I know most of you may not be reading this email on Friday because it’s the Fourth of July. I’ll try to send it out earlier or you might pick it up after the holiday. So Happy 4th and enjoy the barbecue, parades and fireworks.
I couldn’t let the week go by without reporting on an article in the June 25 issue of JAMA that reports on a study of breast cancer screening using a method called tomosynthesis. The efficacy of tomosynthesis combined with digital mammogram was compared to digital mammogram only for breast cancer screening. A debate about the utility of digital mammogram has once more been brought up by the recent publication of the 25 year follow-up results from the Canadian National Breast Screening Study. It showed that there was no difference in breast cancer-related mortality in screened women versus controls. Many physicians and organizations have however, countered that these results were not valid for current U.S.policy; that the study was based on mammograms that were of poor image quality and that there were significant problems in randomization. Indeed, 14 more recent studies published between 2001 and 2010 have indeed shown a 25 to 50% reduction in breast cancer related mortality for women aged 42 to 74 years who had modern (and presumably better) types of digital mammogram screening. The American Cancer Society, the American Congress of Obstetricians and Gynecologists and other organizations still recommend screening mammography annually for women older than 40 years. The American Cancer Society also recommends annual MRI for women with a 20 to 25% or higher lifetime risk of breast cancer.
The article in JAMA is a retrospective analysis of screening in 13 centers over two time periods. During the initial period more than 281,000 examinations were done with digital mammogram alone. The second period included more than 173,000 examinations during which patients underwent combined digital mammogram and tomosynthesis screening. I know the word “tomosynthesis” sounds very synthetic biology. It is high tech but but not a biological creation. Basically, it is composed of a set of low-dose images produced by x-rays as they moves across the breast. The images are then put together to form a picture by a computer algorithm (of course) that reconstructs the images as slices of the breast. The advantage is in the resolution and clarity of the final image. An area may look suspicious because tissue overlaps from the pressure of a simple mammogram procedure; tomosynthesis is meant to prevent this effect and hence reduce false densities while making a cancer appear more conspicuous.
So does adding tomosynthesis to usual breast screening make a clinical difference? In this study the authors found that the introduction of tomosynthesis was associated with a significant decrease in recall rate (i.e the. need to get additional films, ultrasound, MRI or even biopsy) of 1.6%. There was however, a significant increase in the biopsy rate (1.3%), but perhaps the biopsies were more likely to confirm a cancer. There was an increase in the cancer detection rate of 0.12%. The latter doesn’t sound like much, but it made a difference for the 1.2 women whose cancer was found per 1000 screenings… They might not have had that early diagnosis with standard mammograms. There is however, as always, a drawback in medical innovation and the one here is that tomosynthesis requires twice as much radiation as a regular digital mammogram. And it is too early to know if adding this procedure will impact mortality rates from breast cancer.
In an editorial in the same journal the authors state that “Recent work has suggested that tomosynthesis is likely to outperform mammogram in finding small invasive cancers and lobular cancers, the ones that are most likely to be lethal.”
This and other studies raise some major questions for both physicians and women. Should we seek screening with tomosynthesis over digital mammogram? Should breast cancer screening centers convert to tomosynthesis and abandoned digital mammography? (Which will be costly.) Right now there doesn’t seem to be enough data or financial incentive to do so. But, tomosynthesis may indeed be an advance over digital mammogram for breast cancer screening and one day may become the norm in breast screening. As usual, I’ll end with the off-stated refrain…More studies are needed.