National Cancer Institute monograph最新文献

A case-control study involving interviews with 1,200 patients with esophageal cancer and 1,200 population-based controls has been initiated in Linxian, a county in North Central China with perhaps the world's highest mortality rates for this tumor. Here we describe the rationale, study methods, and results of a pilot study that established the feasibility of the investigation.

A case-control study is currently under way in Beijing, People's Republic of China, involving approximately 165 patients with invasive moles or choriocarcinoma, 165 with hydatidiform moles, and 330 population controls, who were matched to the patients with invasive moles or choriocarcinoma on age and interval since last pregnancy. The interviews are focused on a number of suspected risk factors, including previous pregnancy outcomes, history of hydatidiform mole, medical factors, drug usage, family history, and diet. A brief background of the study and methods as established through a previous pilot study are given.

Three cancer prevention trials are currently in their early phases at The Fred Hutchinson Cancer Research Center, the University of Washington School of Public Health and Community Medicine, and the Swedish Hospital. All 3 studies are randomized and placebo controlled. One large-scale study involves the daily administration of retinoids to persons with asbestos-related lung disease in an attempt toward reduction of their high risk for bronchogenic carcinomas and mesotheliomas. A second study involves administration of the same agents to long-term heavy smokers; a substantial feasibility and toxicity pilot study will precede a full-scale prevention trial. In the third trial, folic acid administration is evaluated in relation to the progression and regression of cervical dysplasia among women with abnormal Pap smears. We report here the rationale and the design for these 3 studies.

The pattern of incidence rates according to age for many forms of cancer has been found to be in reasonable accord with the equation or some modification of it: It = btk, where It is the incidence rate at age t, and b and k are constants. An alternative equation postulates that the risk of cancer is determined not by the age of a person but by the length of time exposed to a carcinogenic agent: It = b(t-w)k, where t-w represents the "effective exposure" between first exposure and clinical evidence of cancer. Mesothelioma rates in asbestos insulation workers were strongly related to time from onset of exposure regardless of age at first exposure. However, the same pattern was not evident for lung cancer mortality in the same workers compared with blue collar worker controls from the American Cancer Society Cancer Prevention Study I. Lung cancer mortality by attained rates and by duration of smoking were shown for current smokers of cigarettes only for the Cancer Society study, classified by age at which they started smoking. Lung cancer results were also given for men who never smoked regularly.

More is known about ionizing radiation as a cause of human cancer than about any other carcinogen. Most of this knowledge is derived from the studies conducted by the Atomic Bomb Casualty Commission and Radiation Effects Research Foundation on about 100,000 Japanese survivors of the atomic bombing in 1945. The importance of these studies is based on the large size of the exposed population and the fact that individual estimates of radiation dose were possible. These factors and the combined excellence of the centralized vital statistics reporting and population registration systems in Japan have made feasible the continuing longitudinal studies of cancer mortality by site in relation to radiation dose over a span of more than 30 years. Excellent voluntary cooperation by the survivors has enabled the continuation of a biennial physical examination program which has made possible the acquisition of blood for studies of radiation-induced chromosomal aberrations and mutations at the level of specific genes. Similarly, with the cooperation of local universities, hospitals, and physicians, tumor and tissue registries necessary for the study of cancer incidence have been developed. An autopsy pathology program has enabled study of the accuracy of cause of death certification.

The Birmingham, England, Cancer Registry is so organized that every case of cancer in its territory of 5,200,000 persons is included. This coverage allows the staff to detail every epidemiologic aspect of the cancer experience of a whole population. For example, this registry system made it possible for us not only to demonstrate that the Birmingham region had four times the incidence of scrotal cancer as another region had but to identify the locations and the specific practices in the workplace responsible for the excess. The result was the successful adoption of protective measures. Other instances are presented of the inestimable value of a population-based registry to cancer epidemiology.

Many populations are exposed to health hazards, particularly workers in the health care industry. Yet practical reasons make it impossible or unfeasible for investigators to meet the technical requirements of the cohort method. One such experience is detailed of hospital workers who were members of a large health care workers' union. Given the fact of exposure to known or suspected hazards, two strategies are urged: 1) projection of work toward adoption of rules regarding organizational settings that would make cohort investigation practical when necessary, and 2) development of alternate means by which work can be assessed when cohort analysis cannot be realistically conducted.

Those who conduct cohort studies in cancer epidemiology increasingly use biochemical analyses as an important component. Some of the potentially important considerations when banked blood is used include the conditions and temperature of storage, effects of thawing, and the stability of specific substances under prolonged subfreezing temperatures. I have reviewed a selected number of biochemical substances.

Numerous mortality studies may be found in publications of the life insurance industry dating back about a century. Examples presented include mortality in asthma history (1903), overweight (1844-1905), and hypertension (1907-11). The favorable effect of underwriting selection on mortality was recognized early, and standard insurance mortality tables in North America have always distinguished between select and ultimate mortality rates. The mortality ratio has been the traditional measure of excess mortality in insurance follow-up studies. Similar mortality studies in the medical literature before 1920 are extremely difficult for investigators to locate. One important exception with regard to methodology and completeness of comparative mortality and survival results was a 20-year follow-up of pulmonary tuberculosis patients after discharge that was reported in 1908.

Cohort studies have particular advantages in confirming results of retrospective or case-control studies in those situations in which case-control studies are no longer feasible. In circumstances, the cohort study may involve randomization, thus reducing selection bias, but ordinarily there will have been self-selection by individuals as to the group in which they will fall. Investigators should analyze data from a cohort study so as to take the passage of time into account. Variables anticipated to have effects should be accounted for by stratification, if feasible, or by mathematical modeling, if necessary. Results should be interpreted with care, and qualifications should be made on any interpretations, including qualifications relating to the propriety of the mathematical model used. When long latencies are a factor, and particularly when exposure is initiated late in life, establishment of a positive role for the exposure can be difficult. Case-control and other epidemiologic studies are biased toward identification of exposures leading to outcomes of a unique nature but fail to identify more serious exposures with adverse outcomes which are more commonplace.