Estimate of overdiagnosis of breast cancer due to mammography after adjustment for lead time. A service screening study in Italy.
BACKGROUND
Excess of incidence rates is the expected consequence of service screening. The aim of this paper is to estimate the quota attributable to overdiagnosis in the breast cancer screening programmes in Northern and Central Italy.


METHODS
All patients with breast cancer diagnosed between 50 and 74 years who were resident in screening areas in the six years before and five years after the start of the screening programme were included. We calculated a corrected-for-lead-time number of observed cases for each calendar year. The number of observed incident cases was reduced by the number of screen-detected cases in that year and incremented by the estimated number of screen-detected cases that would have arisen clinically in that year.


RESULTS
In total we included 13,519 and 13,999 breast cancer cases diagnosed in the pre-screening and screening years, respectively. In total, the excess ratio of observed to predicted in situ and invasive cases was 36.2%. After correction for lead time the excess ratio was 4.6% (95% confidence interval 2 to 7%) and for invasive cases only it was 3.2% (95% confidence interval 1 to 6%).


CONCLUSIONS
The remaining excess of cancers after individual correction for lead time was lower than 5%.
Paci
Eugenio
E
Clinical and Descriptive Epidemiology Unit, CSPO, Research Institute of the Tuscany Region, via di San Salvi 12, Firenze, 50135, Italy. e.paci@cspo.it
Miccinesi
Guido
G
Puliti
Donella
D
Baldazzi
Paola
P
De Lisi
Vincenzo
V
Falcini
Fabio
F
Cirilli
Claudia
C
Ferretti
Stefano
S
Mangone
Lucia
L
Finarelli
Alba Carola
AC
Rosso
Stefano
S
Segnan
Nereo
N
Stracci
Fabrizio
F
Traina
Adele
A
Tumino
Rosario
R
Zorzi
Manuel
M
D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D007558:Italy / Q000453:epidemiology; D008327:Mammography; D008403:Mass Screening; D008875:Middle Aged; D013997:Time Factors