Biography
Dr. Linet received an M.D. from Tufts University and an M.P.H. from The John Hopkins School of Hygiene and Public Health. She is board certified in internal medicine and general preventive medicine. Dr. Linet was an Associate Professor at The Johns Hopkins School of Public Health before joining the NCI in 1987, where she is Chief of the Radiation Epidemiology Branch. Dr. Linet received the NIH Director's Award for outstanding research, and was elected to the American Epidemiological Society. She is on the Editorial Board of the American Journal of Epidemiology, and served as President of the American College of Epidemiology during September 2004 to September 2005. Dr. Linet is a consultant to the Leukemia Research Fund (England), a member of the Advisory Group on Cancer and the Environment to the American Cancer Society and NCI liaison to the Committee on Environmental Health of the American Academy of Pediatrics. Dr. Linet authored The Leukemias: Epidemiologic Aspects, an internationally recognized text in the field.
Research Interests
- Assess and quantify cancer risks associated with ionizing and non-ionizing radiation
- Identify etiologies of hematopoietic and lymphoproliferative malignancies and related disorders in adults and children
- Evaluate and quantify risks of hematopoietic, lymphoproliferative and related disorders associated with occupational exposure to benzene
- Clarify the relationship of medical conditions, treatments, and other factors that may produce mild immunosuppression, and of familial and genetic factors with risk of malignant lymphoma
- Identify etiologies of brain cancer in adults and children
Radiation and Cancer; Etiology of Hematopoietic, Lymphoproliferative, and Primary Brain Cancers
My research focuses on assessing and quantifying cancer risks linked with occupational, residential, and medical exposures to ionizing and non-ionizing radiation. A series of investigations have examined a wide range of postulated risk factors for hematopoietic, lymphoproliferative, and primary brain neoplasms in adults and children, since the etiologies of these neoplasms are poorly understood. My colleagues and I are conducting cohort and case-control studies to quantify risk, characterize exposure response relationships, examine effect modification by other exposures, evaluate potential confounders, assess alternative methods of measuring exposure, and investigate biologic mechanisms of action.
Ionizing Radiation Exposure and Cancer Risks in Radiologic Technologists
There have been relatively few epidemiological studies of medical radiation workers, and only a very small number include dose estimates. In a collaborative investigation with the University of Minnesota, my colleagues and I have investigated mortality and cancer incidence among a nationwide cohort of 146,022 U.S. radiologic technologists certified 2 or more years during 1926-1982. Compared with SEER cancer registry-based general population incidence rates, the U.S. radiologic technologists had a borderline increase in all solid tumors combined, and elevated breast cancer, thyroid cancer and melanoma, the latter two perhaps reflecting early detection due to easy access to health care.
Using work history questionnaire data provided by 90,000 of the technologists (77% women) during 1983-89 and followed up through 1998, we evaluated risks using internal comparisons and found no increase in total cancer mortality risks, a 3-fold excess of breast cancer mortality among those first employed before 1940 compared to those first working in 1960 or later, and modest increases in mortality risks from the combined grouping of acute myeloid, acute lymphoid, and chronic myeloid leukemia among those first employed prior to 1950 compared to those first working in 1950 or later. There was a 40 percent higher circulatory disease mortality risk among those who first worked before 1940 compared with first working in 1960 or later. Mortality and incidence risks according to work history were similar for breast cancer, and for the combined category of leukemias other than chronic lymphocytic leukemia. Basal cell carcinoma incidence risks were more than 2-fold increased and cutaneous melanoma was also significantly elevated, the latter based on small numbers, for those who first worked before 1940 or before 1950, respectively. The mortality and cancer incidence results are consistent with high occupational radiation exposures before 1950.
With expert health physicists, we are reconstructing exposures to estimate doses for individual workers using computerized and microfiche badge dose monitoring records, from a commercial dosimetry provider and employers; historical badge dose data for radiologic technologists from 3 branches of the military and sentinel hospitals; badge dose and other measurement data from the literature; and questionnaire data on work history, procedures, behavior, and protective gear from the surveys (1983-1989, 1994-1998, and 2003-2005).We will quantify the radiation dose-response and the influence of effect modifiers for specific cancers and other conditions. My colleagues and I are also studying the role of specific molecular and selected genetic factors thought to be directly or indirectly involved in radiation carcinogenesis.
Non-ionizing Radiation, Extremely Low Frequency
To address public health concerns about risk of childhood leukemia from exposures to extremely low frequency magnetic fields (50 or 60 Hertz), we conducted a large case control study with the Children's Oncology Group (a NCI funded clinical trials cooperative group) to evaluate whether magnetic field exposures from power lines and electrical appliances was associated with risk of in childhood leukemia. We found that neither high measured residential magnetic field levels (except possibly magnetic field levels greater than 0.4 microtesla) nor high wire code levels (a proxy measure for close distance of residence to power lines) were associated with significantly increased risks of childhood acute lymphoblastic leukemia. Exploratory analyses evaluating various alternative magnetic field exposure metrics, did not alter our conclusions.
In further analyses based on interview data, we found that childhood acute lymphoblastic leukemia risks were significantly elevated in offspring whose mothers reported use of an electric blanket during pregnancy, and among children whose mothers reported postnatal use of electric blankets, hair dryers, video machines in arcades, and video games connected to televisions. However, patterns for duration or frequency of use of these appliances were inconsistent.
