Benzene and the dose-related incidence of hematologic neoplasms in China. Chinese Academy of Preventive Medicine--National Cancer Institute Benzene Study Group

BACKGROUND

Benzene is a widely distributed environmental contaminant known to cause leukemia, particularly acute nonlymphocytic leukemia, and perhaps other hematologic neoplasms and disorders. Few epidemiologic studies, however, have been able to address relationships between the extent of benzene exposure and the level of risk.

PURPOSE

A large cohort study was carried out in China to evaluate the risks of developing specific hematologic neoplasms and selected related disorders in relationship to quantitative estimates of occupational benzene exposure.

METHODS

A cohort of 74828 benzene-exposed and 35805 unexposed workers employed from 1972 through 1987 in 12 cities in China was identified and followed to determine the incidence of hematologic neoplasms and related disorders. Estimates of benzene exposure were derived from work histories and available historic benzene measurements. Existing pathologic material and supporting medical records were reviewed to establish diagnoses of disease. Relative risks (RRs) (i.e., ratios of incidence rates for specific hematologic neoplasms and related disorders in the benzene-exposed group to incidence rates in the unexposed group) were determined by use of Poisson regression analysis, with stratification by age and sex.

RESULTS

For workers historically exposed to benzene at average levels of less than 10 parts per million (ppm), the RR for all hematologic neoplasm combined was 2.2 (95% confidence interval [CI] = 1.1-4.2), and, for the combination of acute nonlymphocytic leukemia and related myelodysplastic syndromes, the RR was 3.2 (95% CI = 1.0-10.1). For individuals who were occupationally exposed to benzene at constant levels of 25 ppm or more, the RR for the combination of acute nonlymphocytic leukemia and related myelodysplastic syndromes was 7.1 (95% CI = 2.1-23.7). Workers with 10 or more years of benzene exposure had an RR of developing non-Hodgkin's lymphoma of 4.2 (95% CI = 1.1-15.9), and the development of this neoplasm was linked most strongly to exposure that had occurred at least 10 years before diagnosis (i.e., distant exposure) (P for trend = .005, two-sided). In contrast, the risk for the combination of acute nonlymphocytic leukemia and related myelodysplastic syndromes was significantly increased among those with more recent benzene exposure (P for trend = .003, two-sided), but it was not linked to distant exposure (P for trend = .51, two-sided).

CONCLUSIONS

The results of this study suggest that benzene exposure is associated with a spectrum of hematologic neoplasms and related disorders in humans. Risks for these conditions are elevated at average benzene-exposure levels of less than 10 ppm and show a tendency, although not a strong one, to rise with increasing levels of exposure. The temporal pattern of benzene exposure appears to be important in determining the risk of developing specific diseases.

[Gaze-position-dependent activities of striate cortex (V1) neurones of awake macaque monkeys]

We recorded the activities of single neurons of the primary visual cortex in awake, behaving monkeys to test the influence of the position of gaze on cellular activity. Two monkeys (Macaca mulatta) were trained to fixate a small spot positioned sequentially at 25 locations on a viewing screen. About half (52%) of the neurons recorded showed a selective gaze field (GF), when monkey fixated at this field of view, the cell activities increased significantly. For the majority of the neurons, GF located at the contralateral field of view with respect to the hemisphere from which responses were recorded. The GF was usually found a few degrees peripheral to the related RF. Gaze-position-dependent neurons were found at different depths of the cortex, but mostly in the superficial and the deepest layers. The results indicate that the striate cortex neurons may code information about gaze position.

