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,
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 ..