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Biomedical subjects

G H Lyman

Publications and source records attributed to G H Lyman.

At least 55 records · Page 3Linked to original sources
PubMed1997

Cancer in the elderly. Epidemiologic and clinical implications.

Cancer is a major problem for the older population. The incidence of most malignancies increases with age, with cancer being the second most common cause of death in persons older than 65. With the decline in deaths related to cardiovascular diseases, cancer is becoming an even more prominent cause of death among the elderly. Despite the advances in cancer prevention and treatment over the past 20 years for persons under 50, the mortality has not improved for older persons. In this article we explore the interactions of cancer and age that may be of interest to the practitioner, after reviewing the epidemiology of cancer in the elderly.

Age Distribution↗
PubMed1996

Lymphatic mapping and sentinel node biopsy in the patient with breast cancer.

OBJECTIVES: To identify the sentinel lymph node(s) (SLN[s]) (the first node[s] draining the primary tumor in the regional lymphatic basin) in patients with invasive breast cancer and to test the hypothesis that the histologic characteristics of the SLN predict the histologic characteristics of the remaining lymph nodes in the axilla. DESIGN: A prospective trial. PARTICIPANTS: Sixty-two patients with newly diagnosed invasive breast cancers. INTERVENTION: Patients underwent intraoperative lymphatic mapping using a combination of a vital blue dye and filtered technetium-labeled sulfur colloid. The SLN was identified and removed, followed by a definitive cancer operation, including a complete axillary node dissection. MAIN OUTCOME MEASURE: The metastatic distribution in the axilla was determined in patients with occult nodal disease. RESULTS: The SLN was successfully identified in 57 (92%) of 62 patients using the 2 lymphatic mapping procedures. After localization, 18 patients (32%) were found to have metastatic disease, and the SLN tested positive in all 18 patients. There were no "skip" metastases, defined as an SLN that tested negative with higher nodes that tested positive. In 12 (67%) of 18 patients with metastatic disease, the SLN was the only site of disease. The metastatic distribution significantly favored SLN involvement. Among subjects with discordant nodal involvement, the probability of observing the distribution of SLN involvement by chance is very small (P<.001). CONCLUSIONS: This study confirms that lymphatic mapping is technically possible in the patient with breast cancer and that the histologic characteristics of the SLN probably reflect the histologic characteristics of the rest of the axillary lymph nodes. The procedure also allows the pathologist to focus the histologic examination on 1 or 2 nodes, potentially increasing the yield of positive dissections and the accuracy of staging.

Axilla↗
PubMed1996

Evaluation of new putative tumor markers for melanoma.

BACKGROUND: The early diagnosis of recurrent melanoma can contribute to better outcome if the disease can be surgically resected or if the metastases are responsive to systemic therapies. Lipid-associated sialic acid (LASA-P) and the S-100 protein (S-100) were evaluated as tumor markers for melanoma with the goal of early detection of recurrence. METHODS: Sixty-seven patients were identified who had levels of S-100 and LASA-P drawn during their clinical course. A multivariate regression analysis was performed to determine the significance of the serum markers in relation to other prognostic factors for melanoma. RESULTS: After a median follow-up of 30 months, 58 patients had recurrences, and 49 patients died of disease. LASA-P elevation was not associated with the time to recurrence (p = 0.2176) or survival (p = 0.2507). S-100 positivity was a significant predictor of recurrence (p < 0.0001) and survival (p = 0.0059). The median time to recurrence for S-100-positive and S-100-negative patients was 7.6 and 33.8 months, respectively. The median survival time was 59.2 months for S-100-negative patients and 29.6 months for patients positive for S-100. CONCLUSIONS: Serum S-100 shows significant correlations to both time to recurrence and survival and could be useful in the clinical detection of malignant melanoma.

Adult↗
PubMed1996

Patients' attitudes regarding out-of-hospital blood transfusion.