Clinical correlations of immunophenotypic variations and the presence of trisomy 12 in B-cell chronic lymphocytic leukemia

In a prospective study of 93 consecutive untreated patients with B-cell chronic lymphocytic leukemia, we examined the clinical relevance of surface immunoglobulin (sIg) heavy chain (HC) and light chain (LC) isotypes, CD11c or CD25 expression, and the presence of trisomy 12 by fluorescence in situ hybridization (FISH). Careful morphologic evaluation was performed to exclude patients with other forms of chronic lymphoid leukemias, including mantle cell lymphoma, prolymphocytic leukemia, and leukemia phase of lymphoma. In addition, clonally restricted sIg and CD5 surface determinant were expressed in all patients. Clinical presentation, including blood cell counts, clinical stage, and organomegaly, did not correlate with any of the measured variables. After a median follow-up period of 3 years, the particular HC or LC isotype or CD11c expression did not correlate with either disease progression or treatment-free survival. However, trisomy 12 and CD25 expressions were both associated with accelerated disease progression and a shorter treatment-free survival time. Our results confirm the adverse prognostic significance of trisomy 12 expression in chronic lymphocytic leukemia and suggest that CD25 expression may have an unfavorable clinical impact.

Predictive capacity of the International Prognostic Factor Index in patients with peripheral T-cell lymphoma

PURPOSE

The International Prognostic Factor Index has been shown to predict the outcome of patients with predominantly B-cell lymphomas classified using traditional classifications, including the Working Formulation, but its prognostic importance has not been tested in a cohort of patients with exclusively T-cell lymphomas. This study was conducted to evaluate the prognostic significance of the International Prognostic Factor Index in patients with peripheral T-cell lymphoma (PTCL).

PATIENTS AND METHODS

Seventy-eight patients (48 men and 30 women) with PTCL seen at a single institution between 1985 and 1995 were included in the analysis. The morphology and immunocytochemistry of all the original biopsy specimens were reviewed by a single pathologist and classified using the Revised European-American Lymphoma (REAL) classification. The International Prognostic Factor Index, as well as clinical and biochemical parameters, were evaluated by univariate and multivariate analyses to determine their association with patient outcome.

RESULTS

The International Prognostic Factor Index strongly predicted survival when all patients were included in the analysis (P < .001). For patients < or = 60 years, the age-adjusted International Index significantly predicted long-term survival (P = .0218). For patients older than 60 years, the age-adjusted International Index also significantly predicted survival (P = .002). Liver involvement (P = .006) and bone marrow involvement (P = .014) were also significant prognostic factors in the univariate analysis, but only the International Index remained significant in the multivariate analysis (P = .001).

CONCLUSION

The International Prognostic Factor Index, which significantly predicts outcome in patients with aggressive/intermediate-grade B-cell lymphomas, has similar prognostic importance in patients with PTCL.

[Effects of fructus cnidii coumarins compared with nilestriol on osteoporosis in ovariectomized rats]

AIM

To compare the total coumarins from dried fruits of Cnidium monnieri (TCCM) and nilestriol (Nil) against osteoporosis.

METHODS

SD rats (40, female, 3-month-old) were randomly divided into basal control, age control, ovariectomized (Ova), Ova + TCCM 67 mg.kg-1, Ova + TCCM 200 mg.kg-1, 6 times a week, and Ova + Nil 1 mg.kg-1, i.g. once a week. After 12 wk, sections (20 microns) of proximal tibiae were examined histologically.

RESULTS

Ova reduced markedly the trabecular bone mass due to bone resorption excessed bone formation (% Tb. Ar -59%). Treatment with TCCM 67 mg.kg-1 partly suppressed bone turnover, but did not inhibit bone loss in Ova rats (% Tb.Ar -43%). Treatment with TCCM 200 mg.kg-1 and Nil 1 mg.kg-1 increased the trabecular area (% Tb. Ar +100% and +274%).

CONCLUSION

Nil was more potent than TCCM in protecting against osteoporosis in Ova rats via supression of bone turnover.

Eye position-dependent activation of neurones in striate cortex of macaque

Extracellular recordings were made in the striate cortex in awake, behaving monkeys to test the influence of the eye position on cellular activity. Two monkeys (Macaca mulatta) were trained to fixate a small spot at 25 different eye positions. About half (52%) of the studied neurones showed a selective gaze field (GF). The cells' activities increased significantly when the monkey fixated at this field of view. For the majority of these neurones, GFs were located at the contralateral field of view with respect to the hemisphere from which responses were recorded, and were usually found a few degrees peripheral to the related receptive field. Eye position-dependent neurones were found at different depths of cortex, but mostly in the superficial layers. The results indicate that some neurones in striate cortex may code information about eye position and could contribute to target localization in a head-centred coordinate system by combining retinal and afferent eye position signals.

