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Does detection and treatment of ductal carcinoma in situ prevent invasive cancer?

664 Background: The diagnostic incidence of ductal carcinoma in situ (DCIS) has increased over 500-fold in the last 3 decades. It is not clear whether detection and treatment of DCIS prevents development of invasive breast cancer (IBC).


METHODS
We identified all cases of DCIS (n = 1,157) and IBC (n = 9,072) in Monroe County, NY from 1985 - 2002 using the Monroe County Tumor Registry. We linearly extrapolated and interpolated zip code level population totals for women age 35 -79 by year from 1990 and 2000 census data. We then generated incidence rates for DCIS and IBC by zip code and year from 1985 - 2002. To investigate the impact of DCIS detection on IBC incidence, we estimated regression models in which IBC rates were specified as flexible functions of time and lagged DCIS rates. We allowed for IBC rates to be affected by lagged DCIS rates (each of the five prior years) because of the possibility that transit time from in situ to invasive disease is heterogeneous. We included zip code-level fixed effects to eliminate spurious correlation due to unobservable zip code factors that may drive both DCIS and invasive cancer rates. Thus, the relationship between invasive cancer and lagged DCIS is identified by intra-zip code variations in DCIS and invasive cancer rates over time.


RESULTS
Bivariate analysis shows that DCIS and IBC rates are positively correlated. Multivariate results, however, indicate that there is a strong negative relationship between lagged DCIS diagnosis rates and IBC rates. The model predicts that 33% (p = .014) of diagnosed DCIS cases would have been diagnosed as IBC cases in two years, a total of almost 50% (p = .06) in the first three years combined, and a total of 72% (p = .046) in the first 5 years combined. The sum of the effects of lagged DCIS rates from years 1 through 5 is significantly different from 0 (p = .046). The relationships become stronger when socioeconomic and demographic controls are included in the model.


CONCLUSIONS
Results indicate that DCIS diagnoses reduce future IBC diagnoses. This suggests that the natural history of DCIS is progression to IBC at high rates within two to five years. Our results underscore the importance of screening for, detection of, and treatment of DCIS. [Table: see text].