Estimates of overdiagnosis of invasive breast cancer associated with screening mammography.
OBJECTIVE
To estimate the extent of overdiagnosis of invasive breast cancer associated with screening in New South Wales, Australia, a population with a well-established mammography screening program which has achieved full geographic coverage.


METHODS
We calculated overdiagnosis as the observed annual incidence of invasive breast cancer in NSW in 1999-2001 (a screened population) minus the expected annual incidence in this population at the same time, as a percentage of the expected incidence. We estimated expected incidence without screening in 1999-2001 from the incidence of invasive breast cancer in: (1) women in unscreened age groups (interpolation method); and (2) women in all age groups prior to the implementation of screening (extrapolation method). We then adjusted these estimates for trends in major risk factors for breast cancer that may have coincided with the introduction of mammography screening: increasing obesity, use of hormone replacement therapy (HRT) and nulliparity. Finally, we adjusted for lead time to produce estimates of expected incidence in 1999-2001. These were compared with the observed incidence in 1999-2001 to calculate overdiagnosis of breast cancer associated with screening.


RESULTS
Overdiagnosis of invasive breast cancer among 50-69 year NSW women was estimated to be 42 and 30% using the interpolation and extrapolation methods, respectively.


CONCLUSIONS
Overdiagnosis of invasive breast cancer attributable to mammography screening appears to be substantial. Our estimates are similar to recent estimates from other screening programmes. Overdiagnosis merits greater attention in research and in clinical and public health policy making.
Morrell
Stephen
S
School of Public Health, University of Sydney, Sydney, NSW, Australia. stephenm@health.usyd.edu.au
Barratt
Alexandra
A
Irwig
Les
L
Howard
Kirsten
K
Biesheuvel
Corné
C
Armstrong
Bruce
B
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000209:etiology; D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D005260:Female; D020249:Hormone Replacement Therapy / Q000009:adverse effects; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000592:standards*; D008403:Mass Screening / Q000592:standards*; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009517:New South Wales / Q000453:epidemiology; D009765:Obesity / Q000150:complications; D010298:Parity; D011247:Pregnancy; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity