Brain tumor risk in children in relation to use of electric blankets and water bed heaters. Results from the United States West Coast Childhood Brain Tumor Study

The possible relation between the occurrence of brain tumors in children and exposure to electric blankets or electrically heated water beds was investigated in a multicenter, population-based case-control study conducted on the West Coast of the United States. Information on maternal exposure during pregnancy or direct exposure to the subject child was collected by in-person interview from the mothers of 540 case children and 801 control children. Cases were 19 years of age or younger and were diagnosed between 1984 and 1991. Controls were recruited using a random digit dialing procedure. The risk of brain tumor occurrence from in utero exposure to either electric blankets (odds ratio (OR) = 0.9, 95% confidence interval (Cl) 0.6-1.2) or heated water beds (OR = 0.9, 95% Cl 0.6-1.3) was not elevated. Brain cancer risk did not vary by use in any trimester of pregnancy, and children with mothers who reported use throughout their pregnancy had no increased risk. Similar results were observed for exposure to the child, in that no association between brain cancer and use of electric blankets (OR = 1.0, 95% Cl 0.6-1.7) or heated water beds (OR = 1.2, 95% Cl 0.7-2.0) was observed. Risks did not vary significantly by age, sex, race, socioeconomic status, or histologic category for either in utero exposure or child's exposure. This study provides no evidence to support the hypothesis that there is a relation between brain cancer occurrence in children and 50-/60-Hz magnetic field exposure from the use of electric blankets and heated water beds.

Childhood brain tumors and exposure to tobacco smoke

Brain tumors are the second most common cancer in children after leukemia, yet the etiology of childhood brain tumors remains unknown. Tobacco smoke contains several dozen compounds that are known to be carcinogens. Among these are N-nitroso compound precursors, principally tobacco-specific nitrosamines. Although smoking has not been identified as a significant risk factor for the development of brain tumors in adults, fetuses and infants have incompletely formed blood-brain barriers that may allow the passage of carcinogenic tobacco metabolites into the central nervous system and initiate the formation of neural tumors. In this review, we present data from case-control and cohort studies published between 1971 and 1995 that examined the relationship between parental smoking during pregnancy and childhood brain tumors (CBTs). The majority of these studies found little association between CBTs and maternal smoking before or during pregnancy or between CBTs and maternal exposure to passive smoke during pregnancy.

Prenatal exposure to tobacco smoke and childhood brain tumors: results from the United States West Coast childhood brain tumor study

Data from a large, population-based case-control study were analyzed to investigate the relationship between prenatal exposure to tobacco smoke and childhood brain tumors (CBTs). A total of 540 CBT patients, diagnosed between 1984 and 1991, were identified from population-based tumor registries in 19 West Coast counties that included Seattle, WA (13 counties), San Francisco, CA (5 counties), and Los Angeles, CA (1 county). Random digit dial was used to select 801 control subjects from the three geographical regions to obtain a case:control ratio of 1:2 in San Francisco and Seattle and 1:1 in Los Angeles. The data first were analyzed separately by geographical site and then were combined with adjustments made for gender, age at the time of diagnosis (or reference date of control subjects), birth year of the index child, and maternal race. No association was found between the risk of CBTs and maternal or paternal smoking before pregnancy and there was no association between CBTs and maternal smoking during pregnancy [odds ratio (OR) = 0.98; 95% confidence interval (CI) = 0.72-1.3]. A slightly increased OR for CBTs was found for paternal smoking during pregnancy in the absence of maternal smoking (OR = 1.2; 95% CI = 0.90-1.5) and for maternal exposure to passive smoke from any source (OR = 1.2; 95% CI = 0.95-1.6). The results of this analysis are consistent with results from several prior epidemiological studies that showed no significant association between CBTs and maternal smoking before or during pregnancy or maternal exposure to passive smoke during pregnancy.

Cervical intraepithelial neoplasia, cervical cancer, and HPV

Major progress has been made to control cervical cancer in the United States and Europe using screening programs, although it remains a major cause of morbidity and mortality in the developing world. The association between cervical cancer and a sexually transmissible etiologic agent was hypothesized long before identification of human papillomaviruses (HPV) as agents that infected the genital tract. HPVs are among the most common sexually transmitted agents and have been shown to induce several squamous anogenital cancers, including squamous cell cancer of the cervix. After an etiologic role for HPV was identified in cervical cancer and CIN, efforts to understand the molecular biology of HPV were greatly expanded, enhanced by the advent of deoxyribonucleic acid (DNA) probes to identify HPV infection. Recent research has focused on specific types of HPV in relation to other recognized risk factors in the pathogenesis of CIN and invasive cervical cancer.

