Francis P. Boscoe, Ph.D, Research Scientist, New York State Cancer Registry (NAACCR at-large Board Member)
This week, a team of researchers published a study using central cancer registry data which found that U.S. counties where 40% of the women met mammography screening guidelines in 2000 had age-adjusted incidence rates of about 200 per 100,000 and ten-year mortality rates of about 50 per 100,000. Counties where 80% of the women met mammography screening guidelines in 2000 (twice as many) had age-adjusted incidence rates of about 350 per 100,000 (almost twice as many) and ten-year mortality rates of about 50 per 100,000 (exactly the same). While they took this as further evidence against the unqualified utility of mammography, they were careful not to overstate the point. Instead, they helpfully concluded:
“As is the case with screening in general, the balance of benefits and harms is likely to be most favorable when screening is directed to those at high risk, provided neither too frequently nor too rarely, and sometimes followed by watchful waiting instead of immediate active treatment”.
Given the very different risk profiles associated with breast cancer subtypes, might we be moving toward a time when screening recommendations are based on more than just age?
Here is an editorial follow-up to this article by one of its authors, published in the Los Angeles Times.
“If you haven’t gotten this message already, you should heed it now: The benefits of screening for breast cancer are limited. We should be doing fewer screening mammograms, not more.” …
Read Full Article (The abstract below is from an article from JAMA Internal Medicine)
Abstract
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Importance: Screening mammography rates vary considerably by location in the United States, providing a natural opportunity to investigate the associations of screening with breast cancer incidence and mortality, which are subjects of debate.
Objective: To examine the associations between rates of modern screening mammography and the incidence of breast cancer, mortality from breast cancer, and tumor size.
Design, Setting, and Participants: An ecological study of 16 million women 40 years or older who resided in 547 counties reporting to the Surveillance, Epidemiology, and End Results cancer registries during the year 2000. Of these women, 53 207 were diagnosed with breast cancer that year and followed up for the next 10 years. The study covered the period January 1, 2000, to December 31, 2010, and the analysis was performed between April 2013 and March 2015.
Exposures: Extent of screening in each county, assessed as the percentage of included women who received a screening mammogram in the prior 2 years.
Main Outcomes and Measures: Breast cancer incidence in 2000 and incidence-based breast cancer mortality during the 10-year follow-up. Incidence and mortality were calculated for each county and age adjusted to the US population.
Results: Across US counties, there was a positive correlation between the extent of screening and breast cancer incidence (weighted r = 0.54; P < .001) but not with breast cancer mortality (weighted r = 0.00; P = .98). An absolute increase of 10 percentage points in the extent of screening was accompanied by 16% more breast cancer diagnoses (relative rate [RR], 1.16; 95% CI, 1.13-1.19) but no significant change in breast cancer deaths (RR, 1.01; 95% CI, 0.96-1.06). In an analysis stratified by tumor size, we found that more screening was strongly associated with an increased incidence of small breast cancers (≤2 cm) but not with a decreased incidence of larger breast cancers (>2 cm). An increase of 10 percentage points in screening was associated with a 25% increase in the incidence of small breast cancers (RR, 1.25; 95% CI, 1.18-1.32) and a 7% increase in the incidence of larger breast cancers (RR, 1.07; 95% CI, 1.02-1.12).
Conclusions and Relevance: When analyzed at the county level, the clearest result of mammography screening is the diagnosis of additional small cancers. Furthermore, there is no concomitant decline in the detection of larger cancers, which might explain the absence of any significant difference in the overall rate of death from the disease. Together, these findings suggest widespread overdiagnosis.
The opinions expressed in this article are those of the authors and may not represent the official positions of NAACCR.
