Cigarette smoking and leukemia: results from the Lutheran Brotherhood Cohort Study

The importance of evaluating specific myeloid malignancies in epidemiological studies of environmental carcinogens

INTRODUCTION

Although myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), myeloproliferative neoplasms (MPN) - including chronic myeloid leukemia (CML) - and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) are largely clinically distinct myeloid malignancies, epidemiological studies rarely examine them separately and often combine them with lymphoid malignancies, limiting possible etiological interpretations for specific myeloid malignancies.

METHODS

We systematically evaluated the epidemiological literature on the four chemical agents (1,3-butadiene, formaldehyde, benzene, and tobacco smoking, excluding pharmaceutical, microbial and radioactive agents, and pesticides) classified by the International Agency for Research on Cancer as having sufficient epidemiological evidence to conclude that each causes "myeloid malignancies." Literature searches of IARC Monographs and PubMed identified 85 studies that we critically assessed, and for appropriate subsets, summarized results using meta-analysis.

RESULTS

Only two epidemiological studies on 1,3-butadiene were identified, but reported findings were inadequate to evaluate specific myeloid malignancies. Studies on formaldehyde reported results for AML and CML - and not for MDS or MPN - but reported no increased risks. For benzene, several specific myeloid malignancies were evaluated, with consistent associations reported with AML and MDS and mixed results for CML. Studies of tobacco smoking examined all major myeloid malignancies, demonstrating consistent relationships with AML, MDS and MPN, but not with CML.

CONCLUSIONS

Surprisingly few epidemiological studies present results for specific myeloid malignancies, and those identified were inconsistent across studies of the same exposure, as well as across chemical agents. This exercise illustrates that even for agents classified as having sufficient evidence of causing "myeloid malignancies," the epidemiological evidence for specific myeloid malignancies is generally limited and inconsistent. Future epidemiological studies should report findings for the specific myeloid malignancies, as combining them post hoc - where appropriate - always remains possible, whereas disaggregation may not. Furthermore, combining results across possibly discrete diseases reduces the chances of identifying important malignancy-specific causal associations.

Association of various risk factors with chronic lymphocytic leukemia and its cytogenetic characteristics

This study aimed to investigate whether occupational and environmental exposures, lifestyle, family, and medical history are associated with chronic lymphocytic leukemia (CLL) risk and its chromosomal abnormalities. The study included 138 CLL cases and 141 age- and sex-matched controls. Information data were collected through in-person interviews from cases and controls. Cytogenetic analysis was performed on CLL bone marrow cells. Positive associations were found between CLL and cancer family history, smoking, pneumonia, and exposure to petroleum, metals, pesticides/chemical fertilizers, detergents, and medical radiation. Chromosome deletions of 11q and 13q were more frequent in patients exposed to pesticides and rubber, respectively. This study investigated for the first time specific risk factors in relation to CLL aberrations and presented positive correlations. Moreover, it indicates the possible involvement of specific occupational and lifestyle risk factors in the onset of CLL.

Cigarette Smoking and Acute Leukemia

Recent cohort and case-control studies have suggested that cigarette smoking may be involved in the etiology of leukemia. Rising trends have been observed for all leukemias when the amount of cigarettes smoked increased. However, the magnitude of the trend was strongest for myeloid leukemia. Although no detailed biological mechanism has been proposed, a causal link is made plausible by evidence of systemic effects of cigarette smoke and the presence in cigarette smoke of chemicals (benzene) and radioactive substances that have been associated with leukemia risk. Cigarette smoking has a deleterious effect on survival in leukemia by shortening complete remission duration and subsequent survival. The data reported in this review are derived from the medical literature and from the experience of the authors.

