BACKGROUND: The risk of contralateral breast cancer is increased twofold to fivefold for breast cancer patients. A registry-based cohort study in Denmark suggested that radiation treatment of the first breast cancer might increase the risk for contralateral breast cancer among 10-year survivors. PURPOSE: Our goal was to assess the role of radiation in the development of contralateral breast cancer. METHODS: A nested case-control study was conducted in a cohort of 56,540 women in Denmark diagnosed with invasive breast cancer from 1943 through 1978. Case patients were 529 women who developed contralateral breast cancer 8 or more years after first diagnosis. Controls were women with breast cancer who did not develop contralateral breast cancer. One control was matched to each case patient on the basis of age, calendar year of initial breast cancer diagnosis, and survival time. Radiation dose to the contralateral breast was estimated for each patient on the basis of radiation measurements and abstracted treatment information. The anatomical position of each breast cancer was also abstracted from medical records. RESULTS: Radiotherapy had been administered to 82.4% of case patients and controls, and the mean radiation dose to the contralateral breast was estimated to be 2.51 Gy. Radiotherapy did not increase the overall risk of contralateral breast cancer (relative risk = 1.04; 95% confidence interval = 0.74-1.46), and there was no evidence that risk varied with radiation dose, time since exposure, or age at exposure. The second tumors in case patients were evenly distributed in the medial, lateral, and central portions of the breast, a finding that argues against a causal role of radiotherapy in tumorigenesis. CONCLUSIONS: The majority of women in our series were perimenopausal or postmenopausal (53% total versus 38% premenopausal and 9% of unknown status) and received radiotherapy at an age when the breast tissue appears least susceptible to the carcinogenic effects of radiation. Based on a dose of 2.51 Gy and estimates of radiation risk from other studies, a relative risk of only 1.18 would have been expected for a population of women exposed at an average age of 51 years. Thus, our data provide additional evidence that there is little if any risk of radiation-induced breast cancer associated with exposure of breast tissue to low-dose radiation (e.g., from mammographic x rays or adjuvant radiotherapy) in later life.
A case-control study of breast cancer among tuberculosis (TB) patients in Denmark (1937-1954) was conducted to provide additional information on the radiation risk associated with low-dose chest fluoroscopy exposures. Records of 46013 TB patients were linked to the Danish Cancer Registry and 125 subsequent female breast cancers identified. Medical records were located for 89 (71%) of these women who developed breast cancer and on 390 controls, who were individually matched to cases on age and calendar year of TB diagnosis, and survival. Common risk factors for breast cancer such as nulliparity (relative risk (RR) = 2.5) and high relative weight (RR = 2.6) were also identified in this population of TB patients. However no risk was evident with exposure to any type of fluoroscopy (RR = 0.6; 95% CI = 0.2-1.4), or to fluoroscopies performed to monitor lung collapse therapy (RR = 0.8; 95% CI = 0.5-1.4). Although based on only 7 breast cancers, there was a suggestion of an increased risk among women who received greater than 1 Gy to their breasts (RR = 1.6; 95% CI = 0.4-6.3). Because of the infrequent use of fluoroscopy in our study, the breast doses were too low, 0.27 Gy on average, to expect to detect a significant elevation in breast cancer risk overall. The findings do suggest, however, that current estimates of breast cancer risk following radiation are not greater than presently accepted, and that a relative excess of 40 per cent can be excluded with reasonable confidence following breast doses on the order of 0.3 Gy.
Cancer incidence data for Circumpolar Inuit populations were developed and compiled from Greenland, Canada and Alaska from 1969 to 1988 to provide the largest possible base of data for documenting the unusual patterns of cancer previously reported for these populations. Cancer incidence and population data were transferred to the Danish Cancer Registry. Coded information from various ICD-classifications and codes for the basis of diagnosis were transformed to one format, enabling joint analysis. Standard descriptive analysis was carried out with presentation of number of cases, crude incidence rates (CR), age-standardized rates (world) (ASR), cumulative rates to age 64 years, and indirectly standardized ratios (SIR) to the populations of Connecticut (USA), Canada and Denmark. The resulting database can be used to support collaborative international research among the Inuit populations.
