Improved prognosis of breast cancer since 1970 in south-eastern Netherlands

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Abstract
Despite many new advances in breast cancer therapy since the 1970s, there are only few reports on improved prognosis in a general population. A follow-up of more than 10 years is rarely reported, and a differentiation according to stage of the disease or between follow-up intervals is seldom made. Our purpose was to assess whether prognosis of primary breast cancer improved in patients diagnosed between 1970 and 1984 in south-eastern Netherlands, and to distinguish between different stages and follow-up intervals. Data from 4,467 breast cancer patients diagnosed between 1970 and 1984 were derived from the population-based Eindhoven Cancer Registry. Follow-up was attained up to 1 July 1991. Relative survival rates, as the ratio of the observed to the expected rates, were calculated. In a multivariate analysis a change in prognosis over time was computed with adjustment for age and stage; this was done separately for 5 year follow-up intervals. The relative survival rates were 69% after 5 years, 55% after 10 years and 50% after 20 years. Relative survival, after adjustment for age, was strongly related to the stage of the disease in the first 5 years of follow-up, less markedly between 5 and 10 years, and to a small, borderline significant, extent after 10 years of follow-up. Relative survival rates increased markedly over time, during the whole interval of follow-up. This increase was apparent in all age groups and in all stages, except for those with distant disease at diagnosis. The observed improvement in survival is unlikely to be explained by the increased use of adjuvant chemo- and hormonal therapy. Other factors, such as a change in the natural history of the disease in this period, cannot be ruled out.