Parental smoking and childhood leukemia

Childhood leukemia is the most common cancer among children, representing 31% of all cancer cases occurring in children younger than the age of 15 years in the USA. There are only few known risk factors of childhood leukemia (sex, age, race, exposure to ionizing radiation, and certain congenital diseases, such as Down syndrome and neurofibromatosis), which account for only 10% of the childhood leukemia cases. Several lines of evidence suggest that childhood leukemia may be more due to environmental rather than genetic factors, although genes may play modifying roles. Human and animal studies showed that the development of childhood leukemia is a two-step process that requires a prenatal initiating event(s) plus a postnatal promoting event(s). Despite a substantial public health effort to reduce cigarette smoking, a large proportion of the US and world population still smoke. Tobacco smoke contains at least 60 known human or animal carcinogens, with the major chemical classes being volatile hydrocarbons, aldehydes, aromatic amines, polycyclic aromatic hydrocarbons, and nitrosamines; among these chemicals, only benzene is an established leukemogen, although other chemicals in the tobacco could interact with one another in a complex way to jointly attain a significant carcinogenic effect on the development of leukemia. Although tobacco smoke is an established risk factor for adult myeloid leukemia, the studies of association between parental smoking and childhood leukemia have produced inconsistent results. The majority of the studies on maternal smoking and childhood leukemia did not find a significant positive association and some even reported an inverse association. In contrast to studies of maternal smoking, studies of paternal smoking and childhood leukemia reported more positive associations but only by less than half of the studies. Future directions to be considered for improving the study of parental smoking and childhood leukemia are: 1) consider all sources of benzene exposure in addition to smoking, including occupational exposure and traffic exhausts; 2) childhood leukemia is a heterogeneous disease and epidemiologic studies of childhood leukemia can be greatly improved by grouping childhood leukemia into more homogeneous groups by molecular techniques (e.g., structural and numerical chromosomal changes); and 3) assess gene-environment interaction. It is hoped that through the continual effort, more will be uncovered regarding the causes of childhood leukemia. In the meantime, more effort should be spent on educating the parents to quit smoking, because parental smoking is known to affect many childhood diseases (e.g., asthma, respiratory tract infection, and otitis media) that are much more prevalent than childhood leukemia.

Chronic lymphocytic leukaemia: an overview of aetiology in light of recent developments in classification and pathogenesis

This overview of the epidemiology of chronic lymphocytic leukaemia (CLL) summarizes the evolution of classification and coding systems and describes the intersection of pathogenesis and aetiology. The role of the putative precursor to CLL, monoclonal B-cell lymphocytosis (MBL), is considered, and ideas for future investigations of the MBL-CLL relationship are outlined. We discuss the epidemiology of CLL, focusing on descriptive patterns and methodological considerations. Postulated risk factors are reviewed including the role of ionizing and non-ionizing radiation, occupational and environmental chemical exposures, medical conditions and treatments, and lifestyle and genetic factors. We conclude by raising key questions that need to be addressed to advance our understanding of CLL aetiology. Recommendations for future epidemiological studies are given, including the standardization of reporting of CLL across cancer registries, the clarification of the natural history of MBL, and the circumvention of the methodological shortcomings of prior epidemiological investigations in relation to radiation, chemical exposures and infectious agents.

Tobacco and the risk of acute leukaemia in adults

Self-reported smoking histories were collected during face-to-face interviews with 807 patients with acute leukaemia and 1593 age- and sex-matched controls. Individuals who had smoked regularly at some time during their lives were more likely to develop acute leukaemia than those who had never smoked (odds ratio (OR) = 1.2, 95% confidence interval (CI) 1.0-1.4). The association was strongest for current smokers, defined here as smoking 2 years before diagnosis (OR = 1.4, 95% CI 1.1-1.7). With respect to the numbers of years smoked, risk estimates were raised in all groups except those who had smoked for fewer than 10 years. Similarly, the odds ratio decreased as the number of years 'stopped smoking' increased, falling to one amongst those who had given up smoking for more than 10 years. No significant linear trends were found, however, with either the numbers of years smoked or the numbers of years stopped smoking, and no significant differences were found between AML and ALL.

