The data set
Five well-defined geographical regions comprising approximately 50% of the Finnish population were selected. Using the files of the Finnish Cancer Registry women diagnosed with breast cancer within these regions in 1991 and 1992 were identified. Hospitals, practicing physicians, and pathologic and hematologic laboratories are requested to report to the Finnish Cancer Registry all cases of cancer that come to their attention. In addition, all death certificates in which cancer is mentioned are transferred from the files of the Statistics Finland to the Cancer Registry each year.

A computer search of the files of the Finnish Cancer Registry identified a total of 2,930 breast cancer cases diagnosed in these regions in 1991 to 1992, which constitutes 53% of all 5,551 breast cancers diagnosed in Finland during this time period.

Using structured data collection forms, the individual clinical data of the patients were extracted from the hospital records, which were reviewed. An effort was made to obtain detailed clinical information on 50 characteristics, including the variables available in the present system, and follow-up data. In addition to the hospital case records, relapse and survival data were obtained from the files of the Finnish Cancer Registry and the hospital registries, when available.

For the study inclusion we required the following minimum data to be available: date of breast cancer diagnosis; age at diagnosis; information on other malignancies than breast cancer in history, including data on bilateral breast cancer; postsurgical size of the primary tumor and axillary nodal status; follow-up data; and vital status data at the end of follow-up.

This minimum information was available in 2,656 (91%) of the 2,930 eligible patients. The percentage of the patients with the minimum information available varied from 79% in southwestern to 97% in eastern Finland. In addition to the 2,656 patients with the minimum clinicopathologic information available, we included 186 further patients who fulfilled the minimum clinicopathologic information and were diagnosed with breast cancer within the same geographic regions during the same time interval, but who were not identified in the original computer search because the place of residence was outside the specified regions.

Thus the total number of patients in the Finprog series is 2,842. The median follow-up time for the unrelapsed patients is 9.5 years (range, 0.25 to 10.8 years, however, if two patients who moved out of the country shortly after diagnosis are excluded, the range is 8.2-10.8 years).

From the website database, used as the source for the survival estimates, all personal identification information has been deleted and replaced by internal coding. In addition the following patients have been excluded (a single patient may have been excluded for more than one reason):
- lobular carcinoma-in-situ (n=17)
- ductal carcinoma-in-situ (n=186)
- patients with distant metastasis at the time of diagnosis(n=136)
- synchronous or metachronous bilateral breast cancer (n=261)
- malignancy other than breast cancer in history (except for basal cell carcinoma or cervical carcinoma in-situ;n=235))
- women who do not undergo breast surgery (n=42)
leaving 2,032 patients in the final data set.

The variables ..