I HAVE RECENTLY READ - Overdiagnosis more likely than early detection of threatening cancer

 

Overdiagnosis more likely than early detection of threatening cancer with mammography screening
Publish date: October 13, 2016

Author(s): Jessica Craig


Following the introduction of mammography, women were considerably more likely to have tumors that were overdiagnosed than to have earlier detection of a tumor that was destined to become large, according to an analysis of trends from the Surveillance, Epidemiology, and End Results (SEER) database.

To assess the effectiveness of screening mammography in the real-world clinical and community setting, H. Gilbert Welch, MD, of the Dartmouth Institute for Health Policy and Clinical Practice and his associates examined trends in breast tumor size between the years of 1975 and 2012, a span of time that can be broken down into two distinct periods: a baseline period that predated the widespread use of screening mammography (1975-1979) and a period encompassing the most recent years for which 10 years of follow-up data were available (2000 through 2002).

“Although the biologic characteristics of a tumor are now recognized to be more relevant to breast cancer prognosis than the size of the tumor, tumor size is more relevant to the assessment of the proximate effect of screening,” the researchers explained (N Engl J Med. 2016 Oct 12;375[15]:1438-47).

Retrospective analysis of the SEER database revealed a shift in the size distribution of breast tumors: Large tumors, defined as invasive tumors measuring two centimeters or more, predominated in the period before widespread screening mammography, and small tumors, defined as in situ carcinomas or invasive tumors measuring less than two centimeters, predominated after.

This shift, the researchers noted, can, in part, be attributed to the use of screening mammography.

Overall, from 1975 to 2012, the proportion of breast tumors that were small increased from 36% to 68%. In that same time period, the proportion of large tumors decreased from 64% to 32%.

“This shift in size distribution was less the result of a substantial decrease in the incidence of large tumors and more the result of substantial increases in the detection of small tumors,” Dr. Welch and his associates wrote.

Put another way, the incidence of small tumors increased by 162 cases of cancer per 100,000 women, from 82 to 244 cases, while the incidence of large tumors decreased by 30 cases of cancer per 100,000 women, from 145 to 115 cases. “Assuming that the underlying burden of clinically meaningful breast cancer was unchanged, these data suggest that 30 cases of cancer per 100,000 women were destined to become large but were detected earlier, and the remaining 132 cases of cancer per 100,000 women were overdiagnosed,” the researchers wrote.

“The magnitude of the imbalance indicates that women were considerably more likely to have tumors that were overdiagnosed than to have earlier detection of a tumor that was destined to become large,” the researchers continued. “Our analysis of size-specific incidence highlights the fact that the introduction of screening mammography has produced a mixture of effects,” Dr. Welch and his associates added.

     

 
     

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