Cancer, cigarette smoking and premature death in Europe: a review including the Recommendations of European Cancer Experts Consensus Meeting, Helsinki, October 1996

Cigarette smoking has been clearly and unambiguously identified as a direct cause of cancers of the oral cavity, oesophagus, stomach, pancreas, larynx, lung, bladder, kidney and leukaemia, especially acute myeloid leukaemia. Additionally, cigarette smoking is a direct cause of ischaemic heart disease (the commonest cause of death in western countries), respiratory heart disease, aortic aneurysm, chronic obstructive lung disease, stroke, pneumonia and cirrhosis and cancer of the liver. Cigarette smoking can kill in 24 different ways and, although smoking protects against several fatal and non-fatal conditions, the adverse effect of smoking on health is largely negative. In developed countries as a whole, tobacco is responsible for 24% of all male deaths and 7% of all female deaths: these figures rise to over 40% in men in some countries of central and eastern Europe and to 17% in women in the United States. The average loss of life of smokers is 8 years. Among United Kingdom doctors followed for 40 years, overall death rates in middle age were about three times higher among doctors who smoked cigarettes as among doctors who had never smoked regularly. About half of all regular cigarette smokers will eventually be killed by their habit. The important information is that it is never too late to stop smoking: among United Kingdom doctors who stopped smoking, even in middle age, there was a substantial improvement in life expectancy. World-wide, smoking is killing three million people each year and this figure is increasing. In most countries the worst is yet to come, since by the time the young smokers of today reach middle or old age there will be about 10 million deaths/year from tobacco. Approximately 500 million individuals alive today can expect to be killed by tobacco, 250 million of these deaths will occur in middle age. Tobacco is already the biggest cause of adult death in developed countries. Over the next few decades tobacco could well become the biggest cause of adult death in the world. For men in developed countries, the full effects of smoking can already be seen. Tobacco now causes one-third of all male deaths in middle age (plus one fifth in old age). Tobacco is a cause of about half of all male cancer deaths in middle age (plus one-third in old age). Of those who start smoking in their teenage years and keep on smoking, about half will be killed by tobacco. Half of these deaths will be in middle age (35-69) and each will lose an average of 20-25 years of non-smoker life expectancy. In non-smokers in many countries, cancer mortality is decreasing slowly and total mortality rapidly. The war against cancer is being won slowly: the effects of cigarette smoking are holding back this victory. Lung cancer now kills more women in the United States each year than breast cancer. For women in developed countries, the peak of the tobacco epidemic has not yet arrived. Tobacco now causes almost one-third of all deaths in women in middle age in the United States. Although it has only 5% of the world's female population, the United States has 50% of the world's deaths from smoking in women. Tobacco smoking is a major cause of premature death. Throughout Europe, in 1990 tobacco smoking caused three quarters of a million deaths in middle age (between 35 and 69). In the Member States of the European Union in 1990 there were over one quarter of a million deaths in middle age directly caused by tobacco smoking: there were 219700 in men and 31900 in women. There were many more deaths caused by tobacco at older ages. In countries of central and eastern Europe, including the former USSR, there were 441200 deaths in middle age in men and 42100 deaths in women. There is a need for urgent action to help contain this important and unnecessary loss of life. In formulating Recommendations, the European Cancer Experts Consensus Committee recognised that Tobacco Control depends on various parts of society and not only on the individual.

Lymphohaematopoietic malignancies and quantitative estimates of exposure to benzene in Canadian petroleum distribution workers

OBJECTIVE

To evaluate the relation between mortality from lymphohaematopoietic cancer and long term, low level exposures to benzene among male petroleum distribution workers.

METHODS

This nested case control study identified all fatal cases of lymphohaematopoietic cancer among a previously studied cohort. Of the 29 cases, 14 had leukaemia, seven multiple myeloma, and eight non-Hodgkin's lymphoma. A four to one matching ratio was used to select a stratified sample of controls from the same cohort, controlling for year of birth and time at risk. Industrial hygienists estimated workplace exposures for benzene and total hydrocarbons, without knowledge of case or control status, for combinations of job, location, and era represented in all work histories. Average daily benzene concentrations ranged from 0.01 to 6.2 parts per million (ppm) for all jobs. Company medical records were used to abstract information on other potential confounders such as cigarette smoking, although the data were incomplete. Odds ratios (ORs) were calculated with conditional logistic regression techniques for several exposure variables.

