Comparing interval breast cancer rates in Norway and North Carolina: results and challenges.
OBJECTIVE
To compare interval breast cancer rates (ICR) between a biennial organized screening programme in Norway and annual opportunistic screening in North Carolina (NC) for different conceptualizations of interval cancer.


METHODS
Two regions with different screening practices and performance.


METHODS
620,145 subsequent screens (1996-2002) performed in women aged 50-69 and 1280 interval cancers were analysed. Various definitions and quantification methods for interval cancers were compared.


RESULTS
ICR for one year follow-up were lower in Norway compared with NC both when the rate was based on all screens (0.54 versus 1.29 per 1000 screens), negative final assessments (0.54 versus 1.29 per 1000 screens), and negative screening assessments (0.53 versus 1.28 per 1000 screens). The rate of ductal carcinoma in situ was significantly lower in Norway than in NC for cases diagnosed in both the first and second year after screening. The distributions of histopathological tumour size and lymph node involvement in invasive cases did not differ between the two regions for interval cancers diagnosed during the first year after screening. In contrast, in the second year after screening, tumour characteristics remained stable in Norway but became prognostically more favorable in NC.


CONCLUSIONS
Even when applying a common set of definitions of interval cancer, the ICR was lower in Norway than in NC. Different definitions of interval cancer did not influence the ICR within Norway or NC. Organization of screening and screening performance might be major contributors to the differences in ICR between Norway and NC.
Hofvind
Solveig
S
Department of Screening Based-research, The Cancer Registry of Norway, Oslo, Norway. solveig.hofvind@kreftregisteret.no
Yankaskas
Bonnie C
BC
Bulliard
Jean-Luc
JL
Klabunde
Carrie N
CN
Fracheboud
Jacques
J
D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008403:Mass Screening; D008875:Middle Aged; D009657:North Carolina / Q000453:epidemiology; D009664:Norway / Q000453:epidemiology