Lung cancer and the debrisoquine metabolic phenotype

The Molecular Mechanism of Metabolic Remodeling in Lung Cancer

Metabolic remodeling is a key phenomenon in the occurrence and development of tumors. It not only offers materials and energy for the survival and proliferation of tumor cells, but also protects tumor cells so that they may survive, proliferate and transfer in the harsh microenvironment. This paper attempts to reveal the role of abnormal metabolism in the development of lung cancer by considering the processes of glycolysis and lipid metabolism, Identification of the molecules that are specifically used in the processes of glycolysis and lipid metabolism, and their underlying molecular mechanisms, is of great clinical and theoretical significance. We will focus on the recent progress in elucidating the molecular mechanism of metabolic remodeling in lung cancer.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Role of xenobiotic metabolic enzymes in cancer epidemiology

The cause of the majority of cancers is poorly understood albeit multifactorial. The ultimate consequence of etiological factors where defined is an alteration within the cellular genotype, which is manifested in the cells acquiring malignant phenotype. There are several environmental carcinogens that contribute to carcinogenesis. These carcinogens are metabolized by a large number of enzymes, including the cyto-chrome P 450 group, glutathione-S-transferase (GST), the uridine glucuronyl transferase (UGT) super-family, alcohol-metabolizing enzymes, sulphatases, etc. These enzymes can either inactivate carcinogens or in some cases generate reactive moieties that lead to carcinogenesis. This review summarises the available evidence regarding the role of xenobiotic metabolic enzymes and their role in cancer epidemiology. The available data and studies have identified correlates between expression of various metabolizing enzymes with risk of malignancies known to be induced by their substrates. The data may have relevance in one population but not for another for a specific malignancy and at times may be conflicting. We believe that with mature data in the future it may be possible to stratify patients by risk.

Gestational mutations and carcinogenesis

We present a mathematical formulation to evaluate the effects of gestational mutations on cancer risk. The hazard or incidence function of cancer is expressed in terms of the Probability Generating Function (PGF) of the number of normal and mutated cells at birth. Using Filtered Poisson Process Theory, we obtain the PGF for several models for the accumulation of gestational mutations. In particular, we develop expressions for the hazard function when one or two successive mutations could occur during gestation. We also calculate the hazard when the background gestational mutation rates are increased due to exposure to mutagens, such as prenatal radiation. To illustrate the use of our models, we apply them to colorectal cancer in the SEER database. We find that the proportion of cancer risk attributable to developmental mutations depends on age and that it could be quite significant when gestational mutation rates are high. The analysis of the SEER data also shows that gestational mutations could contribute to inter-individual variations in colorectal cancer risk.

Cancer incidence patterns among adolescents and young adults in the United States

OBJECTIVE

The purpose of this study was to examine age-specific cancer incidence patterns among adolescents and young adults (ages 15--49).

METHOD

Cancer incidence data for 1995--1999 from 22 population-based central cancer registries, covering about 47% of the US population, were used. Relative frequencies and average annual age-specific incidence rates per 100,000 person-year were computed for the five-year age groups from age 15--19 years through 45--49 years. Tests of significance for comparison were at a level of p<0.05.

RESULTS

The age at crossover from a predominance of non-epithelial cancers to a predominance of epithelial cancers during adolescence and young adulthood varied by gender and race. Epithelial cancer became the predominant type of tumor after age 40 years among males while it was the predominant type after age 25 years among females. There was also a shift in the top five cancer types with increasing age, which varied by race and gender. Epithelial cancers of the thyroid, breast, ovary, and cervix uteri started to increase sharply among young women in their 20s while among males epithelial cancers rarely occurred until the early 30s (ages 30--34). Cancers of the female breast, colon and rectum, and lung began to occur at an earlier age and increased more sharply among blacks than among whites. However, the incidence rates of epithelial thyroid and ovarian cancers rose more quickly among whites than blacks. Non-Hodgkin lymphoma and soft tissue sarcoma (excluded Kaposi's sarcoma) increased with age among both whites and blacks but the rates were significantly higher among blacks than among whites. Both Kaposi's sarcoma and testicular cancer incidence increased with age and peaked in the early 30s (ages 30--34). The former was significantly higher among blacks than whites while the latter was significantly higher among whites than blacks. Cervical cancer incidence leveled off when white women reached their 30s, but for black women the rate continued to rise with advancing age. Cutaneous melanoma rates were significantly higher among females than among males between the ages of 15 and 39. Conclusion Cancer incidence patterns among adolescents and young adults are distinctive. Specific cancer prevention and control strategies should be targeted accordingly and tailored to their specific needs.