BACKGROUND: Studies of groups of patients given injections of the alpha-emitting x-ray contrast medium Thorotrast may provide information on human alpha-ray carcinogenesis. PURPOSE: We re-established a formerly identified cohort of neurological patients receiving injections of Thorotrast for cerebral arteriography and assessed their incidence of cancer. METHODS: Using the national population register, the Danish Cancer Registry, and other registers, we determined the incidence of cancer among Thorotrast-injected patients. Incidence ratios were standardized to the general population and computed for different cancer sites. RESULTS: The cumulative risk for cancer at all sites (excluding brain tumors where the standardized incidence ratio [SIR] was 28) reached 86% 50 years after Thorotrast injection. SIR was greatly elevated at all sites except the brain and CNS (3.3, 95% confidence interval = 3.0-3.7), mainly because of liver cancers (SIR = 126) as well as leukemia (SIR = 10) for which a relationship was found between the time since injection and the estimated dose (but not the age at injection). Other sites with significantly increased risks of cancer included the gallbladder and extrahepatic bile ducts (SIR = 14), peritoneum (SIR = 8.6), sites of multiple myeloma (SIR = 4.6), metastatic sites (SIR = 12), and unspecified sites (SIR = 11). Cancers of the lung and breast also occurred in significant excess, but no relationship between SIR and volume of injected Thorotrast or time since injection was observed. Cancer risk was increased at most other sites, although this increase was not statistically significant. CONCLUSION: Alpha radiation may account for the increased risk of tumors of the liver, gallbladder, and peritoneum as well as leukemia and multiple myeloma, whereas confounding factors most probably contribute to the increased risks at other sites.
The results of an international, collaborative study of cancer in Circumpolar Inuit in Greenland, Canada, Alaska and Russia are summarized. A total of 3 255 incident cancers were diagnosed from 1969 to 1988 among 85 000-110 000 individuals. Indirect standardization (SIR) based on comparison populations in Connecticut (USA), Canada and Denmark showed excess risk of cancer of the lung, nasopharynx, salivary glands, gallbladder and extrahepatic bile ducts in both sexes, of liver and stomach cancer in men, and renal and cervical cancer in women. Low risk was observed for cancer of the bladder, breast, endometrium and prostate, and for non-Hodgkin lymphoma, Hodgkin's disease, leukaemia, multiple myeloma and melanoma. Age-standardized incidence rates (ASRs) of cancer of lung, cervix, nasopharynx and salivary glands among Inuit were among the world's highest as were rates in women of oesophageal and renal cancer. Regional differences in ASRs within the Circumpolar area were observed for cancer of the cervix, lung, colon and rectum, liver, gallbladder and breast. The differences in the Inuit cancer incidence pattern to some extent reflect known variations in lifestyle, diet and other exposures, as well as implementation of cancer control measures. Future research addressing possible individual differences are needed to evaluate environmental and genetic factors in etiology and evaluate intervention studies.
The cancer pattern among Inuit in the Circumpolar area have shown marked differences to other populations in the world. The current paper summarises important risk factors in Greenland, including the physical environment, diet, alcohol, tobacco and other lifestyle factors. Details on population structure and history, health care and cancer registration are also included. This information is important for the interpretation of the incidence pattern for the Circumpolar Inuit collectively and for the understanding of differences between the various Inuit populations of the North.
Cancer of the oesophagus, stomach, small intestine, colon, rectum, liver, gallbladder, biliary tract and pancreas was studied in the Inuit populations of Alaska, Canada and Greenland. Indirect standardization to the populations in Canada, Connecticut (USA) and Denmark was used. High risk of oesophageal cancer was observed in both sexes with standardized incidence ratios (SIRs) of up to 7. An increased risk of colon and rectum cancer occurred among Alaskan Inuit compared with the Inuit populations in Canada and Greenland, which had lower rates. Liver and gallbladder cancer rates were high, with SIRs of 1.5 to 4.1, whereas there were no differences in pancreatic cancer in the populations compared. Dietary habits, alcohol and tobacco consumption are believed to play an important role in most of the observed cancer patterns, but for liver cancer hepatitis B virus infection is also believed to have a causal role.