Is breast cancer a curable disease? A study of 14,731 women with breast cancer from the Cancer Registry of Norway.

The question whether breast cancer is curable remains controversial. Late recurrences and death from the disease are not infrequent. Long term follow-up of a large patient population is necessary to study this issue. The authors report a study of 14,731 cases of breast cancer reported to the Cancer Registry of Norway with follow-up times ranging from 5 to 18 years. A model in which the logarithms of the survival times were assumed to be normally distributed, the lognormal model, fitted the data well for individual stages, age groups, and periods of treatment. The cured fraction, i.e., consisting of those only subject to normal mortality risks, was estimated from the model to 35 +/- 1% standard error. In Stages 1, 2, 3, and 4 it was 54 +/- 3%, 27 +/- 1%, 19 +/- 2%, and 2 +/- 1%, respectively. It is concluded, however, that the estimated cure rate in Stages 3 and 4 should be regarded with caution in view of the methodological problems involved in the analysis and the small number of patients with long follow-up. The estimated cured fraction in both the individual stages and in the entire material was significantly higher in patients younger than 55 years of age than in older patients. The median survival of non-cured patients was estimated to be 3.6 years for the entire material. In Stage 1, 2, 3, and 4 it was 7.6 years, 3.4 years, 2.1 years, and 0.7 years, respectively. The lognormal model seems to be a good approximation of breast cancer survival. The model is consistent both with late excess mortality and with the presence of a cured fraction. It is noteworthy that an excess mortality was observed during the whole follow-up period. Extrapolations from the model should therefore be cautiously judged until supported by observed data.