Modulation of the primary and the secondary antibody response by tobacco smoke condensates

Cigarette smoke condensate administered to C57BL/6 mice led to a decrease in the primary antibody response to OVA (hen egg albumin) antigen. Selenium (Se)-supplementation allowed to relieve significantly this inhibition. Moreover, even being not supplemented with Se, a preparation was found devoid of inhibitory effects. Furthermore, the presence of Se-supplemented tobacco smoke condensate at the time of antigen priming, contributed to an enhanced secondary antibody response.

In vitro and in vivo immunotoxic and immunomodulatory effects of nonsupplemented and selenium-supplemented cigarette smoke condensate

Cigarette smoke condensate has been evaluated for its in vitro and in vivo immunotoxic and immunomodulatory properties. It was found that cigarette smoke condensate used in vitro at concentration from 6.6 to 20 microg/ml exerted pronounced inhibitory effects upon cell surface antigen-presenting major histocompatibility complex class I (MHC-I) expression and immunoglobulin (Ig) synthesis. In vivo, i.p. administration of cigarette smoke condensate to C57BL/6 mice before challenging with ovalbumin (OVA) antigen, has led to a decrease of anti-OVA specific antibody response. This inhibition affected more Ig protein synthesis than membrane bound MHC-I expression. Supplementation with selenium (Se) significantly reduced the inhibitory effects both in vitro and in vivo.

Women and small cell lung cancer: social characteristics, medical history, management and survival

The literature make it clear that lung cancer in women differs from that in men in several specific aspects. We conducted a retrospective study of the 967 consecutive recorded patients (696 men and 91 women after exclusions) diagnosed with small cell lung cancers (SCLC) between 1981 and 1994 in the Bas-Rhin population-based cancer registry to determine if such particularities could be observed in SCLC. Data included demographic and social characteristics, medical and smoking history, management (diagnosis and treatment), hospitalisation and survival. The end point for survival was 31 December 1998. Women were more frequently single, divorced, or widowed (P=0.007) and lived more often in urban areas (places with more than 10,000 inhabitants) (P=0.017). They differed significantly from men in their tobacco exposure (P=0.0001) and non-smoking rates (P=0.0003) but not in clinical presentation, except for more frequently elevated LDH levels (P=0.02). Bone marrow biopsies were more often performed in men (P=0.004), but management was otherwise comparable. The mean number of hospitalisations (for any reason) was comparable in both sexes but women tended to remain hospitalised longer (P=0.057). Overall survival did not differ, but women older than 70 years died sooner than their male counterparts (P=0.026). Our study confirms that some of gender differences reported in the lung cancer literature exist in SCLC. Sex-related differences in LDH levels have not previously been reported, to our knowledge. North American and European data concerning survival among women and men are discordant. Whether these gender differences are related to a real difference between the sexes or simply to differential exposure to carcinogens remains to be determined.

Candidate gene case-control studies

Two main approaches to the identification of genes are involved in polygenic diseases. Use of family studies has generally been the preferred approach up until recently, but this is only feasible if the genetic component of the disease is relatively strong and DNA samples are available from other family members. Population case-control studies are useful both as an alternative and an adjunct to family studies. These can involve either whole genome scanning or candidate gene approaches. While whole genome scanning is likely to be widely used in the future once more information on genome-wide single nucleotide polymorphism distributions is available, at present, candidate gene studies are more feasible. When performing candidate gene case-control studies factors such as study design, methods for recruitment of case and controls, selection of candidate genes, functional significance of polymorphisms chosen for study and statistical analysis require close attention to ensure that only genuine associations are detected. Some examples of the successful use of candidate gene case-control studies are discussed and, to illustrate some potential problems in the design and interpretation of association studies, some specific examples of association studies on cancer are considered.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Candidate gene case-control association studies: advantages and potential pitfalls