Intraocular melanoma linked to occupations and chemical exposures

We conducted a case-control study in the western United States to determine the relation between occupations or chemical exposures and increased risk of uveal melanoma. Among men (221 patients, 447 controls), we found increased risks for occupational groups who had intense exposure to ultraviolet light [odds ratio (OR) = 3.0; 95% confidence interval (CI) = 1.2-7.8], welding exposure (OR = 2.2; 95% CI = 1.3-3.5), and asbestos exposure (OR = 2.4; 95% CI = 1.5-3.9 for most likely exposed). The highest odds ratio was for the small number of men (nine cases, three controls) who were chemists, chemical engineers, and chemical technicians (OR = 5.9; 95% CI = 1.6-22.7). Odds ratios also were elevated for exposures to antifreeze, formaldehyde, pesticides, and carbon tetrachloride, but these findings, based on recall of specific chemical exposures, are more subject to recall bias than the findings based on occupational groups.

Cutaneous melanoma in women: anatomic distribution in relation to sun exposure and phenotype

An analysis of the relationship between the anatomic site of cutaneous melanoma, sun exposure, and phenotype was conducted in 355 women with histologically confirmed superficial-spreading melanoma and in 935 control subjects. The most frequent site for superficial-spreading melanoma was the leg. However, when major sun-related and phenotype risk factors were examined by site, risk ratios were lowest for melanomas that occurred on the leg. A history of frequent sunburns during elementary or high school, increased number of self-assessed large nevi, and blond hair were more strongly associated with melanoma sites other than the leg. Tumors on the trunk were more likely than tumors at other sites to be associated with histological evidence of a preexisting nevus. Results of this work indicate that associations between melanoma phenotypic factors may differ by anatomic site.

Cutaneous melanoma in women. V. Characteristics of those who tan and those who burn when exposed to summer sun

We studied 338 Caucasian women with superficial spreading melanoma (hereafter called melanoma) and 872 control subjects ages 25-59 years and compared characteristics of women who reported that they tanned with sun exposure with those who reported that they burned. The purpose of the study was to investigate how skin type, as measured by tendency to burn or tan, modified the effect of other melanoma risk factors. There was a clear relation between tendency to burn and prevalence of red hair, light complexion, freckles, and history of sunburns during elementary school and high school. Host factors such as light complexion and increased number of self-assessed large nevi elevated risk of melanoma among women of all skin types. Increased risk for melanoma associated with frequent sunburns during childhood and adolescence was most pronounced for women who burned and then tanned; risk was not substantially elevated for women who burned without tanning. Women who had a history of sunburns had an increased melanoma risk even if they reported tanning.

Risk of cutaneous melanoma associated with a family history of the disease. The International Melanoma Analysis Group (IMAGE)

In a combined analysis of 2952 melanoma patients and 3618 controls from 8 case-control studies in white populations the risk of cutaneous melanoma was 2.24-fold higher (95% CI, 1.76-2.86) in subjects who reported at least one affected first-degree relative than in subjects who did not. There was no evidence for heterogeneity in the relative risk between the studies, which were from a wide range of latitudes and hence degrees of sun exposure. The effect of family history on melanoma risk was independent of age, naevus count, hair and eye colour, and freckling. There was no evidence for a relationship between family history and primary site of melanoma but there was some suggestion that the familial patients were more likely to have superficial spreading melanoma or lentigo maligna melanoma than acral lentiginous melanoma or nodular melanoma.

Risk of cutaneous melanoma associated with pigmentation characteristics and freckling: systematic overview of 10 case-control studies. The International Melanoma Analysis Group (IMAGE)

Using individual subject data from 10 case-control studies, comprising over 3000 cases and almost 4000 controls, we have estimated the relative risk of melanoma associated with aspects of complexion, namely, hair, eye and skin colour and freckling in adulthood, and have examined the relationships between these factors and naevus count in terms of melanoma risk. Compared with individuals with black or dark brown hair, the relative risks for developing melanoma in those with light brown, blonde and red hair were 1.49 (95% CI 1.31, 1.70), 1.84 (95% CI 1.54, 2.21) and 2.38 (95% CI 1.90, 2.97), respectively. Individuals with blue eyes had a risk 1.55 (95% CI 1.35, 1.78) times that for those with brown eyes, or 1.15 (95% CI 0.94, 1.40) after adjusting for hair colour and freckling in adulthood. The relative risks associated with hair and eye colour were independent of those for naevus count and skin colour. Light skin colour and high freckle density were also highly significant risk factors, independent of each other and of naevus count and hair and eye colour. The risks associated with these factors, while individually modest, are largely independent, and thus pigmentation characteristics and freckling tendency should be useful in identifying high risk groups to be targeted for prevention.

