FAMILIAL FACTORS IN HUMAN LUNG CANCER AND SMOKING

Cancer Frequency Variations Among and Within Families

Comprehension of etiologic factors in cancer requires precise recording of tumor histology, genealogy, medical history, and potential environmental carcinogens. With this approach and in a prospective and retrospective survey, two cancer-prone and two cancer-resistant families are described. Genetic factors, in cancer predisposition and in cancer resistance are hypothesized.

Cancer aggregation and complex segregation analysis of families with female non-smoking lung cancer probands in Taiwan

Previous studies have found that having a first-degree blood relative with lung cancer was a possible predictor of lung cancer risk, but some studies have indicated that the association is non-significant or only significant for a subset of the studied population. To determine the familial aggregation and whether there is any evidence for a gene controlling the susceptibility to developing lung cancer in female non-smokers, multiple logistic regression methods for estimating covariate effects and maximum likelihood segregation analyses were performed using data from 216 female non-smoking lung cancer probands (2328 individuals) in a population-based case-control study. Having a family history of lung cancer was found to be a significant predictor of lung cancer for non-smoking females (Adjusted Odds Ratio (OR)=5.7, 95% Confidence Interval (CI)=1.9-16.9). Having a female relative with lung cancer (adjusted OR=14.4, 95% CI=2.7-75.5) was more strongly associated with the lung cancer risk than was having a male relative with lung cancer. This association was stronger for probands aged less than 60 years at onset (adjusted OR=11.2, 95% CI=2.2-56.9). All of the Mendelian models fitted the data significantly better than the sporadic (no major type) model or the environmental model (P<0.00l). The Mendelian codominant models provided the best fit of the data for the early onset probands and showed a stronger effect for a major susceptibility locus for non-smoking lung cancer probands. The results of this study provide evidence that a rare autosomal codominant gene may influence the risk lung cancer in non-smoker and is responsible for the familial aggregation observed in non-smoking lung cancer patients.

Epidemiology of lung cancer

In the United States, lung cancer remains the leading cause of cancer death in both men and women even though an extensive list of risk factors has been well-characterized. Far and away the most important cause of lung cancer is exposure to tobacco smoke through active or passive smoking. The reductions in smoking prevalence in men that occurred in the late 1960s through the 1980s will continue to drive the lung cancer mortality rates downward in men during the first portion of this century. This favorable trend will not persist unless further reductions in smoking prevalence are achieved.

Biological considerations in lung cancer

Our understanding of lung cancer biology has rapidly expanded in recent years. Lung cancer, unlike most human cancers, can be traced to an environmental risk factor in the majority of cases, and this fact is reflected in the vast number of genetic alterations discovered in lung tumors whose pathogenesis is believed to be mediated by carcinogen exposure. The discovery of these alterations has led to a greater understanding of tumor development. The dramatic progress in the understanding of the genetic and molecular basis of oncogenesis and the induction of immunity has led to a rejuvenation of efforts to apply this new knowledge to this common and refractory disease. Further, the resurgent interest in cancer immunology and tumor-host interactions holds promise for the development of new approaches to treatment based on harvesting the immune systems ability to recognize these alterations. Hopefully, this understanding will lead to novel approaches with real and convincing clinical efficacy once some of these strategies are tested in carefully performed randomized clinical trials with appropriate power to detect meaningful differences.