There is increasing information on the importance of genetic polymorphisms in human genes. Polymorphisms occur on average once every 500-1000 base pairs in the human genome and are useful in the identification of genes involved in human disease. Some genetic polymorphisms have functionally significant effects on the gene product and are the most useful type of polymorphism in disease association studies while others are simply useful markers. There are two main approaches using polymorphisms in the identification of genes involved in polygenic diseases. The first involves examining inheritance patterns for genetic polymorphisms in family studies and the second case-control studies which compare genotype frequencies for candidate disease genes in unrelated individuals with the disease and healthy controls. Use of family studies is generally the preferred approach but this is only feasible if the genetic component of the disease is relatively strong, DNA samples are available from other family members and the disease is relatively easy to diagnose and is not stigmatized. Population case-control studies are useful both as an alternative and an adjunct to family studies. When performing case-control studies factors such as study design, methods for recruitment of cases and controls, functional significance of polymorphisms chosen for study and statistical analysis of data require close attention to ensure that only genuine associations are detected. To illustrate some potential problems in the design and interpretation of association studies, some specific examples of association studies on drug response and on disease susceptibility involving receptor genes, cytochrome P450 and other xenobiotic metabolizing enzyme genes and immune system genes including TNF-alpha, IL-10 and the IL-4 receptor are discussed.

The epidemiology of lung cancer

Lung cancer continues to be the leader in cancer deaths in the United States. The incidence of lung cancer in men has slowly decreased since the late 1980s, but has just now begun to plateau in women at the end of this decade. Despite modest advances in chemotherapy for treating lung cancer, it remains a deadly disease with overall 5-yr survival rates having not increased significantly over the last 25 years, remaining at approximately 14%. Tobacco smoking causes approximately 85-90% of bronchogenic carcinoma. Environmental tobacco exposure or a second-hand smoke also may cause lung cancer in life-long non-smokers. Certain occupational agents such as arsenic, asbestos, chromium, nickel and vinyl chloride increase the relative risk for lung cancer. Smoking has an additive or multiplicative effect with some of these agents. Familial predisposition for lung cancer is an area with advancing research. Developments in molecular biology have led to growing interest in investigation of biological markers, which may increase predisposition to smoking-related carcinogenesis. Hopefully, in the future we will be able to screen for lung cancer by using specific biomarkers. Finally, dietary factors have also been proposed as potential risk modulators, with vitamins A, C and E proposed as having a protective effect. Despite the slow decline of smoking in the United States, lung cancer will likely continue its devastation for years to come.

Cancer risk and low-penetrance susceptibility genes in gene-environment interactions

PURPOSE

To provide a concise review for human cancer risk related to low-penetrance genes and their effects on environmental carcinogen exposure.

METHODS

Citation of relevant and recent references for molecular epidemiology, focusing on lung cancer, ethical issues, and some clinical implications of recent molecular epidemiology studies.

RESULTS

Low-penetrance genes contribute to cancer risk by augmenting the effects of carcinogen exposures. These exposures can be measured in the body through molecular dosimetry (ie, the amount of DNA damage), which reflects a biologically effective dose. The examination of tumors and the mutations within tumor suppressor genes, such as p53, can provide etiologic clues for both exposure and susceptibility. Although many studies have focused on carcinogen metabolism and cancer risk, more recent studies are considering DNA repair. Also, we are learning that behavior, such as tobacco addiction, also may be genetically controlled.

CONCLUSION

Sporadic cancers are caused by gene(n)-environment(n) interactions rather than a dominant effect by a specific gene, environmental exposure, or gene-environment interaction. New paradigms, where we categorize genes as caretaker or gatekeeper genes, will allow for new hypotheses to be tested and will require advanced methods of analysis. The goal of molecular epidemiology is to develop risk assessment models for individuals, but currently the most achievable goal will be population risk assessment and a better understanding of carcinogenesis.

Female lung cancer mortality and sex ratios at birth near a petroleum refinery plant

This study was conducted to assess whether female mortality from lung cancer is associated with residence in communities adjacent to a petroleum refinery plant and whether petroleum air pollution could affect the sex ratios of births. The Kaohsiung Refinery of the Chinese Petroleum Corp. is the oldest oil refinery in Taiwan and is located between the Tso-Ying and the Nan-Tzu municipalities. Standardized mortality ratios (SMRs) for female lung cancer and sex ratios of births were calculated for each municipality for the years 1971-1996. Cumulative-sum techniques were used to detect the occurrence of changes in the SMRs. The study results show that mortality from female lung cancer rose gradually about 30 to 37 years after the operation of a petroleum refinery plant began. However, the association between exposure to the petroleum air pollution and abnormal sex ratios at birth was not significant.

