Screening Mammography Has Little Impact on Advanced Cancer Rates

Fran Lowry

December 08, 2017

Screening mammography over a period of 24 years among women age 50 to 74 years has had little effect on reducing rates of advanced breast cancer or mortality from breast cancer in the Netherlands, according to new research.

Screening did, however, dramatically increase the detection of early-stage breast cancer, both ductal carcinoma in situ (DCIS) and stage I and, in so doing, contributed to increased rates of overdiagnosis — defined as detection of tumors on screening that would never lead to clinical symptoms in a woman's lifetime.

The study, published in the BMJ, concludes that screening would be associated with zero to 5% reductions in breast cancer mortality in women aged 50 years and older, whereas improved treatments would be associated with a 28% reduction in mortality.

Additionally, screening mammography was associated with a 32% increase in overdiagnosis, an increase driven by the advent of digital mammography and the extension of screening to women aged 70 to 75 years, the authors write.

"The main purpose of cancer screening is to catch the cancer at an early stage before it becomes metastatic disease," lead author, Philippe Autier, MD, from University of Strathclyde Institute of Global Public Health, Lyon, France, told Medscape Medical News.

Dr Philippe Autier

"If screening works, then you must observe a decreased incidence in the burden of advanced, poor-prognosis cancer in the population. While we have seen decreases in the incidence rate of advanced cervical and colorectal cancer, the same thing has not been true for breast cancer," Dr Autier said.

"Everybody was expecting, myself included, that the same would be true for mammography screening, but unfortunately, after years and years of screening, we are realizing that we are not seeing reductions in advanced breast cancer. This is something that is being observed not just in the Netherlands but in all countries where there is a lot of screening, including the United States," he said.

Results From the Netherlands  

Since 1989, women age 50 to 69 in the Netherlands have been invited to have a screening mammogram every 2 years. In 1997, screening was extended to include women age 70 to 75 years.

Digital mammography became available in the Netherlands in 2006.

Dr Autier and his group studied trends in stage-specific age-adjusted incidence of breast cancer among women participating in the Netherlands national breast screening program from 1989 to 2012.

They found that the incidence of stage II to IV breast cancers in women aged 50 years or older was 168 per 100,000 in 1989 and 166 per 100,000 in 2012.

They also found that, after deducting of clinical lead time cancers, 32% of cancers found in women who were screened in 2010 to 2012 were overdiagnosed, and also that 59% of screen-detected cancers would be overdiagnosed.

Women aged 70 to 74 were particularly prone to overdiagnosis. In that age group, the overdiagnosis of stage I cancers was about two times higher than in women aged 50 to 69.

"These observations are in line with other data showing that the replacement of film-based mammography by digital mammography has substantially increased the burden of in situ breast tumors without decreasing rates of interval cancers," Dr Autier said.

"It strongly suggests that the advent of digital technologies has probably worsened the overdiagnosis problem without clear evidence for improvements in the ability of screening to curb the risk of breast cancer death," he said.

A Radiologist's Take

Approached for a reaction to the new findings from the Netherlands,

Stamatia Destounis, MD, clinical professor, Rochester University School of Medicine, New York, told Medscape Medical News: "I think they are misinterpreting their data."

Dr Stamatia Destounis

"They are making assumptions here that are not supported. For instance, the rate of invasive cancers before screening mammography had been increasing, so the fact that this rate remained stable during the period of the study actually represents a decrease and proves that there is a benefit for screening," Dr Destounis said.

Dr Destounis also takes issue with combining DCIS and stage I breast cancer as one entity, which she says confounds the issue of overdiagnosis.

 "There are some legitimate issues with DCIS with regard to overdiagnosis, but to combine the two [DCIS and stage I] complicates their analysis. The benefit of screening, whether it's for breast, or colon, or any body part is to find the small invasive cancer so that it does not become stage II," she said.

While some in situ cancers may be indolent and may not develop into an invasive cancer, there is currently no way of knowing which ones they are, Dr Destounis said.

"Our job as radiologists is to detect every new abnormality, and that is what mammography screening is very good at doing. There may be room to change our position after the pathologist interprets the screen as being very early low-grade DCIS, and I think there are changes occurring right now in the US with regard to what to do about those very early in situ tumors, but the authors have done a disservice by lumping DCIS and stage I together," she said.

"The way these authors analyzed their data is faulty. The point of screening mammography is to find those stage I cancers and obviously we are doing a good job at doing that. Even their own analysis shows that we are doing a good job finding these stage I tumors, and in all age groups," she added.

Calls Benefits of Screening Into Question

However, an expert in public health who has raised questions about the benefits of regular mammography screenings for many women says the new results from the Netherlands affirm other findings.

"This study in the Netherlands basically replicates the picture in the United States," H. Gilbert Welch, MD, MPH, professor of medicine, Dartmouth Institute for Health Policy & Clinical Practice, Lebanon, New Hampshire, told  Medscape Medical News.

Dr H. Gilbert Welch

"The widespread introduction of mammography is associated with a dramatic increase in the detection of early-stage breast cancer but little concomitant decline in the rate at which women present with late-stage breast cancer. This combination suggests that screening mammography has little effect on breast cancer mortality, and that the decline in mortality that we have seen in the last 20 years or so is largely the result of better treatment," Dr Welch commented.

Dr Welch coauthored a 2012 study with Archie Bleyer, MD, Oregon Health and Science University, Portland, which showed similar results, including a 30% increase in rates of overdiagnosis and only a small effect on the rate of death from breast cancer. That study was published in the New England Journal of Medicine .

"An important message is that you don't solve the problem by throwing more technology at it. Adding an ultrasound, adding an MRI, adding digital mammography, this only makes the problem of overdiagnosis worse. The harder you look for this stuff, the more likely you are going to get into the overdiagnosis problem," Dr Welch said.

"We have been pushing screening mammography too much. We've totally overstated its benefits and understated its harms. It can lead a woman to be treated for breast cancer who otherwise would never need to know about it," he said.

Older individuals in particular should be wary of undergoing cancer screening, he said.

"When you start getting older, you don't want to be doing any kind of cancer screening. It creates more problems than it solves. It leads to a lot more procedures, you end up getting medicalized, and some people have surgery. Urologists agreed very early on that people with limited life expectancy should not be screened for prostate cancer [as] only bad things can happen as a result of that. I think the general story is we've gone a little overboard in our desire to find cancer early," Dr Welch said.

"Women aged 70 to 75 are the ones who really have a shoot-up in incidence when they start screening. Most of the cancers that are found are not relevant and for those that are, most can be treated. I know it's a counterculture message, but I think it's the truth," he said.

Breast cancer mortality is falling, not because of screening but because treatments have improved, Dr Welch said.

"That's the good news that a lot of people miss. We are much better at treating breast cancer than we were 20 years ago. Ironically, the better we become at treating breast cancer, the less important screening becomes," he added.

The study was supported by the International Prevention Research Institute. Dr Autier, Dr Welch, and Dr. Destounis have disclosed no relevant financial relationships.

BMJ  2017;359:j5224. Full text

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