Cutaneous melanoma in women. II. Phenotypic characteristics and other host-related factors

A total of 452 women with cutaneous malignant melanoma and 930 control subjects aged 25-59 years participated in a population-based case-control study carried out in the San Francisco Bay Area between 1981 and 1986. Interviews were conducted in the homes of the women. Questions were asked about various phenotypic characteristics, including eye, hair, and complexion color, presence of freckles, and number of nevi, as well as medical history, history of exposure to sunlight, ability to tan, occupation, use of cigarettes and alcohol, and demographic factors. Histologic type of melanoma was considered in the analysis: 355 (79%) women were diagnosed with superficial spreading melanoma, 61 (13%) had nodular melanoma, 13 (3%) had lentigo maligna melanoma, and 23 (5%) had other melanomas that could not be further classified. For all cutaneous melanoma subjects combined, univariate results related to host factors showed that risk increased with the presence of nevi greater than 5 mm in diameter; light eyes, hair, and complexion; freckles; a history of skin cancer other than melanoma; a history of skin cancer in relatives; and maternal and paternal Northern or Central European ancestry. After adjustment for each other and for sun exposure factors, the phenotypic and host factors associated with all types of cutaneous malignant melanoma and superficial spreading melanoma were the presence of large nevi, light hair color, light complexion, and maternal Northern or Central European ancestry. Host factors associated with nodular melanoma after adjustment for other factors were the presence of large nevi, light hair color, ever being overweight by 20 pounds (9 kg) or more, and the presence of freckles.

Cutaneous melanoma in women. I. Exposure to sunlight, ability to tan, and other risk factors related to ultraviolet light

A population-based case-control study of cutaneous malignant melanoma (CMM) was conducted in 452 women with melanoma and 930 control subjects aged 25-59 years in five San Francisco Bay Area counties between 1981 and 1986. Women were interviewed in their homes with regard to history of sunlight exposure and sunburns during different periods in their lives, phenotypic and host characteristics, medical history, occupation, and demographic factors. Data were analyzed by the patients' histologic type of melanoma; 355 women were classified as having superficial spreading melanoma (SSM), 61 had nodular melanoma (NM), 13 had lentigo maligna melanoma, and 23 had other melanomas that could not be further classified upon histologic review by University of California dermatopathologists. Univariate results from analysis of factors related to sun exposure showed that the risk of all histologic types of CMM, SSM, and NM increased with increasing tendency of the subject to sunburn and with history of increased severity and/or frequency of sunburns up to age 12 years. Risk of all types of CMM and SSM also increased with increasing number of sunburns for all age groups and with lack of use of sunscreen. After adjustment for each other and for phenotypic factors, history of sunburn up to age 12 and lack of sunscreen use were the primary sun-related factors associated with an increased risk of all types of CMM and SSM, while tendency to sunburn when exposed to 1/2 hour of noontime sun and lack of use of sunscreen were related to NM. Although having frequent sunburns before age 12 and having severe sunburns before age 12 were both strongly associated with melanoma, having large numbers of sunburns during any time period from elementary school through age 30 years and having sunburns during the 10 years prior to diagnosis or interview were all associated with a doubling of risk for SSM after adjustment for other factors. These results suggest that the increased risk of melanoma related to sunburns is not confined to childhood sunburns. Maintenance of an all-year tan provided no protective effect against melanoma after adjustment for tendency to burn. No association was noted with use of fluorescent lights or exposure to sunlamps for all types of CMM, SSM, or NM.

Cutaneous melanoma in women. III. Reproductive factors and oral contraceptive use

Oral contraceptive use and reproductive factors were investigated in a population-based case-control study of 452 women aged 25-59 years who were diagnosed with cutaneous malignant melanoma during the period 1981-1986 and 930 controls. Ever use of oral contraceptives was reported by 72 percent of melanoma patients and 79 percent of control subjects in this San Francisco Bay Area study, although duration of use was slightly longer for women with superficial spreading melanoma (5.5 years) than for controls (4.3 years). While some subgroups had elevated or reduced odds ratios, no consistent association was observed between cutaneous melanoma risk and oral contraceptive use when use was examined by duration, latency, age at diagnosis, age at first use, and time period of first use. Neither number of live births nor age at birth of the first child was associated with risk for cutaneous melanoma; nor was a history of miscarriage, induced abortion, or endometriosis. No association was observed with regularity of menstrual periods or with use of fertility drugs or hormones to regulate menstrual periods. Women who reported experiencing hyperpigmentation of facial skin during a prior pregnancy had a lowered risk for all cutaneous melanoma (odds ratio (OR) = 0.64, 95% confidence interval (CI) 0.44-0.93) and superficial spreading melanoma (OR = 0.54, 95% CI 0.36-0.83). This effect was more pronounced for light-complexioned women (for superficial spreading melanoma, OR = 0.37, 95% CI 0.20-0.70) than for women with a dark or medium complexion (for superficial spreading melanoma, OR = 0.84, 95% CI 0.48-1.5). Women who reported use of acne medication also had a reduced risk of superficial spreading melanoma (OR = 0.55, 95% CI 0.35-0.84). These results indicate an overall lack of effect of oral contraceptives on cutaneous melanoma risk in this population of women. The reduced melanoma risks associated with hyperpigmentation during a prior pregnancy and use of acne medication (or related hormonal indications for its use) should be studied further.