Predisposition to lung tumorigenesis

Mouse inbred strains with inherited predisposition and resistance to lung cancer provide an essential tool for the dissection of the genetics of this complex disease. We have previously mapped a major locus (Pulmonary adenoma susceptibility 1, Pas1) affecting inherited predisposition to lung cancer in mice on chromosome 6, near Kras2. Appropriate crosses that include susceptible mice (Pas1(s)) provide a model system for identifying loci that can modify the lung cancer predisposition phenotype caused by Pas1. Using this approach we have mapped the Pulmonary adenoma resistance 1 (Par1) locus that behaves like a modifier locus of Pas1. More recently, we mapped additional lung tumor resistance loci (Par2, and Par4), and a locus specifically involved with lung tumor progression (Papg1). The mapping of Pas1 in mice stimulated us to test the possible association of genetic markers located in the homologous human region (12p12) with risk and prognosis of lung adenocarcinomas in man. In the Italian population, we carried out an association study by genotyping lung adenocarcinoma patients and healthy controls for genetic markers located in the putative region of interest. Homozygosity of the A2 allele at a Kras2/RsaI polymorphism, and allele 2 at a VNTR polymorphism in the PTHLH gene showed borderline statistically significant associations with lung cancer risk. Furthermore, the same alleles were significantly associated with tumor prognosis. Studies on association were then performed in the Japanese and in European populations. In the Japanese population, the KRAS2/RsaI marker was significantly associated with prognosis of lung adenocarcinoma, whereas the European study did not confirm this association. Our results may provide evidence for the existence of the human PAS1 locus, suggesting that the mouse model of inherited predisposition to lung tumorigenesis is predictive of a human genetic mechanism of susceptibility to lung cancer.

Recent advances in understanding the molecular basis of polymorphisms in genes encoding cytochrome P450 enzymes

The cytochrome P450 superfamily is known to exhibit a high degree of genetic polymorphism and polymorphisms associated with absent or low enzyme activity in CYP2D6, CYP2C19 and CYP2C9 are particularly well studied. However, despite early reports of strong disease associations for particular CYP2D6 phenotypes, these have not been confirmed in recent, more detailed studies and it now appears that analysis of CYP2D6, CYP2C19 and CYP2C9 genotype is of most value in predicting metabolism of specific drugs. Polymorphisms in other cytochrome P450 genes are less well studied and appear not to be associated with complete absence of enzyme activity. We have recently carried out studies of polymorphism in both CYP1A1 and CYP2E1. The molecular basis of the apparent CYP1A1 'high inducibility' polymorphism was investigated by studying CYP1A1 and Ah receptor polymorphisms in a group of phenotyped individuals who were genotyped both for known and novel CYP1A1 and Ah receptor polymorphisms. Three novel polymorphisms in CYP1A1 (C(-459)T, G(-469)A and C(4151)T) and one in the Ah receptor (G(1768)A; V(570)I) were detected by single strand conformational polymorphism analysis and DNA sequencing. Among both novel and previously known polymorphisms, only the Ah receptor G(1721)A polymorphism, which has an allele frequency of 0.12 in Caucasians and was detected previously in a Japanese population, was significantly associated with high induced CYP1A1 activity. In the case of CYP2E1, we have detected three polymorphisms in the promoter region (A(-316)G, T(-297)A and G(-35)T) and one in the coding sequence (G(4804)A; V(179)I) by screening Caucasian DNA samples. The significance of these alleles has been investigated but only G(-35)T combined with T(-297)A, which has an allele frequency of 0.05, appears to be of functional significance, with an apparent 1.8-fold increase in levels of transcriptional activity compared with the wild-type.

Activation of procarcinogens by human cytochrome P450 enzymes

Enzymatic transformation of most chemical carcinogens is requisite to the formation of electrophiles that cause genotoxicity, and the cytochrome P450 (P450) enzymes are the most prominent enzymes involved in such activation reactions. During the past 15 years the human P450 enzymes have been extensively characterized. Considerable evidence exists that the variation in activity of these enzymes can have important consequences in the actions of drugs. Other studies have been concerned with the activation of procarcinogens by human P450s. Assignments of roles of particular P450s in the metabolism of chemical carcinogens are discussed, along with the current state of evidence for relationships of particular P450s with human cancer.