RESULTS

Risks of leukaemia, non-Hodgkin's lymphoma, and multiple myeloma were not associated with increasing cumulative exposure to benzene or total hydrocarbons. For leukaemia, the logistic regression model predicted an OR of 1.002 (P < 0.77) for each ppm-y of exposure to benzene. Duration of exposure to benzene was more closely associated with risk of leukaemia than other exposure variables. It was not possible to completely control for other risk factors, although there was suggestive evidence that smoking and a family history of cancer may have played a part in the risk of leukaemia.

CONCLUSION

This study did not show a relation between lymphohaematopoietic cancer and long term, low level exposures to benzene. The power of the study to detect low-such as twofold-risks was limited. Thus, further study on exposures to benzene in this concentration range are warranted.

Elevated levels of benzene-related compounds in the urine of cigarette smokers

Benzene exposure causes leukemia and lymphomas. Recent epidemiological findings have also shown an association between cigarette smoking and an increased risk of leukemia. However, further evidence is required to document the biological plausibility of this association. In evaluating this link, it is important to note that cigarette smoke contains benzene and various pyrolytic compounds, among other carcinogens. This study aims to determine the uptake of benzene by measuring 3 benzene-related compounds in cigarette smokers and non-smokers. Urinary concentrations of catechol (CAT), hydroquinone (HQ), and trans,trans-muconic acid (tt-MA) were measured by high-performance liquid chromatography (HPLC) with fluorimetric and UV detection, respectively. The results showed that these compounds were present in all urine samples. However, the concentrations were significantly higher in smokers than in non-smokers. The mean level of urinary tt-MA was 0.19 +/- 0.09 mg/g creatinine for 46 male smokers and the corresponding value for 40 non-smokers was 0.14 +/- 0.07 mg/g creatinine. The mean concentrations of HQ and CAT were 0.81 +/- 0.4 and 3.51 +/- 2.6 mg/g creatinine for smokers, and 0.45 +/- 0.4 and 1.94 +/- 1.2 mg/g creatinine for non-smokers, respectively. These results suggest that cigarette smoking is associated with a significant additional exposure to benzene and its related compounds. Furthermore, significant correlations were observed between the concentrations of cotinine, the metabolite of nicotine, and the above compounds. These findings suggest that the exposure originated from cigarette smoking.

Myeloid leukemias and myelodysplastic syndromes: chemical exposure, histologic subtype and cytogenetics in a case-control study

We conducted a case control study of 50 acute myeloid leukemias (AML), 17 chronic myeloid leukemias (CML), 19 myelodysplastic syndromes (MDS), and 246 controls. The cases were classified according to the French-American-British (FAB) classification, and chromosome aberrations were recorded according to the International System for Human Cytogenetic Nomenclature. Exposure to suspected leukemogenic agents was assessed blindly by an industrial hygienist. Increased risks were noted for mechanics, welders, electricians, and drivers among men and among farmers and textile workers among women. Increased SMRs for leukemias in a census-based cohort study conducted in the same area (Torino) were previously reported for electricians and drivers among men and for textile workers among women. We detected nonstatistically significant increased relative risks for exposure to benzene (odds ratio, OR = 1.7), petrol refining products (1.9), polycyclic aromatic hydrocarbons (1.7), and electromagnetic fields (1.6) in men; in women, a statistically significant association with exposure to pesticides was detected [OR = 4.4; 95% confidence interval (CI) 1.7-11.5]. Although exposure to pesticides was confined to AML, MDS cases included a high proportion of subjects exposed to benzene and electromagnetic fields. No particular histologic subtype of AML was associated with chemical exposures except for that of pesticides with the M4 category. Chromosome aberrations were not associated with chemical exposures (OR = 1.0), but a nonstatistically significant excess was noted in association with electromagnetic fields (OR = 2.1).