongly discourage” the use of CPM in most women with unilateral breast cancer. Studies in the US have demonstrated a sharp increase in CPM in the recent years as an ‘overaggressive’ treatment of unilateral breast cancer. No study exists to demonstrate similar trends in Canada on a large scale, although small reports have suggested it.


  1. to describe the trend in the rates of unilateral and bilateral mastectomy in women diagnosed with unilateral breast cancer in Ontario
  2. to describe the factors associated with having a unilateral versus bilateral mastectomy to treat unilateral breast cancer.

In the last two years, our team has successfully obtained two knowledge translation grants on the topic of CPM

(Ontario Institute of Cancer Research/Cancer Care Ontario KT-Net Grant and the Canadian Cancer Society KT-A Grant) to address the enablers and barriers of performing CPM. We have conducted and recently completed semi-structured interviews with knowledge user groups across Canada (patients and health-care providers involved are: breast surgeons, plastic surgeons, medical and radiation oncologists, nurses). Based on the results of our interviews, we have recently designed a multifaceted KT intervention in efforts to reduce this non-evidence based practice. This multifaceted KT intervention involves educational outreach, development of Canadian National Consensus Guidelines on CPM, and a decision aid tool for patients. Based on the findings of this study, we can now identify geographic, socioeconomic, demographic, and practice set-up factors that contribute to the problem of rising CPM use in Canada. This knowledge of geographic variability in CPM rates can now help us tailor our KT interventions to the local contexts of different regions; and more effectively target our intervention and dissemination efforts to areas and groups that need it most in order to achieve the highest impact.

Completion of this ARCC-funded study will now allow us to proceed to a) design a pragmatic cluster randomized de-implementation trial to test our multifaceted, geographically tailored intervention and b) perform an economic analysis of the cost of this inappropriate non-evidence based practice currently; the cost savings after the de-implementation intervention; and the cost of the de-implementation strategy.

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