BACKGROUND: While the administration of blood transfusions outside of the hospital has become more prevalent, little is known about patients' attitudes regarding this practice. STUDY DESIGN AND METHODS: Twenty-nine adult patients who regularly received blood transfusions in a hospital's outpatient clinic and had never received home transfusions were surveyed. Linear analogue and categorical monetary scales were used to evaluate their responses to a series of questions. RESULTS: At the time of the survey, 27 study participants (93%) did not want home transfusions, and 21 (72%) thought home transfusions posed a greater risk than hospital based transfusion. More than half (56%) of the participants were unwilling to pay more for a home transfusion for themselves than for an outpatient hospital-based transfusion. Participants were willing to pay more for a home blood transfusion for a hypothetical patient requesting transfusions at home. The lack of available transportation and poor patient health were identified as important factors in determining how much more they would be willing to pay for transfusions at home. CONCLUSION: While blood transfusions at home may become more accessible, many patients may prefer to receive their transfusions in the hospital, probably because home transfusions are thought to pose a greater risk. A patient's health and the availability of transportation were determined to be important factors in decisions about how much more money to spend for transfusions at home than for those in an outpatient hospital setting.

Adult↗
PubMed1995

The increasing incidence of malignant gliomas and primary central nervous system lymphoma in the elderly.

BACKGROUND: Studies indicate that the incidence of primary malignant brain tumors in the elderly is increasing, but this may reflect increased case ascertainment due to the introduction of computed tomography (CT) scanning. In addition, tumor histology was not available in these studies. This study was conducted to determine whether the incidence of primary malignant brain tumors in the elderly in Florida is increasing and to verify the histology of these increases. METHODS: Using the number of primary malignant brain tumors reported to the Florida Cancer Data System (FCDS) when CT scanning was available, incidence rates per 100,000 people were calculated. Incidence density ratios (IDRs) were calculated for 1986-1989 relative to 1981-1984. RESULTS: Tumor incidence at ages 20-64 years increased from 5.7 in 1981-1984 to 5.9 in 1986-1989, with an IDR of 1.05 (not significant). The incidence in those aged 65 years or older rose from 14.8 to 18.3, with an IDR of 1.23 (P < 0.001). The increase was 15% in those aged 65-69, 16% in those 70-74 years, 30% in those 75-79 years, 36% in those 80-84 years, and 254% in those 85 years or older. Indicence density ratios in those aged 65 years or older were 0.92 (not significant) for astrocytoma, 2.7 (p < 0.001) for anaplastic astrocytoma, 1.32 (p < 0.001) for glioblastoma and 3.56 (p < 0.001) for lymphoma. In those aged 65+ the incidence of all cancers rose 7.6% (not significant), and the incidence of pancreatic cancer (another neoplasm that requires CT scanning for diagnosis) rose 0.34% (not significant). CONCLUSIONS: The incidence of primary brain tumors in elderly Floridians has increased. This increase is independent of increased case ascertainment associated with the introduction of CT scanning and independent of a general increase of all cancers. The rise in brain tumor incidence is observed in anaplastic astrocytoma, glioblastoma, and lymphoma but not astrocytoma. This study confirms the increase is histologically specific and not due to increased case ascertainment. Further investigation into the etiology of this increase is warranted.

Adolescent↗
PubMed1995

Timing of weight gain and breast cancer risk.

BACKGROUND: Obesity and body-fat distribution have been associated with the incidence of breast and endometrial cancers. It may be critical to determine if the timing of weight gain during periods of hormonal change, such as menarche, pregnancy, or menopause, has different biologic effects, especially secondary to differences in the localization of body fat during these periods. The objective of the current study was to determine if excess weight in any particular decade of life or the timing of weight gain was more significant relative to breast cancer risk. METHODS: Anthropometric, medical, and hormonal histories were obtained from 218 consecutively recruited, newly diagnosed patients with breast cancer admitted to the H. Lee Moffitt Cancer Center and Research Institute (Tampa, FL) and 436 control subjects, matched in a two to one ratio for age and menopausal status. RESULTS: A weight gain of 15 pounds or more was observed for 63.8% of the patients compared with 49.3% control subjects (P = 0.0006) from age 30 to current age. Similarly, more than 48% of cases gained more than 15 pounds from ages 16 to 30 compared with 37% (P = 0.01) of the control population. Although weight gain from age 16 to adulthood was significantly higher in patients with breast cancer at each decade when compared with control subjects, a significant and independent association between weight at age 30 (P < 0.0001) and risk of breast cancer was noted. CONCLUSION: Women who progressively gain weight from puberty to adulthood, and specifically in the third decade of life, should be considered at a higher risk for developing breast cancer.

Adult↗
PubMed1995

A cost analysis of hematopoietic colony-stimulating factors.