Abrogation of p53 function by HPV16 E6 gene delays apoptosis and enhances mutagenesis but does not alter radiosensitivity in TK6 human lymphoblast cells

In order to gain a better understanding of the role of p53 in radiation-induced mitotic failure, apoptosis and mutagenesis, we introduced the HPV16 E6 gene via a retroviral vector into the TK6 human lymphoblast cell line which expresses wild type p53. Abrogation of p53 function by E6 resulted in a delayed and reduced apoptotic response and a moderate increase in the frequency of mutations at the thymidine kinase (tk) locus following gamma-irradiation, but failed to alter radiosensitivity. The apoptotic response of the E6-transduced line was intermediate between that of wild type TK6 and the WTK1 cell line. WTK1 is derived from the same parental cell line as TK6 but expresses mutant p53. The spontaneous and gamma-ray-induced mutation frequencies in E6-transduced TK6 cells, although higher than that of the parental TK6 cell line, were still much lower than that of the WTK1 line. No effect on apoptosis, radiosensitivity or mutability was observed when the HPV16 E6 gene was introduced into the WTK1 cells. These results indicate that p53 does not regulate the radiosensitivity of TK6 cells through the apoptotic pathway. Furthermore, the previously observed enhanced radioresistance and mutability in WTK1 cells must be attributed to a more complex mechanism than p53 status alone.

Useful panel of antibodies for the classification of acute leukemia by immunohistochemical methods in bone marrow trephine biopsy specimens

To evaluate the feasibility of acute leukemia typing on routinely processed bone marrow biopsy specimens, 72 cases of previously established acute leukemia covering the spectrum of 17 known subtypes were studied immunohistochemically. Most leukemic myeloblasts were positive for myeloperoxidase in 16 (84%) of 19 cases of acute myeloid leukemia, M1-M4, and M6. Most leukemic cells in 11 of 12 M4 and M5 cases were positive for CD68 (PG-M1). All six M6 cases stained with hemoglobin. Leukemic megakaryoblasts in three of four M7 cases were positive for factor VIII-related antigen. Almost all leukemic cells of 8 T-lineage acute lymphoblastic leukemia (ALL) and 19 B-lineage ALL cases were positive for CD3 and CD79a (HM57), respectively. Staining with CD20 (L26) was positive in the more differentiated B-lineage ALL cases and strongest in L3. Immunohistochemical typing of acute leukemia is possible for most types using this panel of cell lineage-specific antibodies.

Field programmable gate array in a fast 256-channel data acquisition system

We describe an FPGA (Field Programmable Gate Array) controlled fast data acquisition system with 256 channels suitable for high resolution electrocardiographic (ECG), electrogastrographic (EGG) and late potential (LP) recordings. The A/D converter provides 800ns conversion time with 12 bits. The S11W, a 16 bit, parallel, I/O interface, is used to connect the data acquisition device to a portable SPARC-compatible computer. With only one A/D converter, we have achieved 2 kHz sampling rate for each channel and more than 1MB/s overall by using an overlapping delay technique. Channel parameters can be selected independently from one of eight gains ranging from 50 to 10,000, and one of three filters ("ECG" 0.05-120Hz, "EGG" 0.001-1Hz and "LP" 60-1kHz). There are eight programmable sampling frequencies from 2Hz to 2kHz. The system is fully battery operated and protected from the defibrillation high voltages to meet the safety requirements. The acquisition system can be widely used in medical research and clinical applications.

