Quality control of end results in a Danish adjuvant breast cancer multi-center study

In a Danish multi-center study, quality control was performed on off-study data for high-risk breast cancer patients included in protocols of adjuvant therapy. In the two protocols 4455 patients were randomized and 2477 were registered off-study. Data from these patients were validated by reviewing the patients' records. Incorrect data were observed in 16.2% of the cases who went off-study due to recurrence, other malignant disease or death. In 258 of 2133 patients unidentical locations were demonstrated. Of these, 104 showed a time difference also. A major difference in site of recurrence was found in 107 patients (5.0%), 43 of whom were upstaged from local to a distant recurrence and 64 were downstaged. A time difference of more than 30 days was found in 192 patients (9.0%) and in 17 the difference exceeded 366 days. A time difference only was found in 88 patients (4%). The major parameter in the statistical analysis of the two protocols, i.e. recurrence-free survival, was not significantly influenced by the validation.