Early detection and prevention of lung cancer

Lung cancer remains the leading cause of cancer death in the United States and is one of the world's leading causes of preventable death. Technologic advances have brought new modalities that may be useful for the early detection of lung cancer. However, because of the large number of persons at increased risk for lung cancer, screening is a formidable task. There are several risk factors that can be identified, including potential susceptibility factors, which may aid in pinpointing individuals who need to participate in regular screening programs. Aside from recognized environmental exposures including cigarette smoking, there are a number of genetic and metabolic susceptibility factors that have been examined. These include polymorphisms in the cytochrome p450 enzymes and the metabolizing capability of glutathione s-transferase or acetylation. Additionally, defects in DNA repair and in bleomycin sensitivity assays may also aid in identifying individuals who are at an increased risk for lung cancer. Additional work has been done in the area of characterizing the molecular alterations in the bronchial epithelium in high-risk smokers. This manuscript addresses only selected molecular alterations that have been examined in preneoplastic bronchial epithelium. In addition to mutations in the k-ras oncogene and the p53 gene, which are frequently seen in malignancy, alterations in the p16 gene, microsatellite instability and loss of heterozygocity are also promising potential markers of preneoplasia. The hnRNP A2/B1 gene also shows some promising increased expression in preneoplasia. Lung cancer prevention has made some strides. A number of trials with molecular and morphologic intermediate endpoints have been conducted and have suggested that some of the molecular alterations and morphologic alterations are reversible. However, the rate of spontaneous regression of these lesions is, as yet, uncharacterized. Two recent large studies, the beta-carotene and retinol efficacy trial (CARET) trial conducted in the United States and the Alpha-Tocopherol Beta Carotene (ATBC) trial conducted in Finland, both demonstrated an unexpected increased risk for lung cancer associated with beta-carotene supplementation. The EUROSCAN trial evaluation of vitamin A and N-acetylcystine also showed no benefit to supplementation in reducing risk for lung cancer. Results from the Intergroup study of 1 3-cis-retinoic acid are pending, and plans are underway for an Intergroup trial studying high selenium yeast to reduce lung cancer risk. Hopefully, the combination of identifying markers of increased risk among the numerous current and former smokers will identify high-risk populations to participate in future trials of promising agents that may lead to reduction in incidence and mortality of the leading cause of cancer death.

Lung cancer histologic type and family history of cancer

The authors studied 300 patients with pathologically confirmed cancer of the trachea, bronchus, or lung in a 16-parish (county) area of southern Louisiana. Squamous-cell carcinoma was observed most frequently among these patients (39.3%), with nearly equal numbers of adenocarcinoma (25.0%) and small cell varieties (25.5%). Patients with large cell cancer, the least frequent type (10.3%), were 4.6 years younger on average than those with small cell (P less than 0.05) or squamous cell (P less than 0.05) neoplasias. Squamous cell neoplasia was more frequent among men (45.5%) than women (22.0%) (P less than 0.05). To assess whether family history differed according to the histologic cell type of the index family member, 248 patients were interviewed with regard to a family history of neoplasia. Those with small cell cancer had the highest family-size adjusted mean number of lung cancers per family (0.28). This was 2.2 times greater than the mean number of affected persons among relatives of patients with adenocarcinoma and 1.5 times greater than the mean for the families of patients with large or squamous cell types. However, none of these differences was statistically significant. Similar results were obtained when the total number of cancers at all sites was tabulated. Probands with small cell neoplasia were again most likely to have a positive family history, but the differences between histologic types were small. Although these data suggest an association, a larger study sample is required to determine conclusively whether or not a family history of lung cancer differs according to histologic type.

Association of incident lung cancer with family history of female reproductive cancers: the Iowa Women's Health Study

A number of studies have documented the familial aggregation of lung cancer; there is at least one report that female reproductive cancers are also increased in these families. To determine if the risk exists for all reproductive cancer sites, we conducted a nested case-control study of lung cancer incidence in a cohort of 41,837 women ages 55-69 years. Women were recruited by mail and asked to provide information on education, occupation, smoking habits, physical activity, and family history of specific cancer sites among female relatives. Four year follow-up for cancer incidence was conducted using a state-wide tumor registry. Compared to random controls (n = 1900), cases (n = 152) were more likely to have reported at baseline a sister affected with cancer of the uterus [crude odds ratio (OR) = 3.4, 95% Cl = 1.7-7.0, P less than 0.01], cervix (OR = 3.2, 95% Cl 1.2-8.6, P less than 0.05), or cancer at any site (OR = 1.6, 95% Cl 1.1-2.4, P less than 0.05). A family history of an affected mother with a female reproductive cancer was also more common among the cases, but not statistically significant. Cases were less educated, more likely to work in a technical/industrial setting, less physically active, more likely to smoke, and to smoke for a longer period of time than the controls (all P less than 0.01). These differences reduced the magnitude of the family history risk indicators; only the combined category of reproductive cancer at all sites among sisters remained statistically significant. Additional family studies should be done to assess environmental factors in the relatives of the cases and controls to disentangle the influence of shared genes and shared environmental factors in these associations.