The molecular epidemiology of lung cancer

One in ten tobacco smokers develops bronchogenic carcinoma over a lifetime. The study of susceptibility of an individual and a population to lung cancer traditionally has been limited to the study of tobacco smoke dose and family history of cancer. New insights into lung carcinogenesis have made the study of molecular markers of risk possible in human populations in the emerging field of molecular epidemiology. This review summarizes data addressing the relationships of human lung cancer to polymorphisms of phase I procarcinogen-activating and phase II-deactivating enzymes and intermediate biomarkers of DNA mutation, such as DNA adducts, oncogene and tumor suppressor gene mutation, and polymorphisms. These parameters are reviewed as they relate to tobacco smoke exposure, procarcinogen metabolizing polymorphisms, and the presence of lung cancer. Problem areas in biomarker validation, such as cross-sectional data interpretation; tissue source, race, statistical power, and ethical implications are addressed.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

Pharmacogenetics: a laboratory tool for optimizing therapeutic efficiency

Pharmacogenetics is the study of the linkage between an individual’s genotype and that individual’s ability to metabolize a foreign compound. Differences in metabolism of therapeutics can lead to severe toxicity or therapeutic failure by altering the relation between dose and blood concentration of the pharmacologically active drug. Phenotypes exhibiting poor and ultraextensive metabolism result from genetic variance (polymorphism) of enzymes involved in metabolism. Thus, in pharmacogenetic studies one applies genotyping of polymorphic alleles encoding drug-metabolizing enzymes to the identification of an individual’s drug metabolism phenotype. This knowledge, when applied to dosing or drug selection, can avoid adverse reactions or therapeutic failure and thus enhance therapeutic efficiency. More than 25 commonly prescribed medicines are metabolized by the cytochrome P-4502D6 (CYP2D6) isoenzyme, and polymorphism of the CYP2D6 gene affects the therapeutic management of up to 17% of individuals in some ethnic groups. In this review, we summarize and update information concerning drug-metabolizing genotypes with emphasis on CYP2D6 genotyping techniques that can be applied by the clinical laboratory for linking human genetics to therapeutic management.

The sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer: a meta-analysis

OBJECTIVE

To examine the association between the sparteine/debrisoquine (CYP2D6) oxidation polymorphism and the risk of lung cancer.

METHOD

Meta-analysis of case-control studies using a random effects model. The "Main outcome measure" was the odds ratio for the risk of lung cancer, using extensive metabolisers as the reference group.

RESULTS

Thirteen studies were identified. The studies were too heterogeneous to be pooled the size of the odds ratio increased with the sample size. When the analysis was restricted to the largest studies, there was no difference in risk between poor and extensive metabolisers (odds ratio 0.95, 95% confidence interval 0.68-1.33).

CONCLUSION

No association was found between the CYP2D6 oxidation polymorphism and lung cancer risk when sample size bias was taken into account.

Analysis of L-myc and GSTM1 genotypes in Chinese non-small cell lung carcinoma patients

The genotypes of L-myc and GSTM1 genes were studied in normal lung tissues of 98 non-small cell lung carcinoma (NSCLC) patients from Hong Kong using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) techniques. Results showed a statistical difference in L-myc genotypes between Chinese and African Americans (P = 0.02). A significant deficit in heterozygotes resulting in the departure from Hardy-Weinberg equilibrium in lung cancer female patients was detected (0.01 < P < 0.02). There were significant differences in survival times in patients having L-L and S-S genotypes, with shorter survival times in the patients with L-L genotypes (0.01 < P < 0.05). Data on age, size of tumor, histological types, and lymph node metastasis showed no significant association with L-myc genotype. The survival time in the GSTM1-negative (null gene) group was significantly different from the GSTM1 positive group between 16 and 24 months after operation (0.01 < P < 0.05). There was no significant difference in the distribution of GSTM1 genotypes between Chinese and Caucasian Americans.

