[Ponderal evolution in the Girona population, 1989-1999]

Breast cancer incidence and overdiagnosis in Catalonia (Spain)

Introduction

Early detection of breast cancer (BC) with mammography may cause overdiagnosis and overtreatment, detecting tumors which would remain undiagnosed during a lifetime. The aims of this study were: first, to model invasive BC incidence trends in Catalonia (Spain) taking into account reproductive and screening data; and second, to quantify the extent of BC overdiagnosis.

Methods

We modeled the incidence of invasive BC using a Poisson regression model. Explanatory variables were: age at diagnosis and cohort characteristics (completed fertility rate, percentage of women that use mammography at age 50, and year of birth). This model also was used to estimate the background incidence in the absence of screening. We used a probabilistic model to estimate the expected BC incidence if women in the population used mammography as reported in health surveys. The difference between the observed and expected cumulative incidences provided an estimate of overdiagnosis.

Results

Incidence of invasive BC increased, especially in cohorts born from 1940 to 1955. The biggest increase was observed in these cohorts between the ages of 50 to 65 years, where the final BC incidence rates more than doubled the initial ones. Dissemination of mammography was significantly associated with BC incidence and overdiagnosis. Our estimates of overdiagnosis ranged from 0.4% to 46.6%, for women born around 1935 and 1950, respectively.

Conclusions

Our results support the existence of overdiagnosis in Catalonia attributed to mammography usage, and the limited malignant potential of some tumors may play an important role. Women should be better informed about this risk. Research should be oriented towards personalized screening and risk assessment tools.

[Time trend of breast cancer incidence in Catalonia]

BACKGROUND AND OBJECTIVE

Time trend of breast cancer incidence in Catalonia in the last 20 years is evaluated by a age-period-cohort model.

POPULATION AND METHOD

Women older than 25 years diagnosed with breast cancer between 1980 and 1999 in the population covered by Tarragona and Girona population-based cancer registries. To investigate the age, period and birth cohort effect in the time trends of breast cancer incidence, Decarli and La Vecchia and Holdford's methods were used.

RESULTS

The world age-standardized rate (25 to > or = 85 years old) has increased from 53.9 cases per 100,000 women-year in the period 1980-1984 to 83.9 per 100,000 women-year in the period 1995-1999. The annual percentage change was 2.2% (95% confidence interval, 1.8-2.6). According to age-period-cohort model an increment of the incidence exists depending on age and birth cohort, being the period effect less important.

CONCLUSIONS

Breast cancer incidence has significantly increased in Catalonia. The birth cohort seems to be more important than the period effect in this increment, which supposes a change on the prevalence of the risk factor, although the use of screening diagnosis techniques might explain a part of the period effect.