Conclusions
Over sixty years of data exist to support a role for environmental factors in the etiology of breast cancer. Most of the evidence is circumstantial. Research to date has been limited and suffers from lack of a coherent conceptual framework and access to adequate databases. The CBCRP has an opportunity to remedy the situation. California represents the ideal location for conducting a comprehensive evaluation of the environment and breast cancer. With its diversity of populations and physical environment, extensive environmental databases and infrastructure for collecting new data, California may be the only place where such a comprehensive investigation could be done.
A series of steps were proposed to initiate a research program in breast cancer and the environment sponsored by the CBCRP. Beginning with previously collected information, new statistical methods could be used to calculate incidence and mortality rates for breast cancer within smaller geographic units, thereby providing a clearer window on variation across the state. Existing databases could be augmented through complementary data collection: information on residence history, social class, and access to health care represent important potential additions to the California Cancer Registry. Patients in the Registry as well as participants in epidemiologic studies could be linked through residence history to a variety of environmental exposures through geo-coding. Much of the environmental exposure information needed for such investigations is already collected routinely under public mandate and could easily be supplemented in areas where breast cancer incidence is highest. Interdisciplinary investigations could build upon these databases to develop new biomarkers, examine novel biochemical pathways for breast development, identify markers of genetic susceptibility to environmental exposures, and study environmental factors that act during critical windows of susceptibility in a woman's lifetime.
Why should the CBCRP sponsor such an ambitious research program when there are other research priorities? Environmental exposures are likely to be weak, contributory causes of breast cancer, neither necessary nor sufficient for disease. Other priorities would seem to be more pressing: the development of new therapeutic drugs, novel methods for early detection, and addressing inequalities in health care. In fact, the proposed research program addresses each of these areas, and would provide information that is needed before such investigations can proceed. Environmental factors will tell us a great deal about the biochemical pathways that lead to breast carcinogenesis, including aberrant cell signaling, elevation of oxidative stress, and modulation of estrogen metabolism, and this information will have important applications to treating and preventing breast cancer. At present, we do not know the extent to which current methods of breast cancer screening are successful, and this can only come by examining long-term trends in stage at diagnosis of breast cancer and identifying subgroups of women for whom screening has not been offered or followed through with effective treatment. Inequalities in health care have to first be understood before they can be addressed. Unfortunately, the extent to which geographic, economic, and social barriers exist to effective, high quality treatment for breast cancer has not been well studied.
Why should such a program be attempted in a time of limited funding? A CBCRP program on breast cancer and the environment would be an effective use of funds. At present, citizens living in regions with high rates of breast cancer often lobby separately for funding. Several studies of breast cancer have been conducted in very small geographic areas in California, and none have provided definitive results. An environmental research program sponsored by CBCRP would provide a coherent research program and infrastructure to follow up on these small studies with more definitive investigations. Such a program would help to avoid misuse of resources and help lay to rest clusters that represent false alarms. Anxiety over potential breast cancer clusters and persistent fears in the public about the role of pesticides, ionizing radiation, and other modifiable breast cancer risk factors need to be addressed in a comprehensive, interdisciplinary manner. To do otherwise would be irresponsible.