Patterns of recovery in the Guillain-Barre syndromes

Clinical, electrodiagnostic, and pathologic studies indicate that the Guillain-Barre syndromes (GBSs) include both primary demyelinating and primary axonal forms. The axonal forms are usually thought to have a poorer prognosis, with less chance for rapid or complete recovery. In northern China, epidemics of one axonal form, acute motor axonal neuropathy (AMAN), occur annually in the summer. Autopsy studies in some fatal cases have demonstrated wallerian-like degeneration of motor roots and motor fibers in the peripheral nerves. Recovery of such patients would require axonal regeneration along the entire length of the nerve fiber. In a 2-year prospective study of GBS at a single hospital in northern China, 42 patients were classified as having either AMAN (32 patients), acute inflammatory demyelinating polyneuropathy (AIDP) (8 patients), or as undetermined (2 patients) by electrodiagnostic criteria. Their recoveries were monitored clinically. The recovery times of AMAN and AIDP patients were similar: the median time to regain the ability to walk 5 meters with assistance was 31 days for patients classified as having AMAN and 32 days for those classified as having AIDP. These rapid recovery times are incompatible with severe wallerian degeneration of the ventral roots and motor nerve fibers. The rapid recoveries observed in AMAN patients could be explained by relatively quickly reversible immune-mediated changes at nodes of Ranvier in motor fibers, by degeneration and regeneration of intramuscular motor nerve terminals, or both.

Bone marrow granulomas associated with chronic natural killer cell lymphocytosis

Two patients with chronic natural killer cell lymphocytosis (CNKL) and associated bone marrow granulomas (BMGs) are described. The increases in the peripheral blood of both the proportion (64 and 74%) and absolute number (2,000/microL and 4,700/microL) of NK cells have persisted for more than 1 and 3 years. One patient was asymptomatic with thrombocytopenia and neutropenia, and the other presented with fever of unidentified origin, which has since responded to a nonsteroidal anti-inflammatory agent. Bone marrow examination in both patients showed loose aggregates of epithelioid histiocytes similar to the noncaseating granulomas seen in other diseases. An unusual feature, however, was the presence of many scattered, large mononuclear histiocytes that were morphologically similar to atypical megakaryocytes. Extensive clinical and laboratory studies did not reveal an established cause for the BMGs. BMGs may be associated with CNKL, with the unusual feature of scattered, atypical mononuclear histiocytes.

The lost endotracheal tube--a rare complication of accidental esophageal intubation

Endotracheal intubation is a discreet skill for the management of compromised airway. Various complications associated with this procedure have been described. Here, we would like to present a pediatric patient suffering from cerebellar atrophy, who was intubated in a local clinic due to seizure with cyanosis and loss of consciousness. Unfortunately, due to inadvertent esophageal intubation and bad management, the patient swallowed the endotracheal tube together with two detached loose teeth. This irrational and iatrogenic medical misconduct as exemplified in this accident calls forth the need of educating and disciplining the nonanesthetic physicians for acute management of airway, particularly of those who would likely come across difficult airway problems.

Residential exposure to 60-Hertz magnetic fields and adult cancers in Taiwan

We conducted a case-control study, using matching on date of birth, sex, and date of diagnosis, in northern Taiwan to evaluate the risks of adult leukemia, brain tumors, and female breast cancers in relation to residential exposure to 60-Hertz (Hz) magnetic fields. Cases were persons with newly diagnosed cancers reported to the cancer registry between 1987 and 1992, and controls were persons with cancers sites other than those previously suspected of being associated with magnetic fields. Magnetic fields in the residences occupied by the study subjects at the time of diagnosis were estimated from high-voltage transmission lines. The results were based on the separate analysis of 870 cases of leukemia, 577 brain tumors, and 1,980 female breast cancers. We estimated the risk of leukemia among those exposed to magnetic fields of > 0.2 microtesla (microT), relative to the risk among those exposed to fields of < 0.1 microT; the odds ratio was 1.4 [95% confidence interval (CI) = 1.0-1.9]. For distance < 50 meters relative to > or = 100 meters, the relative risk was 2.0 (95% CI = 1.4-2.9). For brain tumors and female breast cancers, the odds ratios were close to unity.

