November 26, 2012

Screening Mammography Overdiagnoses Breast Cancer?

The recently published NEJM's original article describes effect of screening mammography on breast cancer incidence in the USA. Bleyer A and Welch HG. N Eng J Med 2012;367:1998 (22 Nov 2012)

Facts: Aim of Cancer Screening

  • We expect cancer screening program to lower cancer-related mortality by a means of 1) earlier detection of disease destined to be fatal and 2) early Rx of screen-detected cancers
  • A cancer screening program should 1) increase incidence of cancer detected at an earlier stage and 2) decrease incidence of cancer presenting at a late stage

What Study Is About And What It Has Found:
  • Breast cancer rate from 1976 through 1978 (mammography was uncommon) ~ baseline incidence
  • Breast cancer rate from 2006 through 2008 ~ current incidence
  • Confounding effects of menopausal hormone therapy were minimized by not including transitory increase in incident breast cancers from 1990 through 2005. Underlying incidence of breast cancer assumed to rise by 0.25% annually
  • Number of cases of early-staged breast cancer rises from 112 to 234 cases per 100,000 women
  • Number of cases of late-staged breast cancer decreases from 102 to 94 cases per 100,000 women
  • "With an assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease." This was estimated that breast cancer was overdiagnosed. In 2008, the overdiagnosis would account for 31% of all breast cancer diagnosed
Other Studies Said?
Results of this study concur with other reports (references 2-3) and suggest that improvements in treatment are the main drive in reducing breast cancer mortality - rather than screening mammography. 

It is suggested that "pros and cons of mammography should be incorporated into the counseling that women receive as they decide whether an when to be screened". 

  1. Bleyer A and Welch HG. Effect of three decades of screening mammography on breast cancer incidence. N Eng J Med 2012;367:1998
  2. Kalager M et al. Effect of screening mammography on breast cancer mortality in Norway. N Eng J Med 2010;363:1203
  3. Autier P et al. Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: trend analysis of WHO mortality database. BMJ 2011;343:d4411
  4. Kaunitz AM. Screening mammography: does overdiagnosis overshadow prevention of advanced breast cancer? Journal Watch Women's Health November 21, 2012

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