Aspects of the epidemiology of lung cancer in smokers and nonsmokers in the United States

While it is well-established that smoking is the predominant risk factor for lung cancer, it is clear that factors other than smoking and occupational exposure play a role in some lung cancers, and particularly adenocarcinoma. Data from a large, hospital-based case-control study are used to examine the association of smoking-related risk factors (amount smoked, filter status, mentholation, and differences in smoking habits between blacks and whites) and selected factors other than smoking (environmental tobacco smoke, previous primary cancer and radiotherapy, reproductive and endocrine factors, and body mass index) with lung cancer. Although smoking shows a dose-response relationship with all major lung cancer cell types, the strength of the relationship is weaker for adenocarcinoma, suggesting that other risk factors must play an important role for this cell type. In blacks and whites of both sexes, odds ratios for lung cancer increased with increasing cumulative tobacco tar intake and decreased with years since quitting smoking. Use of mentholated cigarettes was associated with no greater risk for lung cancer than that associated with the use of nonmentholated cigarettes. Exposure to environmental tobacco smoke generally showed little relation to lung cancer risk. In particular, exposure of nonsmoking wives to a husband's smoking showed no increase in risk. A history of a reproductive primary cancer and a history of radiotherapy were each associated with a fourfold increase in risk in female nonsmokers. An association of lean body mass with lung cancer was observed in current smokers, ex-smokers, and female never smokers. These results are discussed in the context of existing studies. In conclusion, variation in lung cancer rates between populations may be due to: (1) differences in effective exposure to tobacco smoke carcinogens; (2) differences in factors which modify the effect of tobacco smoke, including differences in host susceptibility and metabolism of carcinogens, or (3) differences in exposure to other independent risk factors for lung cancer.

United States lung carcinoma incidence trends: declining for most histologic types among males, increasing among females

BACKGROUND

Lung carcinoma is now the most frequently diagnosed major cancer in the world and is also the most common cause of cancer deaths in males and females in the United States and worldwide. Based on trends in cigarette smoking and on analysis of lung cancer rates by birth cohort, it was predicted that a decline would occur in age-adjusted lung cancer rates, initially in males, and approximately 10 years later in females. We evaluated age-adjusted lung cancer incidence rates for changes in trends by race, sex and histologic type to determine if and when rates may have started declining.

METHODS

We analyzed population-based incidence data from the National Cancer Institute's Third National Cancer Survey conducted between 1969 and 1971 and from the Surveillance, Epidemiology and End-results (SEER) program conducted between 1974 and 1991. Age-adjusted rates were plotted by time period using a logarithmic scale for the ordinate. We used regression methods for grouped time-to-response data to fit a model to the disease rate for age, and calendar year to estimate the calendar year of maximum disease rate.

RESULTS

During this period, the overall age-adjusted lung cancer incidence rate rose from 37.8 to 68.2 per 100,000. Lung cancer rates in both white and black males climaxed around 1984 and declined subsequently. Furthermore, among white and black males, the rates of squamous cell carcinoma, small cell carcinoma, and large cell carcinoma declined after peaks in 1981 and 1982, 1986 and 1987, and 1986 and 1988, respectively. The rates for adenocarcinoma in black males peaked in 1987 whereas the rates in white males appeared to have plateaued between 1989 and 1991. Total lung cancer rates in males exceeded those in females, with rates in black males exceeding rates in white males. Age-adjusted lung carcinoma rates among white and black females continued to increase for all histologic types with the exception of large cell carcinoma among whites, bronchioloalveolar carcinoma among whites and blacks, and adenosquamous carcinoma among blacks.

CONCLUSIONS

The cumulative effect of these trends has resulted in a plateau of total lung carcinoma incidence in all persons combined, and a decline might be expected soon, as has already been observed among males. Most of these changes reflect past cigarette smoking patterns. Demonstration of declines and tapering increases among several population subgroups suggests impending reductions in the incidence and mortality rate for this highly fatal cancer.

The role of cytochrome P450 enzymes in hepatic and extrahepatic human drug toxicity

The human cytochrome P450 enzyme system metabolises a wide array of xenobiotics to pharmacologically inactive metabolites, and occasionally, to toxicologically active metabolites. Impairment of cytochrome P450 activity, which may be either genetic or environmental, may lead to toxicity caused by the parent compound itself. In practise, this usually only applies to drugs that have a narrow therapeutic index and when their clearance is critically dependent upon the fraction normally metabolised by that pathway. P450 enzymes may also convert the drug to a chemically reactive metabolite, which, if not detoxified, may lead to various forms of hepatic and extrahepatic toxicity, including cellular necrosis, hypersensitivity, teratogenicity, and carcinogenicity, depending on the site of formation and the relative stability of the metabolite, and the cellular macromolecule with which it reacts. Variation in the regulation and expression of the drug metabolising enzymes may play a key role in both interindividual variation in sensitivity to drug toxicity and tissue-specific damage. Avoidance of toxicity may be possible in rare instances by prediction of individual susceptibility or by designing new chemical entities that are metabolised by a range of enzymes (both cytochromes P450 and others) and do not undergo bioactivation.