Mortality among benzene-exposed workers in China

A large cohort of 74,828 benzene-exposed and 35,805 nonexposed workers employed between 1972 and 1987 in 12 cities in China was followed to determine mortality from all causes. Benzene-exposed study subjects were employed in a variety of occupations including coating applications, and rubber, chemical, and shoe production. Mortality was slightly increased among workers with greater cumulative exposure to benzene (ptrend < 0.05), but this excess was largely due to cancer deaths (ptrend < 0.01). Deaths due to lymphatic and hematopoietic malignancies (ptrend = 0.01) and lung cancer (ptrend = 0.01) increased with increasing cumulative exposure to benzene. Investigations continue to relate benzene exposure to specific lymphatic and hematopoietic malignancies and other causes of death.

Clinical features of hematopoietic malignancies and related disorders among benzene-exposed workers in China. Benzene Study Group

Previous occupational cohort studies of benzene-exposed workers have for the most part used only death certificates to validate diagnoses of workers developing leukemia and other hematopoietic and lymphoproliferative malignancies and related disorders (HLD). In a follow-up study of 74,828 benzene-exposed workers and a comparison group of 35,805 nonexposed workers from 12 cities in China, we sought to characterized clinicopathologically and to confirm diagnoses of all cases of HLD. Using medical records, laboratory hematology results, and histopathology, U.S. and Chinese expert hematopathologists, blinded to exposure status, carried out a detailed review using standardized evaluation forms. Key among the findings were a notable diversity of malignant and nonneoplastic hematopoietic and lymphoproliferative disorders, documentation of excess myelodysplastic syndromes among benzene workers, and widespread dyspoiesis involving all hematopoietic cell lines. As sophisticated clinicopathologic characterization and corresponding classification schemes for HLD become increasingly widespread, it is recommended that future epidemiologic investigations of benzene workers incorporate similarly detailed morphologic evaluation. In extending follow-up of this cohort of young workers, we will continue to use all available clinical, laboratory hematology, and pathology data as well as cytogenetic and biochemical markers to characterized various HLD outcomes. These careful surveillance mechanisms should also provide additional insight into carcinogenic mechanisms of benzene and allow comparison of the molecular pathogenesis of HLD induced by benzene versus chemotherapy, radiation, or other exposure.

Heterogeneity and clinical relevance of the intensity of CD20 and immunoglobulin light-chain expression in B-cell chronic lymphocytic leukemia

In a prospective study, peripheral lymphocytes of 93 previously untreated patients with B-cell chronic lymphocytic leukemia (B-CLL) were evaluated with flow cytometry for the intensity of CD20 and surface immunoglobulin (sIg) light-chain (LC) expression. Molecules of equivalent soluble fluorescence were used to classify intensity of surface antigen expression as "strong," "moderate," or "weak." Despite reproducible morphological consistency with B-CLL, variability in intensity of CD20 and sIg light chain expression was substantial. CD20 intensity was classified as weak in 62% of patients, moderate in 12%, and strong in 26%. Expression of sIg light chain was weak in 76% and strong in 24%. The patients were followed up for a median of 3.1 years. Intensity of expression of CD20 and sIg light chain was not correlated with any presenting feature at the time of phenotyping, including clinical stage and degree of lymphocytosis or organomegaly. Similarly, clinical course of the disease, time to progression, response to therapy, and overall and treatment-free survival were not predictable from the intensity of CD20 or sIg light chain expression. In conclusion, bright expression of CD20 or sIg light chain is not an unusual feature in B-CLL and may not influence clinical presentation or short-term prognosis.

The premortem recognition of systemic senile amyloidosis with cardiac involvement

PURPOSE

To recognize systemic senile amyloidosis involving the heart and to determine outcome.

PATIENTS AND METHODS

All patients with the diagnosis of amyloidosis at the Mayo Clinic from January 1, 1984 through May 1, 1992, were reviewed. Amyloid was confirmed histologically by sulfated alcian blue and alkaline Congo red staining. The labeled streptavidin-biotin immunoperoxidase method was used with antisera against A kappa, A lambda, AA, transthyretin, and beta 2-microglobulin. Anti-P-component and antisera to albumin were used as controls. Chest radiographs, electrocardiograms, transthoracic echocardiograms, and cardiac catheterization data of all patients were reviewed. Serum and urine were examined with immunoelectrophoresis and immunofixation for the presence of a monoclonal protein. Lymphocyte DNA was examined for transthyretin mutations associated with familial amyloidosis.

