Two nationwide registers, the Finnish Cancer Registry and a register of persons entitled to free drugs for hypertension, were linked in a case-control study of the association of breast cancer and use of rauwolfia. Cases were all hypertensive patients in whom breast cancer was diagnosed in 1973. To test the association specifically with rauwolfia, controls were hypertensive women matched with the cases for age and geographic area and approximately matched for duration of treatment for hypertension. There were 109 case-control pairs. Use of any physician-prescribed drugs during the year prior to diagnosis of breast cancer was ascertained from original prescriptions. In the first set of analyses the patients were classified according to the drug used during most days of the year ("main antihypertensive agent"). In the second set a person qualified as a user of the respective drug regardless of the amount taken. The relative risks in the use of rauwolfia, methyldopa, another synthetic antihypertensive or a diuretic as main antihypertensive agent all ranged between 0.90 and 1.11. The results based on use of a drug in any amount were similar. Next, pairs in which duration of treatment for hypertension was different for cases and controls were excluded. The relative risk associated with use of rauwolfia as main antihypertensive agent then increased from 1.00 to 1.30 and the risk associated with use of any amount of rauwolfia from 1.16 to 2.14. Simultaneously, the relative risk in the use of digitalis was raised from 1.33 to 2.67 and of nitroglycerin from 1.00 to 1.71. Cases also used more types of antihypertensive agents simultaneously than controls. There was no association between rauwolfia-use and breast cancer in analyses limited to pairs in which neither case nor control used digitalis. Thus, there was not a consistent drug-specific association between rauwolfia-use and breast cancer in hypertensive patients. An underlying association of hypertension, heart disease or its treatment (digitalis) and breast cancer may have confounded some of the results of this and earlier studies. In conclusion, it is unlikely that use of rauwolfia increases the risk of breast cancer.
The effects of primary site, sex, age, stage and histological type on cancer patient survival were analysed on the basis of the population-based material of the Finnish Cancer Registry from 1985 to 1994. In addition, trends in survival were constructed for the period 1955-1994. Detailed site-specific data are published as Supplement 12 to Vol. 38 of Acta Oncologica. Within a given site, the survival differences by gender were not large. However, because of different site distributions, the average prognosis for female patients, all sites taken together, was superior to that of males: the 5-year relative survival rates (RSR) were 58% and 43%, respectively. In general, older patients had a poorer outcome compared with younger patients (partly because of different stage and histology distributions). Stage was a strong determinant of patient survival. In some cancers with a poor average prognosis the 5-year RSR for localized tumours was reasonable, e.g. 61% for stomach cancer, males, 34% for gallbladder cancer, females, and 29% for lung cancer, males. Most of the survival rates clearly increased over time. In addition to improvements in cancer treatment, changes over time in several other factors affect the trends, such as changes in the stage distribution (early diagnosis as a result of health education, improved diagnostic methods, screening, etc.) and in the composition of the patient material because of changing definitions of cancer (e.g. papilloma versus papillary carcinoma of the bladder, occult carcinoma of the thyroid, and early prostate cancer). The large Cancer Registry material (466,000 patients) enabled accurate estimates of the survival rates of cancer patients in Finland. These rates reflect the effectiveness of the healthcare system as a whole and are useful for planning and evaluation purposes. However, the estimated survival rates are based on grouped data, and cannot be directly applied for predicting the prognoses of individual patients, although they can be used as guidelines.
A total of 3749 workers employed for at least three months in two Finnish glass factories (cohorts A and B) were followed up for cancer in 1953-86 through the Finnish Cancer Registry. In cohort A (1353 men, 1261 women), 106 primary cancers were diagnosed among men, and their standardised incidence ratio (SIR) for all cancers was 99. Among women the risk was low (65 cases, SIR 64). In cohort B (450 men, 685 women), the relative risk of cancer was close to unity for both men (57 cases) and women (75 cases). The risk of cancer was analysed by primary site, type of work, years since first exposure, and age at diagnosis. The only significantly increased risks were those of lung cancer among men (SIR 130, 95% CI 100-167, cohorts A and B combined), and skin cancer among glass blowers (SIR 625, 95% CI 129-1827). An increased risk of lung, stomach, and colon cancer as well as of brain tumours has been reported in previous studies. It is postulated that the excess risk of lung cancer, detected in this study, can also be accounted for by lifestyle, and not only by possible occupational exposures, because a similar excess risk of lung cancer has been found previously for all industrial workers in Finland. Although the risk of stomach cancer in this study was increased among glass blowers, it was not high in the largest groups of plain glass workers. The risks of tumours of the central nervous system and colon were not increased either.
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In the analysis of cause-specific survival, the causes of death must be known. For single-cancer patients with a known cause of death, the estimation of the cause-specific survival rate is straightforward. For multiple-cancer patients with two primary cancers, however, the analysis of cause-specific survival rates is more complex, particularly if the cancers are of the same primary site. In these situations, a concept of cancer-specific survival may also be distinguished from cause-specific survival. Cancer-specific survival rates are studied here by introducing two models, the primary one where the death from cancer is attributed to one of the cancers, and an alternative where such an attribution is not necessary. The models are illustrated using data on patients with multiple breast cancers. The model-based survival rates are compared with each other and with the corresponding relative survival rates based on analogous modelling of relative survival. The results show that for the subsequent breast cancer, the cancer-specific survival rates based on the alternative, where the distinction between the cancers as a cause of death was not necessary, tended to be higher than those based on that distinction. It is thus possible that the subsequent cancer was too often coded as a cause of death, particularly when being localized at diagnosis.
The Finnish Cancer Registry notifications of colorectal cancer diagnosed in Finland in 1975 were compared against original patient records, and hospital archives were searched for unregistered cases. 1027 cases had been registered. 4.7% of them were erroneous: 1.6% had been diagnosed before or after 1975, 1.5% had no verifiable malignancy, and in 1.7% the correct primary site was other than the colorectum. Unregistered cases amounting to 1.2% of the total were found. Only one case was unknown to the Cancer Registry, the others had been inaccurately registered as to the site of tumour or date of diagnosis. The corrected age-adjusted incidence rate (males/females) of colon cancer was 8.2/8.6 and that of rectal cancer 9.1/6.1 per 100,000. In the light of the present study, cancer registry data in Finland offer a reliable basis for timetrends and international comparisons of incidence rates of colorectal cancer.
Cancer registries should pay great attention to the quality of their data, both in terms of completeness (all cancer patients in the population are registered) and accuracy (data on individual cancer patients must be correct). In addition to technical measures in the data processing, different types of checks and comparisons should be routine practice. Active research policy and ambitious, research-oriented staff with competence in medicine, biostatistics and computer science are essential in terms of maintaining good data quality.