Lung cancer

BACKGROUND

Lung cancer is the most common cause of cancer death in the United States, and its incidence has been rising for at least 50 years. Shifts in histologic type and differences in sex and race distribution have accompanied the increased incidence of lung malignancies.

METHODS

Population-based data regarding lung cancer reported to the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program for the 15-year period 1973-1987 were analyzed.

RESULTS

Results indicate that from 1973-1977 to 1983-1987, the age-adjusted rates of lung cancer increased by 30%, with the gain markedly greater in women (70%) than in men (17%). The largest percentage increases in age-adjusted rates were observed for small cell carcinoma and adenocarcinoma (approximately 60% each), with a more modest change for squamous cell carcinoma (+ 14%). For squamous cell carcinoma, the age-adjusted rates increased substantially for black (65%) and white (70%) women and only slightly for black men (10%), whereas it decreased slightly in recent years for white men.

CONCLUSIONS

In recent years, adenocarcinoma has replaced squamous cell carcinoma as the most frequent histologic subtype for all sexes and races combined. These shifts in histologic types by sex and race may be related to differences in exposure to tobacco products, dietary factors, environmental or occupational carcinogens, and host characteristics. Increased use of transbronchial and needle biopsy may have also influenced these trends to some extent. Over the study period, 5-year relative survival rate did not change appreciably for lung cancer, suggesting that therapeutic advances have had little effect.

Risk factors for lung cancer in Rio de Janeiro, Brazil: a case-control study

The association between the risk of lung cancer and tobacco smoking, dietary factors and occupational exposures was examined in a hospital-based case-control study. The study involved 123 consecutive cases and 123 controls, matched by age (+/- 3), sex, and race. In this first study of lung cancer risk in Brazil, we found that tobacco smoking is the strongest risk factor with an odds ratio (OR) for current and former smokers of 22 (CI, 6.5-76) and 7.7 (CI, 2.2-27), respectively. An OR of 2.8 (CI, 1.0-7.7) was found for users of black tobacco in the form of hand-rolled cigarettes) in combination with conventional cigarettes, after adjustment for life-time consumption of any kind of tobacco; users of conventional cigarettes only were considered as a reference group. Cessation of smoking had an important influence in reducing the lung cancer risk, whereas early initiation of smoking increased the risk. Among dietary factors, frequent consumption of meat (P < 0.01) and pasta (P = 0.02) were positively associated with lung cancer risk after adjusting for smoking and income. No association was found with green/yellow vegetables or fruits. We were unable to detect any significant association related to occupational exposures. This study confirmed the association of lung cancer with smoking as the most important predictor of risk. It also indicates the increase in risk associated with the use of black tobacco in combination with conventional cigarettes.

Reaching toward and beyond the year 2000 goals for cigarette smoking. Research and public health priorities

The 1980s witnessed decreases in adult smoking prevalence in the face of increasing morbidity and mortality from past and current tobacco use. To facilitate even greater cessation activity, innovative research continues to be conducted on methods of improving intensive, individual approaches to smoking cessation, particularly through pharmacologic intervention. However, the major thrust in this country today is toward broad, systemic, public health campaigns, targeting selected high risk groups and the general public. Vulnerable populations continue to include various ethnic groups, especially those with unusually low or high prevalence, women, persons with smoking-related diseases, and heavy smokers. Self-help methods, physician advice, work site and community based interventions, and antismoking coalitions have been in the forefront. Methodologic and intervention studies are needed, concurrent with ongoing large scale public health efforts. What efforts in research and in the public arena are requisite to reach the year 2000 goals for tobacco use? Prevention remains the number one priority. Bringing about a substantial decline in teenage smoking will require the combination of school based programs, environmental and advertising restrictions, and societal revision of norms toward the relative dangers of smoking and drug use in adolescence. Research is needed to define the optimal combinations of such interventions with booster components to sustain effects. Public health efforts, symbolized by the Community Intervention Trial for Smoking Cessation (COMMIT) and the American Stop Smoking Intervention Study (ASSIST) programs, must be combined with stronger advocacy, taxation, antismoking policy formation and implementation to realize a smoke free society.