RESULTS

We identified 18 patients with myocardial tissue that stained positive for amyloid with sulfated alcian blue and Congo red and with transthyretin antisera. Congestive heart failure was present at diagnosis in 17 of the 18 patients. Atrial fibrillation was found in 11 patients. No monoclonal protein was found in the serum or urine. The echocardiographic findings were consistent with infiltrative cardiomyopathy due to amyloidosis in 16 patients. Right heart pressures were elevated in all 7 patients who had right-side heart catheterization. No transthyretin mutations were found in the leukocyte DNA from 12 patients. The actuarial median survival was 5 years; in contrast, the median survival was 5.4 months in 147 patients with primary amyloidosis (AL) who presented with congestive heart failure.

CONCLUSION

Patients with cardiac amyloid and no monoclonal protein in the serum or urine must have immunohistochemical staining for kappa and lambda light chains and transthyretin to distinguish between systemic senile amyloidosis, familial amyloidosis, and AL. Patients with systemic senile amyloidosis should not be treated with alkylating agents. Their survival is much longer than that of patients with AL (60 versus 5.4 months).

Acute motor axonal neuropathy: an antibody-mediated attack on axolemma

The acute motor axonal neuropathy (AMAN) form of the Guillain-Barre syndrome is a paralytic disorder of abrupt onset characterized pathologically by motor nerve fiber degeneration of variable severity and by sparing of sensory fibers. There is little demyelination or lymphocytic inflammation. Most cases have antecedent infection with Campylobacter jejuni and many have antibodies directed toward GM1 ganglioside-like epitopes, but the mechanism of nerve-fiber injury has not been defined. In 7 fatal cases of AMAN, immunocytochemistry demonstrated the presence of IgG and the complement activation product C3d bound to the axolemma of motor fibers. The most frequently involved site was the nodal axolemma, but in more severe cases IgG and C3d were found within the periaxonal space of the myelinated internodes, bound to the outer surface of the motor axon. These results suggest that AMAN is a novel disorder caused by an antibody- and complement-mediated attack on the axolemma of motor fibers.

Experimental Campylobacter jejuni infection in the chicken: an animal model of axonal Guillain-Barré syndrome

OBJECTIVE

To develop and characterise an animal model of paralytic neuropathy after Campylobacter jejuni infection. Campylobacter infection precedes development of many cases of Guillain-Barré syndrome and is particularly associated with cases having prominent axonal degeneration. Understanding the pathogenesis of Guillain-Barré syndrome after C jejuni infection has been slowed by the lack of animal models.

METHODS

A spontaneous paralytic neuropathy is described that developed in chickens from the farms of four patients with Guillain-Barré syndrome. The production of paralytic neuropathy in chickens experimentally fed Campylobacter jejuni isolated from one of these patients is reported. The sciatic nerves of the spontaneously paralysed chickens were examined pathologically in teased fibres, in plastic embedded sections, and by electron microscopy. Two large groups of chickens were then fed cultures of a C jejuni (Penner type O:19) isolated from one of these patients.

RESULTS

The chickens with spontaneous paralysis had pathologically noninflammatory neuropathy. Pathology in the sciatic nerves ranged from no detectable changes to severe Wallerian-like degeneration. In the experimentally inoculated groups, an average of 33% of the chickens became paralysed. The median time after inoculation to paralysis was 12 days. The lesions found in the first few days of paralysis included nodal lengthening and paranodal demyelination. In those animals that survived for several days after onset of weakness, the pathology was dominated by extensive Wallerian-like degeneration. Animals that survived for weeks with no clinically apparent neuropathy had paranodal remyelination in some teased nerve fibres, reflecting earlier paranodal demyelination.

CONCLUSION

Experimental inoculation with C jejuni may provide a new model for understanding some forms of Guillain-Barré syndrome.

