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Original Investigation | Less Is More

Breast Cancer Screening, Incidence, and Mortality Across US Counties

Charles Harding, AB1; Francesco Pompei, PhD2; Dmitriy Burmistrov, PhD2; H. Gilbert Welch, MD, MPH3; Rediet Abebe, MASt4; Richard Wilson, DPhil2
[+] Author Affiliations
1Currently in private practice, Seattle, Washington
2Department of Physics, Harvard University, Cambridge, Massachusetts
3Department of Medicine, The Dartmouth Institute for Health Policy and Clinical Practice, Hanover, New Hampshire
4Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts
JAMA Intern Med. 2015;175(9):1483-1489. doi:10.1001/jamainternmed.2015.3043.
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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.

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Figure 1.
Patient Selection and Exclusion

AJCC indicates American Joint Commission on Cancer; SEER, Surveillance, Epidemiology, and End Results.

aPaget disease of the nipple without underlying tumor.

bInflammatory carcinoma (International Classification of Diseases for Oncology, 3rd edition, code 8530/3), diffuse, widespread—three-fourths or more of breast.

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Figure 2.
Extent of Screening, Breast Cancer Incidence, and Mortality From Breast Cancer Among Women 40 Years and Older in 547 US Counties

Each circle presents data for a single county; circle area is proportional to the county population of women 40 years and older. Each fitted curve is a smoothing spline, presented with 95% confidence bands.

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Figure 3.
Extent of Screening and Breast Cancer Incidence, Stratified by Tumor Size

A, Tumors ≤2 cm. B, Tumors >2 cm. Each circle presents data for a single county; circle area is proportional to the county’s population of women 40 years and older. Each fitted curve is a smoothing spline, presented with 95% confidence bands.

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Figure 4.
Extent of Screening and Breast Cancer Incidence, Stratified by Stage and First-Course Surgical Treatment

A, Early disease indicates American Joint Commission on Cancer, 6th edition, stages 0-II and locally advanced and metastatic disease indicates American Joint Commission on Cancer, 6th edition, stages III-IV. We judged that locally advanced and metastatic disease is unambiguously progressive, in that overdiagnosed indolent disease would be unlikely among these cases, even if there were false-positive hormone status, lymph node involvement, or other test results. B, Breast-conserving indicates excisional biopsy, re-excision of biopsy site, lumpectomy, partial mastectomy, and segmental mastectomy. Non–breast-conserving indicates total or simple mastectomy, radical mastectomy, modified radical mastectomy, and subcutaneous mastectomy.

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Age and Screening
Posted on August 3, 2015
Rabeb Khlifi
CRCHUM, Université de Montréal (UdeM), Montreal, Quebec,Canada
Conflict of Interest: None Declared
This is a very interesting study examining the association between the mammography screening rates at the county level and breast cancer incidence and mortality. Given the considerably controversy surrounding the optimal age at which women should be screened, it would be interesting to present separately the analysis for women 50 and over and those under 50 years of age.
Suppose Another Conclusion is Possible?
Posted on October 14, 2015
Marybeth Lambe MD FAAFP
Watergrass Hill
Conflict of Interest: None Declared
This will sound rash & foolish in contrast with this brilliant and rather heroic research, but I am holding out hope to know further imagined data. Especially since this has set off such a boisterous clamor against screening mammograms in my community. Previous discussion has touched overtreatment but always centered around false positives & harm vs benefit so this was hugely surprising. I am just a lowly local physician, yet I was thinking of how carefully I send women for screening & just to whom & where I send them. I wondered if there was any chance this lovely analysis could be dissected down very small. If tiny subsets could be pulled out & examined—is there any chance to look at centers of excellence to know, well, if excellence matters in this? Are we still left with the uncomfortable truth of no correlation between screening and breast cancer mortality change?

In my practice & then in reading the research, I worry about who is reading the mammogram, or who then the ultrasound, how very experienced will be the patient’s cautious, wise breast specialist next. Even here in Seattle, I use much caution--many sites, many readers, many surgeons would be hopeless and overcall, over biopsy—so I never send them there. Multiple this by a million...
Is there any way of parceling out the data gathered & sorting it by excellence of the mammogram site, mammogram reader, sagacity of breast specialists used ? Would that alter the data; worse—would it not?

Frankly, the inequity, the unevenness of health care, of health prevention, in this country is appalling & quite well known. I know this research appears in a series of “Less is More” but I am old & I was taught to always first brainstorm all the possible diagnoses. Sometimes, there is more before we can clinch the case as less. Would we find instead a need for cloning the very few GOOD mammogram centers, the thoughtful mammogram radiology readers, the cautious breast surgeons, & caring referral people? Or worse, still to be wrong—for all the best & attentive specialists to make no difference. What I wonder, if the data could be pulled apart like that, the large US cohort, whirled down to small intersections; likely impossible. But, oh the value of knowing would make all the difference! Does great care alter these results?
Should the epilogue be instead? Be Careful Where, & with Whom, You Trust Your Breasts
increased screening=increased detection
Posted on December 27, 2015
leong
private practice, former prof dartmouth
Conflict of Interest: None Declared
as expected, the study showed that increased screening results in increased incidence of breast cancer detection, particularly small cancer. unfortunately, the study was retrospective and was not specific regarding how frequently these patients were screened, other than to state that screening was done within 2 years. to claim that increased screening results in over diagnosis is a stretch unless there is a vertical study or prospective study where all patients are followed long term. since this is cross sectional study, it is expected that each year, new cancer diagnoses will occur with fewer large cancers than small. a yearly cross section for 10 years may not be enough to tease out any effect screening has on the diagnosis of larger cancers since the screening rate is not 100% and the population is not stable.
breast cancer mortality rates are due to a number of factors, of which size of tumor at time of diagnosis is only a part of the equation. tumor biology and receptor status plays a very important role and is not detectable via screening.
the study does raise interesting issues about the utility of screening mammography in mortality, but until we can obtain 100% screening rates, we cannot be certain that it is not effective.
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