Friday, October 24, 2014

Comment on Breast Cancer in Science

I’ve just had a small comment on breast cancer published on Science’s website. The comment is in reply to an interesting article discussing over-treatment in ductal carcinoma in situ (DCIS: a type of cancer that is contained in the milk duct). My comment is reprinted below. Unfortunately Science’s website submission system mucked up some of the letter (formatting etc.) but no matter as it can be read here:

Finding biomarkers in DCIS and the effects of breast cancer screening

Marshall’s article [1] raised the important issue of overtreatment in breast cancer. It is challenging to assess which ductal carcinomas in situ (DCIS) are overtreated without risking a patient’s life. The studies being conducted by Esserman and colleagues are an important step in addressing this problem. Such studies could assist in the identification of biomarkers (blood tests, MRI, etc.) that can separate those types of DCIS that will proceed to a life threatening stage from those that are indolent. MRI has assisted in breast cancer detection and characterization with a high level of sensitivity and the additional tumours detected have generally not been accompanied by a change in the way such tumours are treated. Multifocal cancer is often treated with mastectomy which is likely to be an excessive treatment option in some cases where small multifocal DCIS lesions are detected by MRI.

The article also comments on the lack of a drop in advanced stage tumours at a population level after an increase in mammographic use [1]. Randomized controlled trials do report reductions in the rate of advanced stage tumours in those who receive mammography [2]. At the population level we are not monitoring who receives mammography and who does not. Brody et al. [3] have raised a potentially relevant point that environmental carcinogens are likely to be contributing to an increase in breast cancer rates. Older subjects will have been exposed to environmental carcinogens for a longer period of time and as such should exhibit higher rates of cancer. Since it is well known that breast cancer rates increase with age, we should consider the possibility that environmental carcinogens are a contributing factor to this effect. If true, then a stable rate of late stage cancers in an environment where the rate should be increasing would be an indication that mammography has indeed lowered the rate from what it would otherwise be. The rate of advanced stage cancer [1] would thus consist of lower rates for those receiving mammography and higher rates for those who are not.

Jacob Levman, PhD
University of Oxford

[1] Marshall, Dare to Do Less, Science, (2014)343(6178):1454-1456
[2] Marmot, et al., The benefits and harms of breast cancer screening: an independent review, British Journal of Cancer, (2013)108:2205-2240
[3] Brody, et al., Breast Cancer and Environmental Research, Science, (2014)344(6184):577