Estimation of the optimal concentrations of residual sugar and cell growth rate for a fed-batch culture of Saccharomyces cerevisiae

Estimation of the optimal concentrations of residual sugar in medium for a fed-batch culture of Baker's yeast has been studied and practiced. The concentrations, however, depended on different species and targets of the biomass, which was expected to be made. Kinetic changes of the residual phosphate salt in the medium conformed to a logarithmic process until the fourth hour during an 11-h culture. The parabolic method (see ref. 9 later in article) might be qualified to maintain the concentrations of residual sugar around 0.15 g/L. It was demonstrated that cell growth followed a sigmoid process during a fed-batch culture, because the cells consumed the nutrient with two metabolic pathways, one was for cell conversion and another was for non-cell conversion. With the parabolic method, we can estimate kinetics of cell growth and cell growth rate during the culture.

Abrogation of P53 function by transfection of HPV16 E6 gene does not enhance resistance of human tumour cells to ionizing radiation

Suppression of wild-type p53 expression has been shown to enhance the radiation resistance of human diploid fibroblasts, but results concerning the role of p53 expression in the sensitivity of human tumour cells have been conflicting. In order to address this question, we transfected four human tumour cell lines with the human papilloma virus 16 E6 gene and compared the radiosensitivity of subclones expressing E6 with that of subclones transfected with the neo gene alone. E6 binds to wild-type p53 promoting its degradation and abrogating its function. Two of these cell lines, one derived from a squamous cell carcinoma and the other an osteogenic sarcoma, expressed wild-type p53. The other two cell lines were of similar origins and histologies but expressed mutant or no p53 (null). Insertion of E6 into the cell was accomplished by two techniques: (1) to-transfection of plasmid vectors containing neo and E6; (2) infection with a retroviral vector containing neo and E6. Multiple transfected subclones were examined for each cell line. Transfection with E6 and abrogation of p53 function had no significant influence on the radiosensitivity of any of the cell lines tested. In particular, there was no evidence that loss of wild-type p53 function increased the resistance of these human tumour cell lines to ionizing radiation.

Epidemiological appraisal of studies of residential exposure to power frequency magnetic fields and adult cancers

OBJECTIVES

To appraise epidemiological evidence of the purported association between residential exposure to power frequency magnetic fields and adult cancers.

METHODS

Literature review and epidemiological evaluation.

RESULTS

Seven epidemiological studies have been conducted on the risk of cancer among adults in relation to residential exposure to power frequency magnetic fields. Leukaemia was positively associated with magnetic fields in three case-control studies. The other two case-control studies and two cohort studies did not show such a link. Brain tumours and breast cancer have rarely been examined by these studies. Based on the epidemiological results, the analysis of the role of chance and bias, and the criteria for causal inferences, it seems that the evidence is not strong enough to support the putative causal relation between residential exposure to magnetic fields and adult leukaemia, brain tumours, or breast cancer. Inadequate statistical power is far more a concern than selection bias, information bias, and confounding in interpreting the results from these studies, and in explaining inconsistencies between studies.

CONCLUSIONS

Our reviews suggested that the only way to answer whether residential exposure to magnetic fields is capable of increasing the risks of adult cancers is to conduct more studies carefully avoiding methodological flaws, in particular small sample size. We also suggested that the risk of female breast cancer should be the object of additional investigations, and that future studies should attempt to include information on exposure to magnetic fields from workplaces as well as residential exposure to estimate the effects of overall exposure to magnetic fields.

Spectrum of diseases associated with increased proportions or absolute numbers of peripheral blood natural killer cells

In a retrospective review of 1501 lymphoid flow cytometric studies of peripheral blood, we identified an increased proportion of natural killer cells in 125 cases (8%), 49 (3%) of which had a concomitant increase in absolute number of natural killer cells. Of the latter, the most frequent associated disorder was chronic natural killer cell lymphocytosis. Substantial quantitative increases in natural killer cells were also observed in some patients with lymphoma, leukaemia, immune thrombocytopenic purpura, or myelodysplastic syndrome. Our study provides incidence figures and clinical associations of an increased number of natural killer cells in the peripheral blood.