From Capital Region Action Against Breast Cancer! (CRAAB!):
by Jessica Werder, M.P.H.
Background and Recent Evidence:
The Canadian National Breast Screening Study was initiated in 1980 to explore two questions: (1) was there a benefit of screening mammography when added to “usual care” among women aged 40 – 49; (2) did adding mammography screening to regular (clinical) breast examination make any difference for women aged 50 – 59? Overall, the study was designed to look for benefits (or hazards) of adding regular mammograms to high quality healthcare.
The study was designed as a large, randomized controlled trial, with a total of 89,835 women enrolled between the ages of 40 and 59. Younger women, ages 40 to 49, were randomly assigned to receive either mammography or no mammography. All were given good breast healthcare and taught breast self-exams. Older women, ages 50 – 59, were blindly assigned to receive mammography or no mammography. All received Clinical Breast Exams from trained professionals.
Initial reports after a decade of follow up showed no mortality benefit from adding mammograms to good breast healthcare for either age group. This unexpected result differed from other studies claiming benefits as high as 35% or morev, and it challenged the widely held belief that mammography screening saves lives by finding cancer “early.”
The most recent paper reports follow-up after 25 years of combined data for all women studied, ages 40 – 59, updating survival and mortality rates. In light of more recent understanding of different types of breast cancer along with the mammographic detection of smaller micro-tumors, the researchers also examined tumor characteristics in those women who developed breast cancer. vi
After analysis, they once again found no statistical difference in the rate of death between women who had a mammogram and those that did not but had good healthcare. They concluded that “Annual mammography in women aged 40-59 does not reduce mortality from breast cancer beyond that of physical examination or usual care when adjuvant therapy for breast cancer is freely available.” In addition, they found that 22% of invasive cancers diagnosed via mammography screening were “overdiagnosed,” meaning that the cancer, while detected, would not have led to any clinically significant disease in a woman’s lifetime.
Interpretations and Implications
There has been a lot of attention in recent years paid to mammography and the question of whether it provides clinical benefit above and beyond regular care and physical examinations. Based on mounting evidence that mammography confers little advantage in survival, and that it often leads to false positives, the U.S. Preventive Services Task Force (USPSTF) changed its screening recommendations in 2009 to suggest screening for women begin at age 50, instead of its previous recommendation of age 40.viii USPSTF 2009 also concluded it would not recommend mammogram screening for women over 74 because not enough evidence pointed to benefits for that age group, while much new evidence revealed mammography’s increased risk for overtreatment. It also advised skipping every other year to get the same results with half the radiation exposure. This most recent Canadian study evidence adds support to this change and provides more data for the conversation about mammography as a routine screening procedure.
More recent information goes beyond the problem of false positives and excessive biopsies to actual “overdiagnosis and overtreatment.” The problem becomes that mammography leads to detection of cancers that do not become disease problems in our lifetimes. The original 2000 report showed 30% more surgeries and adjuvant treatments in the mammography group—with no mortality benefit. The updated information distinguishes between invasive cancers and localized ones like DCIS, showing 1 in 5 women diagnosed with invasive breast cancer did not have to be treated at all. The terrible challenge we face now is how to distinguish those cancers that can be ignored and those that will progress to disease.
Excerpt from the CRAAB Newsletter Winter-Spring2014.pdf
i Wu Q et al. 27-Hydroxycholesterol Promotes Cell-Autonomous, ER-Positive Breast Cancer Growth. Cell Reports 2013, 14;5(3):637-4. ii Azrad M1 et al. The association between adiposity and breast cancer recurrence and survival: a review of the recent literature. Current Nutrition Reports 2014, 3(1):9-15. iii Chyou PH et al. Prospective study of serum cholesterol and site-specific cancers. Journal of Clinical Epidemiology 1992, 45:287–92. iv Hubalek M. Does Obesity Interfere With Anastrozole Treatment? Positive Association Between Body Mass Index and Anastrozole Plasma Levels. Clinical Breast Cancer 2013, pii: S1526-8209(13)00313-3. doi: 10.1016/j.clbc.2013.12.008. [Epub ahead of print] v GØtzsche PC et al. Is screening for breast cancer with mammography justifiable? Lancet 2000, 355: 129-134. vi Miller AB et al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National BreastScreening Study: randomised screening trial. British Medical Journal 2014;348:g366. vii The Canadian study is not only strong in size and randomization (questioned but formally vindicated), it is the only study that compared mammography screening to good general and breast care. The other RCTs, which found up to 35% mortality benefits compared to 0% here, studied screening compared to doing nothing about breast health, which may well explain the different findings. In addition, among all the studies, this one is uniquely relevant today because it is the only one where modern protocols of adjuvant treatment were available. viii U.S. Preventive Services Task Force. “Screening for Breast Cancer.” November 2009.. http://www.uspreventiveservicestaskforce. org/uspstf/uspsbrca.htm. Accessed January 15 2014. ix Li Y et al. Circulating Proteolytic Products of Carboxypeptidase N for Early Detection of Breast Cancer. Clinical Chemistry 2014, 60(1):233-4.