Mutagen sensitivity, smoking habits and enzyme induction in healthy middle-aged men

Unscheduled DNA synthesis (UDS) (excision-repair) of N-acetoxy-2-acetylaminofluorene (NA-AAF) damage to the DNA of human lymphocytes and levels of 3H-labeled NA-AAF bound to the DNA (carcinogen binding) of lymphocytes after 18 hr of culturing were measured in a consecutive subsample of healthy middle-aged males attending a multiphasic health screening program at the Department of Preventive Medicine in Malmö during 3 weeks in November-December 1981, and compared relative to their smoking habits, body weight, serum cholesterol, and gamma-glutamyltransferase levels as well as aryl hydrocarbon hydroxylase inducibility. This study group numbered 66 males and was uniform in sex, age, and investigation time. No case of significant arterial hypertension was present. The UDS and carcinogen binding results showed no correlation with the other factors measured, with the exception of smoking which was strongly (P less than 0.01) associated with increasing levels of both the UDS and carcinogen binding values. It is concluded that under ordinary circumstances smoking may represent the most important exogenous factor which may modulate risk to cardiovascular disease and cancer by influencing individual mutagen sensitivity.

Aryl hydrocarbon hydroxylase induction levels in patients with malignant tumors associated with smoking

The levels of aryl hydrocarbon hydroxylase (AHH) inducibility were assessed in 173 patients with cancers statistically associated with smoking, i.e., squamous cell and transitional cell carcinomas, at various sites. In 34 patients with carcinomas of the oral cavity, 41 patients with laryngeal carcinomas, and 22 patients with pulmonary carcinomas there was a highly significant overrepresentation of high inducers, whereas 30 patients with carcinomas of the renal pelvis and ureter and 46 patients with urinary bladder carcinomas did not differ significantly in this respect from a control population comprising 92 subjects with no history of neoplastic disease. The results add further support to the concept of AHH as a major activator of carcinogens belonging to the group of polycyclic aromatic hydrocarbons (PAH) when these affect the oral cavity and/or the respiratory tract. The role of AHH in urothelial carcinogenesis seems to be less explicit.

Arylhydrocarbonhydroxylase inducibility and smoking habits in patients with laryngeal carcinomas

There is considerable evidence that the inducible enzyme aryl hydrocarbon hydroxylase (AHH) plays an important role in the activation of polycyclic aromatic hydrocarbons (PAH) to ultimate carcinogens. In man, a genetic heterogeneity of AHH inducibility has been demonstrated, and correlated to susceptibility to bronchogenic carcinomas following exposure to PAH. We assessed AHH inducibility in a control group of 102 healthy Swedish citizens and in 41 patients with laryngeal carcinomas. Frequencies of the three phenotypes of high, intermediate and low AHH inducibility in our control group; 8.8%, 42.2% and 49%, respectively, did not differ significantly from frequencies found in a white US population. In the laryngeal carcinoma group, there was a statistically highly significant overrepresentation of patients with high AHH inducibility, 36.6%, whereas 43.9% had an intermediate and 19.5% a low level. Most of the patients were heavy smokers. These findings add further support to the concept that susceptibility to PAH-induced carcinomas is associated with high levels of inducible AHH activity.

Sister chromatid exchange induction by cigarette smoke

This paper presents evidence that cigarette smoke condensate (CSC) is a potent inducer of sister chromatid exchanges (SCEs) in cultured human lymphocytes; that benzo(a)pyrene (BP) contributes very little to this activity; that smokers have higher SCE rates than nonsmokers; that smokers with untreated lung cancer have consistently higher basal and CSC-induced SCE rates than their matched heavy smoking controls; and that, on a weight-for-weight basis, CSCs from different tar categories of cigarettes induce similar numbers of SCEs. These results are in keeping with the evidence that many smokers die of lung cancer, and that the basis of malignant transformation may be an alteration in cellular DNA. The results raise questions about possible innate differences in individuals' responses to cigarette smoke, and about the "safeness" of lower tar cigarettes.