The administration of hematopoietic colony-stimulating factors (CSFs) to reduce the severity and duration of neutropenia associated with systemic chemotherapy has become widespread, although the appropriate use of these agents has not yet been fully defined. A cost model based on decision theory is presented for three therapeutic choices in these patients: no CSF, prophylactic CSF, and therapeutic CSF. Baseline probabilities were derived from a prospective, randomized, placebo-controlled trial of G-CSF in patients receiving systemic chemotherapy. Application of the model to institutionally generated cost figures provides comparative estimates of excess cost favoring the prophylactic use of CSFs. Model thresholds were calculated based on sensitivity analysis comparing no CSF to prophylactic CSF, and therapeutic CSF to prophylactic CSF. Guidelines are provided based on this model that are consistent with those adopted by the American Society of Clinical Oncology.

Antineoplastic Agents↗
PubMed1994

High levels of interleukin-6 are associated with low tumor burden and low growth fraction in multiple myeloma.

Interleukin-6 (IL-6) is a multifunctional cytokine postulated to play a central role as a growth factor for multiple myeloma (MM). We evaluated the spontaneous secretion of IL-6 in supernatants of Ficoll-Hypaque--enriched bone marrow (BM) cultures from 35 patients with MM. The levels of IL-6 were correlated with biological and clinical characteristics of the disease. High levels of IL-6 production defined a subgroup of patients with low tumor burden as determined by lower serum beta 2-microglobulin (B2M) (P = .02) and lower percentage of myeloma cells infiltrating the bone marrow (P = .003), higher synthetic rates of monoclonal protein (P = .006), and low proliferative compartments as measured by the percentage of Ki-67--positive myeloma cells. Patients with high proliferative fractions (Ki-67--positive myeloma cells > 20%) had significantly lower levels of IL-6 when compared with patients with low proliferative fractions (P = .005). Our findings do not support IL-6 as a major growth factor for MM, but demonstrate an association of high levels of IL-6 secretion with low tumor cell burden and low proliferative fraction.

Aged↗
PubMed1994

The effect of changing disease risk on clinical reasoning.

OBJECTIVE: To assess the ability of health care professionals to evaluate the effect of clinical test results in different settings. DESIGN: Subjects were presented with a series of generic clinical scenarios in which information about the test performance and the pretest probability of disease was varied. The subject estimates of posttest probability were compared with those calculated on the basis of Bayes' theorem. PARTICIPANTS: Fifty health care professionals, including 31 physicians and 19 nonphysicians, associated with a university teaching hospital. MEASUREMENTS AND MAIN RESULTS: Under a variety of testing conditions, both the physicians and the nonphysicians inaccurately estimated the posttest probability of disease. Based on a logarithmic transformation, the error in probability estimation was divided into a portion related to the pretest probability of disease and a portion related to the test performance. Most of the error in posttest probability estimation was associated with the incorrect use of pretest probabilities. The subjects consistently overestimated the posttest probability of disease expected under Bayes' theorem, with increasing error associated with decreasing pretest probability. Physician estimates of posttest probability increased with increasing likelihood ratios for each scenario. Nonphysician estimates of posttest probabilities increased with increasing likelihood ratios for a positive test, but the estimates associated with a negative test result were inconsistent. CONCLUSIONS: Physicians and nonphysicians overestimate posttest probabilities with increasing error associated with decreasing disease risk. Some nonphysicians may not fully understand the effect of test performance on risk estimation, particularly in the setting of a negative test. Health care professionals should receive training in the proper evaluation of test information, with particular emphasis on the influence of pretest disease risk on the posttest probability of disease.

Bayes Theorem↗
PubMed1994

Management of chemotherapy in a pregnancy complicated by a large neuroblastoma.

BACKGROUND: The English literature contains infrequent reports of neuroendocrine carcinoma during pregnancy. The chemotherapy for this type of malignancy can cause severe nausea and neutropenia. We used recently developed modalities to ameliorate these side effects. CASE: A 22-year-old woman, gravida 4, para 2-0-1-2, presented at 24 weeks' gestation with a complaint of massive lower-extremity edema. Computed tomography scan delineated a large retroperitoneal mass. Biopsy of a small neck mass revealed a poorly differentiated neuroblastoma. A multidisciplinary approach to therapy was undertaken. The patient received cisplatin and etoposide chemotherapy. Complications of the first course included severe neutropenia and nausea with vomiting. Filgrastim and ondansetron were used to treat these complications. She delivered an 1825-g healthy male by cesarean for fetal distress at 35 weeks. No anomalies were noted at birth. Neonatal hematologic indices were normal CONCLUSION: A multidisciplinary approach to rare malignancies is warranted in pregnancy. Filgrastim and ondansetron are effective agents in the treatment of chemotherapy-associated complications. Their use in pregnancy warrants further investigations.