Nonionizing Radiation, Radio Frequency
To investigate whether adult brain cancer was linked with use of cellular telephones, my colleagues and I conducted a large hospital based case control study in the U.S. Risks of gliomas, meningiomas, and schwannomas (acoustic neuromas) were not associated with cumulative use of 100 or more hours or duration of use of more than 60 minutes per day for 5 or more years of cellular telephones. The data did not support the hypothesis that the recent use of hand-held cellular telephones causes brain tumors. Spurred by some experimental and epidemiologic data we evaluated whether non-Hodgkin lymphoma in adults was associated with use of cellular telephones in a large multicenter population-based U.S. case-control study. We found that among regular users compared with those who had never used hand-held cellular telephones, risks of non-Hodgkins lymphoma were not significantly associated with minutes per week, duration, cumulative lifetime or year of first use.
Nonionizing Radiation, Ultraviolet or Sunlight Exposures
My colleagues and I are conducting a methodological study to improve the effectiveness of questionnaires in assessing individual UV or sunlight exposures. To add to the limited research examining how well individuals are able to report their past exposures to UV radiation or sunlight, we enrolled 125 U.S. radiologic technologists (half men, half women, evenly divided between residence in northern and southern latitudes) in a study in which each participant completed a daily activity diary for one week in September 2004 while wearing dosimetry badges to record UV exposure. Participants subsequently completed brief questionnaires about their time and activities outdoors during the week monitored to evaluate the reproducibility and validity of questionnaire responses. Analysis is underway.
Benzene Related Hematopoietic Disorders
A cohort study of mortality and hematopoietic malignancy incidence risks was carried out among 75,000 benzene exposed workers employed between 1949 and 1987 in 12 cities in China. We found a three fold excess risk for non Hodgkin lymphoma (NHL), with risks rising with increasing duration of benzene exposure and associated with benzene exposure more than 10 years prior to diagnosis of NHL. In contrast, a three-fold excess of acute nonlymphocytic leukemia (ANLL) was linked with recent exposures; risk of ANLL did not vary according to exposure duration. Significantly elevated risks were also seen for myelodysplastic syndromes and aplastic anemia, but the number of cases was too small for analysis of duration or other metrics of exposure. There were non-significant excesses of acute lymphoid leukemia and chronic myeloid leukemia.
To examine further the excess risks for hematopoietic malignancies, benzene hematotoxicity, and lung cancer that we had observed in our1972 through 1987 study of Chinese benzene workers, we are currently conducting a case-control cohort study to quantify dose-response and to conduct a detailed between occupational benzene exposure and risk of these outcomes during 1972-1999. We are also conducting a molecular and genetic case investigation of benzene hematotoxiticity.
Keywords
benzene; childhood cancers; genetics; hematopoietic cancers; leukemia; lymphoma; myelodysplastic syndromes; radiation, ionizing; radiation, non-ionizing
Selected Publications
Collaborators
DCEG Collaborators
- Joanne Colt, MPH
- Susan Devesa, Ph.D.
- Michele Doody, M.S.
- Lynn Goldin, Ph.D.
- Gloria Gridley, M.S.
- Thomas Fears, Ph.D.
- Michal Freedman, Ph.D.
- Lynn Goldin, Ph.D.
- Patricia Hartge, Sc.D.
- Michael Hauptmann, Ph.D.
- Richard Hayes, D.D.S., Ph.D.
- Peter Inskip, Sc.D.
- Bu Tian Ji, M.D., Dr.P.H.
- Ruth Kleinerman, M.P.H.
- Quing Lan, M.D., Ph.D.
- Ola Landgren, M.D., Ph.D.
- Kiyohiko Mabuchi, M.D., Dr. P.H.
- Lindsay Morton, Ph.D.
- Elaine Ron, Ph.D.
- Nathaniel Rothman, M.D.
- Patricia Stewart, Ph.D.
- Alice Sigurdson, Ph.D.
- Margaret Tucker, M.D.
- Sholom Wacholder, Ph.D.
- Sophia Wang, Ph.D.
Other NCI Collaborators
- Graca Dores, M.D.
- Deborah Winn, Ph.D.
Other Scientific Collaborators
- Jim Cerhan, M.D., Ph.D., Mayo Clinic
- Wendy Cozen, D.O., University of Southern California, School of Medicine, Los Angeles, CA
- Elizabeth Hatch, Ph.D., Boston University, Boston, MA
- Kari Hemminki, M.D., Ph.D., Karolinska Institute, Stockholm, Sweden
- Gui Lan Li, Ph.D., China Centers for Disease Controls, Beijing, China
- Lene Mellemkjaer, Ph.D., Danish Cancer Society, Copenhagen, Denmark
- Dale Preston, Ph.D., Hirosoft International
- Jorgen H. Olsen, Danish Cancer Society, Copenhagen, Denmark
- Leslie Robison, Ph.D., St. Jude’s Hospital, Memphis, TN
- Eve Roman, Ph.D., University of York, U.K.
- Joachim Schuez, Ph.D., Mainz University, Mainz, Germany
- Richard Severson, Ph.D., Wayne State University, Detroit, MI
- Roel Vermeulen, Ph.D., University of Utrecht, Holland
- Song Nian Yin, M.D., China Centers for Disease Controls, Beijing, China
