Dr. David B. Thomas

My expertise is in the following areas:
cancer epidemiology
breast cancer epidemiology
cervical cancer epidemiology
tobacco-related cancer
steroid contraceptives
cancer screening

From 1978 to 1992, Dr. Thomas coordinated for the World Health Organization (WHO) a collaborative study in 11 countries on five continents. The purposes of this study were to assess the effects of steroid contraceptives and other factors on risks of cancers of the breast, cervix, ovary, endometrium, and liver. The WHO study showed that women are at increased risk of cervical cancer if, prior to marriage, their husbands frequently visited prostitutes and did not use condoms during those visits. Certain strains of human papillomaviruses (HPV) are the sexually transmitted agents that are probably necessary causes of cervical cancer, and Dr. Thomas conducted a subsequent study in Bangkok that confirmed the role of prostitutes as a reservoir of oncogenic HPV strains, and of their customers as vectors for transmission of these viruses to women in the general population. That study also provided evidence that persistence of oncogenic types of HPV, which leads to carcinogenesis, is associated with endgenous and exgenous hormonal factors and smoking, as well as immunosuppression. With the possible exception of Vitamin A, which may inhibit progression from in situ to invasive disease, other co-factors appeared to act earlier in the carcinogenic process.

In 1988, Dr. Thomas initiated a randomized trial of breast self-examination (BSE) in Shanghai, China. More than 267,000 women in 519 textile factories were interviewed to obtain information on risk factors for breast cancer, and randomly assigned by factory to a BSE instruction group or control group. Women in both groups were monitored for the development of benign and malignant breast tumors, and for mortality through 2000. Mortality from breast cancer was the same in the instruction and control groups, providing strong evidence that teaching BSE does not reduce deaths from breast cancer. This study population also serves as a resource for independently funded investigations conducted in collaboration with other investigators at the Center. One such study showed that induced abortions did not alter the incidence rate of breast cancer. Other investigations have included studies of: the determinants of cell proliferation in benign and malignant tumor tissue and in normal tissue adjacent to tumors; the role of nutritional factors in the etiology of benign and malignant breast diseases; the role of breast cancer genes BRCA-1 and BRCA-2 in the development of breast cancer; the possible role in the etiology of breast cancer of polymorphisms in multiple genes involved in hormone biosynsthesis and catabolism, and of genes for certain growth factors and hormone receptors; and the possible etiologic role of electromagnetic field exposure in the etiology of breast cancer. In addition, risks of other types of cancer in relation to contraceptive methods and occupational exposures have been assessed in women in the trial cohort.

Dr. Thomas also conducted a study in Seattle that showed that radiographic densities and certain types of calcifications on mammograms in women under 50 can be used to identify women at increased risk of subsequent breast cancer.

Dr. Thomas is former Head of both the Epidemiology and Breast Cancer Programs at the Fred Hutchinson Cancer Research Center, and former Director of the Cancer Surveillance System of Western Washington which is a population-based cancer registry.

Plans are underway with colleagues to utilize the resources from the studies in Shanghai to conduct additional investigations into the etiology and natural history of breast and other cancers. Studies under consideration include: use of microarray technology to identify determinants of breast cancer development in benign breast tissue and of survival in malignant breast tissue; development and testing of biologically based mathematical models to investigate mammary carcinogenesis.