Adult↗
PubMed1993

Variation in body fat distribution and breast cancer risk in the families of patients with breast cancer and control families.

BACKGROUND: The pattern of body fat distribution in women has been correlated with the risk of developing breast and endometrial cancer. The authors determined whether body fat distribution varied between first-degree relatives of patients with breast cancer and in cancer-free families by comparing the body fat distribution of first-degree relatives of patients with breast cancer with age and Quetelet Index-matched controls. METHODS: Fifty-six first-degree relatives of newly diagnosed patients with breast cancer were compared with 56 controls (non-cancer family members) matched for age and Quetelet Index and were studied for variation in body fat distribution. Anthropometric measurements were taken for the abdomen, thigh, suprailiac, subscapular, biceps, and triceps skinfold thickness; waist and hip circumference; weight; and height. The distribution of body measurements and derived ratios in both case and control family members were compared using the Student t test. RESULTS: A significant variation in body fat distribution occurred among first-degree relatives in breast cancer and control families. In families with a history of breast cancer, first-degree family members were found to have significantly greater waist:hip ratio (P < 0.001) compared with controls without family history matched for age and Quetelet Index. Other variables indicating upper body fat localization, such as abdomen and suprailiac skinfold were significantly greater in family members of patients with breast cancer compared with controls. CONCLUSIONS: A marked variation occurred in body fat localization among first-degree relatives of patients with breast cancer and in cancer-free families. This finding implies a variation in breast cancer risk in these families. Identifying family members with upper body fat distribution in breast cancer families would allow targeting of these individuals for energetic screening and risk factor reduction interventions.

Adipose Tissue↗
PubMed1993

Decision analysis of hematopoietic growth factor use in patients receiving cancer chemotherapy.

BACKGROUND: Hematopoietic growth factors (HGFs) have been shown to reduce the incidence of neutropenia and fever in patients receiving cancer chemotherapy. PURPOSE: This cost analysis was designed to determine the conditions in which use of HGFs in patients receiving cancer chemotherapy is cost-effective. METHODS: We used a standard model based on decision theory; the model assumes that all patients experiencing neutropenia and fever will be hospitalized and treated with intravenous antibiotics. Data from a prospective, randomized clinical trial of granulocyte colony-stimulating factor in small-cell lung cancer treated with combination chemotherapy were used to determine baseline probabilities for control hospitalization risk and survival; proportional hospitalization risk with prophylactic HGF; and median durations of hospitalization and prophylactic HGF use. The model was analyzed by one-way and multivariate sensitivity analyses, with estimation of threshold values at which the expected cost is the same for either of two treatment options. One or more of the specific costs and durations and the probability for each group of threshold curves were varied in a sensitivity analysis that generated variable thresholds. Use of Monte Carlo analysis based on the available distributions of the main variables provided 90% confidence limits and an inference method for comparing decision options. RESULTS: The expected excess cost per treatment cycle, based on hospitalization for neutropenic fever and/or HGF administration, was $5500 for no HGF, $4750 for prophylactic HGF, and $6875 for therapeutic HGF. Sensitivity analysis provided the following thresholds for no HGF versus prophylactic HGF: control risk of hospitalization, 0.40; risk of hospitalization with HGF as a proportion of control, 0.64; total daily cost of hospitalization, $727; total daily cost of HGF, $344; duration of hospitalization, 7.3 days; and duration of HGF use, 11.0 days. Multivariate analysis revealed that conditions favoring the use of HGF on a cost basis become greater (a) as risk of hospitalization, total daily hospital cost, and duration of hospitalization increase and (b) as the proportional risk of hospitalization with HGF, daily cost of HGF, and duration of HGF treatment decrease. CONCLUSIONS: The major determinants of total excess cost were the control risk of hospitalization, the proportional reduction in risk with HGF, and the average daily hospital cost. IMPLICATIONS: Use of HGFs should be based on the risk of hospitalization for neutropenic fever and consideration of the patient population and institutional costs.

Colony-Stimulating Factors↗
PubMed1993

The anatomy of missed breast cancers.