Leucoplakia of the oral cavity, smoking and arylhydrocarbon-hydroxylase inducibility

In a consecutive series of 53 cases of oral leucoplakia, smoking history, oro-dental status and arylhydrocarbon-hydroxylase (AHH) inducibility were assessed. There was an increased association of leucoplakia with smoking, particularly in the male cases, but no remarkable findings as to dental status. Overall, there was a slightly higher frequency of cases with high AHH inducibility than expected from a normal control population. This difference was confined to the smokers, where there was a statistically highly significant over-representation of high AHH inducibility and under-representation of low AHH inducibility. The figures in the non-smoking patients were close to the expected.

Carcinoma of the oral cavity in relation to aryl hydrocarbon hydroxylase inducibility, smoking and dental status

The authors investigated the smoking patterns in a consecutive series of 20 patients with oral cancer and at the same time assessed the aryl hydrocarbon hydroxylase (AHH) inducibility distribution and dental status. The AHH level proved high in 8 patients, intermediate in 7 and low in 5. High AHH inducibility was more common (p = less than 0.001) and low AHH inducibility less common (p = less than 0.001) than in the controls. Dental status was poor in only 2 patients. It is concluded that smoking is a prominent exogenous factor associated with the occurrence of cancer in the oral cavity. Poor dental status seems to be of minor importance.

Variation of microsomal mixed function oxidase(s) and human lung cancer

Animal and human studies on aryl hydrocarbon hydroxylase (AHH) have demonstrated wide inter-individual variation. First attempts to link this variation to the susceptibility to certain cancers have been successful in mice but remained inconclusive in man. In a new approach, saliva antipyrine half-lives and metabolic clearance rates have been used to assess individual rates of benzo]a]pyrene metabolism in human subjects. Saliva antipyrine half-lives and metabolic clearance rates have been measured in 57 patients with lung cancer, 90% of whom had quit smoking more than three months prior to the test, 57 cancer-free matched controls, and 59 healthy smoking controls. The mean antipyrine half-life was significantly shorter (P less than 0.001) in lung cancer patients when compared with the cancer-free matched control group, but differed little from that of the smoking group (P less than 0.05). The data support the previous observation than lung cancer patients have increased oxidation rates which, in addition to smoking, might have predisposed them to developing lung cancer.

Is the role of the environment in carcinogenesis overestimated?

The dominant role of the physical and chemical environment in the development of cancer is challenged. Analyses of the etiology of skin, bladder, respiratory and gastric cancers are presented which demonstrate the considerable extent to which one's health status may modify the initiation and promotion of environmentally associated cancers. It is concluded that although environmental factors may initiate and/or promote 85 to 90 percent of all cancers this is misleading since it neglects the critical role of the individual's health status as a factor modifying carcinogenesis.

Aryl hydrocarbon hydroxylase in cultured lymphocytes of twins

Measurement of aryl hydrocarbon hydroxylase (AHH) in cultured lymphocytes of 18 monozygotic and 30 dizygotic twin pairs showed that basal and induced AHH activity and AHH inducibility are heritable traits. The data are consistent with AHH inducibility being determined by a single or a very few polymorphic genes.

The effects of smoking on the lungs

The literature relating to tobacco smoking has been reviewed and is discussed under a number of headings. The smoking habits of Australians and people of other countries, the constituents of tobacco smoke and the different types of tobacco are discussed. The effects of tobacco smoke on lung defences and and function are outlined and the evidence relating cigarette smoking to lung cancer in Australia, the UK and the USA is reviewed. The relationship between cigarette smoking and diseases which chronic air flow obstruction is outlined. Differences in smoking-related diseases in males and females and the effects of stopping smoking are included in the discussion.