We would like to thank Dr Gordon for her letter and the opportunity it provides for a response to the points she raises.

Her first two points relate to the potential of mammography screening to reduce surgical interventions through reduced rates of mastectomy and avoidance of axillary dissection. This seems likely to us, although the existence of screening-related overdiagnosis would indicate that, given current patterns of disease management, the overall rate of breast surgery will increase for participants in screening. In a study of BC data[1] we found that screening had only a modest effect on the use of breast-conserving surgery but a more pronounced effect on the avoidance of chemotherapy. 

Dr Gordon’s third point relates to the magnitude of breast cancer mortality reduction associated with screening. Again, we agree: several authors, including ourselves,[2] have found greater reductions in breast cancer mortality than were used in our results presented here. However, others have found less and this has been the topic of debate in the literature. We therefore elected to use rates that have been used by guideline groups in North America and the UK.[3-5] 

In her fourth point Dr Gordon indicates that overdiagnosis is not important unless it leads to overtreatment. We disagree. Once diagnosis occurs and is communicated, the “egg is broken” and a woman’s life is impacted. Future harm after diagnosis can be mitigated if it is possible to identify only the life-threatening cancers for treatment. The biggest hope would seem to be in development and use of molecular markers so that indolent disease is never diagnosed as cancer.

Finally, we share Dr Gordon’s enthusiasm for tomosynthesis and she is to be complimented for ensuring that this technology is being evaluated in BC. However, we would caution that increased cancer detection at screening, unless associated with reduction in the number of future cancers, does not guarantee a benefit. Future trials of this technology will be of great interest.
—Andrew Coldman, PhD
Vice President, Population Oncology, BCCA, and Adjunct Professor, Department of Statistics, UBC
—Norman Phillips, MSc
Senior Statistician, Cancer Surveillance and Outcomes, BCCA
—Christine Wilson, MD, FRCPC
Medical Director, Screening Mammography Program of BC, BCCA, and Clinical Associate Professor, Department of Medicine, UBC
—Janette Sam
Operations Director, Screening Mammography Program of BC

References

1.    Coldman AJ, Phillips N, Speers C. A retrospective study of the effect of participation in screening mammography on the use of chemotherapy and breast conserving surgery. Int J Cancer 2007;120:2185-2190.
2.    Coldman A, Phillips N, Warren L, et al. Breast cancer mortality after screening mammography in British Columbia women. Int J Cancer 2007;120:1076-1080.
3.    The Canadian Task Force on Preventive Health Care. Recommendations on screening for breast cancer in average-risk women aged 40-74 years. CMAJ 2011;183:1991-2001.
4.    US Preventive Services Task Force. Screening for breast cancer: U.S. Preventive Services Task Force recommendation statement. Ann Intern Med 2009;151:716-726. Errata in: Ann Intern Med 2010;152:199-200, Ann Intern Med 2010;152:688.
5.    Independent UK Panel on Breast Cancer Screening. The benefits and harms of breast cancer screening: An independent review. Lancet 2012;380:1778-1786.