Missed breast cancer continues to account for the highest percentage of medical malpractice cases in the United States. A retrospective, computer-aided study was performed to investigate the mechanisms of missed breast carcinomas, missed either by mammography or by clinical exam. In a consecutive series of 509 breast cancers found in patients registered at a University Comprehensive Breast Cancer Clinic, no tumour that was 5 mm or less in maximal diameter was clinically palpable. This subgroup consisted of seven in situ and 32 invasive carcinomas. The incidence of palpable tumours in 5 mm increments increased so that when a tumour was between 11 and 15 mm in size, 48% of the lesions were palpable, and with tumours greater than 20 mm in size, 84% were palpable. There was a good correlation between size of the tumour as judged by mammography and the eventual size determined by histologic examination. Smaller breast cancers were detected by mammography than by physical examination. In a separate analysis of 553 consecutive cases of breast cancer examined by mammography, there were 50 (9%) cases in which the cancer was not read from the mammogram. In retrospect, 10 of these mammograms were abnormal for a misinterpretation rate of 1.8%. Cancers associated with false negative mammograms occurred more often in younger women and in dense breast parenchyma than cancers detected by mammography. Cancers missed by mammography were smaller than palpable cancers detected by mammography, more often had negative nodes and presented with a lower stage of disease. Breast augmentation implants were associated more frequently with missed breast cancers, with 5/8 clinically detected breast carcinomas being undetected by mammography. An asymmetric mass was more often associated with cancers missed by mammography, accounting for the sole sign of malignancy in 3% of all cancers, but was the source of 14% of false negative exams. Architectural distortion, ill-defined or well circumscribed masses or calcifications as mammographic signs of malignancy were not associated with an increased frequency of missed cancers. Three 'interval' breast cancers occurred in this series and are included in the false negative mammograms. It is concluded that the threshold of clinically detected breast cancers is 6 mm and experienced clinicians do not detect the majority of breast cancers until the lesions are greater than 16 mm. Mammography has a defined misinterpretation and false negative rate. Likewise, asymmetric mammographic densities that are greater than 16 mm and are not palpable may be followed, since most breast cancers are palpable in this range.

Adult↗
PubMed1993

Cost-effectiveness of white cell-reduction filters in treatment of adult acute myelogenous leukemia.

The objective of this study was to compare the cost and cost-effectiveness of three transfusion strategies in the treatment of acute myelogenous leukemia: 1) the use of unfiltered pooled platelets until alloimmunization developed and of crossmatch-compatible single-donor platelets thereafter; 2) the use of filtered blood components until alloimmunization occurred and of crossmatch-compatible single-donor platelets thereafter; and 3) the use of single-donor platelets from the beginning. The data sources were English language articles on transfusion medicine in acute leukemia and the management of acute leukemia and review of the transfusion experience at the H. Lee Moffitt Cancer Center. The method was decision analysis with a software program for cost-effectiveness, sensitivity analysis, threshold evaluation, and Monte Carlo sensitivity analysis. In the basic models, the total costs of the first, second, and third strategies are, respectively, $12,557.14, $11,406.17, and $13,016.16 without bone marrow transplant and $14,002.72, $12,281.89, and $13,727.48 with bone marrow transplant. The threshold between the first and second strategies in regard to risk of refractoriness to filtered blood components and pooled platelets was 0.30 and 0.27, respectively, without bone marrow transplant and 0.28 and 0.40 with bone marrow transplant. According to a Monte Carlo sensitivity analysis of 500 samples, the second strategy is more cost-effective than the first in 76 percent of cases. It is concluded that the use of filtered blood components is unlikely to increase the cost of treatment.

Blood Component Transfusion↗
PubMed1993

Overestimation of test effects in clinical judgment.

The purpose of this study was to assess the ability of health care professionals to evaluate the effect of test results on disease risk. Fifty health care professionals, including 29 physicians and 21 nonphysicians, associated with a university hospital were studied. Subjects were presented with two hypothetical scenarios involving a common clinical situation to assess the effect of test results on the estimation of disease risk. Estimates of the pretest and posttest probability of breast cancer and mammography sensitivity and specificity were elicited for hypothetical 30- and 70-year-old patients presenting with a breast lump. There was no significant difference between physician and nonphysician probability and sensitivity estimates, although physicians provided higher specificity estimates which were more consistent with literature-derived values. Both physicians and nonphysicians consistently overestimated the risk associated with a positive test result compared to probabilities derived from Bayes' theorem based on the subject's pretest probability and sensitivity and specificity estimates, as well as standard test performance estimates. There was no significant difference between posttest probability estimates for negative test results and those derived from Bayes' theorem utilizing the subject's pretest probability and sensitivity and specificity estimates. Physicians and nonphysicians both estimate test performance characteristics accurately but consistently overestimate the effect of positive test results on the probability of disease. In addition to experience with specific clinical problems, decision making by clinicians could be enhanced by training in the formal methods of decision analysis.

Adult↗
PubMed1992

Environmental tobacco smoke and lung cancer risk in nonsmoking women.

BACKGROUND: Exposure to environmental tobacco smoke (passive smoking) has been suggested to be a cause of lung cancer, although early epidemiologic studies have produced inconsistent results. PURPOSE: We conducted an epidemiologic case-control study to assess the relationship between exposure to environmental tobacco smoke and lung cancer risk among women who have never smoked (i.e., having smoked for a total of less than 6 months or having smoked less than 100 cigarettes in their lifetimes). METHODS: Case patients (n = 210) were women with histologically confirmed primary carcinomas of the lung who were lifetime nonsmokers. They were identified through hospital tumor registries and the Florida Cancer Data System of the Statewide Cancer Registry. Community-based control women (n = 301) were also lifetime nonsmokers and were identified through random-digit dialing. Details on childhood and adulthood exposures to environmental tobacco smoke were ascertained through interviews with the study participants themselves or with surrogate respondents. Risks were calculated in terms of smoke-years, defined as the sum of the reported years of exposure to cigarette smoke from each smoker in the household. RESULTS: The risk of lung cancer more than doubled for women who reported 40 or more smoke-years of household exposure during adulthood (odds ratio [OR] = 2.4; 95% confidence interval [CI] = 1.1-5.3) or 22 or more smoke-years of exposure during childhood and adolescence (OR = 2.4; 95% CI = 1.1-5.4). Risks were highest for non-adenocarcinoma lung cancers, although modest elevations in risk were also observed for adenocarcinomas. When a surrogate respondent other than the patient's husband provided information on exposure, the risk estimates were considerably lower. CONCLUSION: These findings suggest that long-term exposure to environmental tobacco smoke increases the risk of lung cancer in women who have never smoked.

Adenocarcinoma↗
PubMed1992

Risk factors for cancer.

It is no longer reasonable to divide cancers into those that are genetic in origin and those that are environmental in origin. With rare exception, carcinogenesis involves environmental factors that directly or indirectly exert a change in the cell's genome. Virtually all causes of cancer are multifactorial, sometimes involving an inherited predisposition to the carcinogenic effects of environmental factors, which include chemicals, ionizing radiation, and oncogenic virus. Carcinogenesis is a multistep process including induction, promotion, and progression. Initiation requires an irreversible change in the cellular genome, whereas promotion is commonly associated with prolonged and reversible exposure. Tumor progression results in genotypic and phenotypic changes associated with tumor growth, invasion, and metastasis. Most information on human cancer risk is based on epidemiologic studies involving both exposed and unexposed individuals. The quality of such studies depends on their ability to assess the strength of any association of exposure and disease and careful attention to any potential bias. Few cancers are inherited in a Mendelian fashion. Several preneoplastic conditions, however, are clearly inherited and several malignancies demonstrate weak familial patterns. Environmental factors may exert their effect on DNA in a random fashion, but certain consistent changes, including specific translocations of genetic information, are often found. Currently, there is great interest in the close proximity of certain oncogenes governing growth control to the consistent chromosomal changes observed. Such changes may represent a final common pathway of action for environmental carcinogens. Sufficient laboratory and epidemiologic evidence exists to establish a causal association of several chemical agents with cancer. The most important carcinogenic chemicals are associated with life-style factors, whereas agents related to other environmental, occupational, or medical exposure are numerically less important. Most chemical agents exert their carcinogenic effects as electrophilic reactants covalently binding to DNA. Certain agents such as asbestos are carcinogenic by virtue of their physical properties. Several short-term tests have been used to screen for chemical carcinogens. Whole-animal studies remain the standard for predicting carcinogen risk in humans, although major limitations in such studies exist. Ionizing radiation also exerts its carcinogenic effect through damage to cellular macromolecules including DNA. Excess cancer risk appears after a latent period of several years following exposure. Risk increases in approximately a linear fashion in proportion to the radiation energy, cumulative dose, and a variety of host biologic factors. The greatest source of average radiation exposure to the US population is from the uranium decay product radon.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