Recognition and classification of clinically dysplastic nevi from photographs: a study of interobserver variation

The recognition of dysplastic nevi from photographs can aid in population surveys of nevi and in epidemiological studies of melanoma risk. The reproducibility of techniques for recognizing nevi as dysplastic or for scoring them according to the degree of dysplasia has not been measured. Using photographs of 300 nevi taken in the course of a case-control study of melanoma, we assessed the agreement among six clinicians in independently categorizing nevi as dysplastic and in grading the degree of dysplasia. On average, reviewers agreed with each other 77% of the time in classifying a nevus as dysplastic or normal. Pairwise agreement within one point on a six-point scale occurred 87% of the time on average. These results suggest that criteria for recognizing nevi as clinically dysplastic from photographs can be applied reproducibility.

Cutaneous melanoma in women: ovulatory life, menopause, and use of exogenous estrogens

Factors related to menopause and use of exogenous hormones other than p.o. contraceptives were examined in 452 women ages 25-59 who were diagnosed with cutaneous malignant melanoma. Control subjects for this population-based study in the San Francisco Bay Area were 930 women of the same age. An increased risk was observed for superficial spreading melanoma (SSM) in women who reached natural menopause after age 55 [odds ratio (OR), 3.6; 95% confidence interval (CI), 1.1-11.1], and for women who had had a bilateral oophorectomy within 9 years of their diagnosis with SSM (OR, 2.2; CI, 1.1-4.5). A somewhat elevated risk of melanoma after natural menopause or hysterectomy was no longer statistically significant after adjustment for exogenous hormone use. Prolonged use of p.o. exogenous hormones after hysterectomy for women who had retained at least one ovary was associated with an increased risk of SSM (OR, 5.4; CI, 1.5-19.3), and use of these products for fewer than 5 years after bilateral oophorectomy also was associated with an elevated risk of SSM (OR, 2.9; CI, 1.0-7.8). Conjugated estrogen use was associated with somewhat elevated risks for SSM after hysterectomy with one ovary retained (OR, 2.7; CI, 0.97-7.3) and after hysterectomy with bilateral oophorectomy (OR, 2.1; CI, 0.86-5.0). There was a suggestion of a trend for increased risk of SSM with increased dosage of conjugated estrogens after hysterectomy (P for trend = 0.07). Use of vaginal creams that contained estrogen also was associated with an increased risk of SSM (OR, 1.8; CI, 1.0-3.3).

Comparison of control subjects recruited by random digit dialing and area survey

Although random digit dialing (RDD) is an accepted and commonly used method of sampling populations for controls in case-control studies, there have been surprisingly few attempts to compare the accuracy of RDD with that of the best traditional alternative, i.e., household area surveys. The aim of the present study was to compare a variety of characteristics of control subjects selected by RDD and area survey methods. All data were gathered through in-person interviews of both types of control subjects. The area survey identified a population-based sample of 20- to 79-year-old residents of two Washington State counties in 1978 and 1979. Control groups for three case-control studies of bladder cancer, gynecologic cancers, and multiple myeloma were drawn from this area sample, for a total of 240 control subjects. Controls aged 21-64 years from the same counties were identified for the National Bladder Cancer Study using RDD telephone sampling during the same time period. There were 134 respondents in the RDD control group. Overall, the two control groups selected by these two different methods yielded similar estimated frequencies of various population characteristics. The small differences observed in some age/sex subgroups and the statistical significance of the overall measure of association for occupational exposure to organic substances may be attributed to multiple comparisons.

Contraceptive use among women smokers and nonsmokers in the San Francisco Bay area

BACKGROUND

Women smokers were previously reported to be more sexually active but less likely to use contraception than nonsmokers. Differences in contraceptive choices between the two groups were investigated.

METHODS

Sexually active women, 287 who smoked cigarettes and 263 who did not smoke, were queried about current contraceptive use and demographic, sexual, and reproductive factors.

RESULTS

Sexually active smokers were less likely than nonsmokers to use contraceptives, especially oral contraceptives. The deficit of contraceptive use among smokers was most pronounced in women under age 30, black women, single women, women with some college education, nulliparous women, women who reported early age at first intercourse, and women who reported four or more lifetime sexual partners. In contrast, smokers were more than twice as likely as nonsmokers to use sterilization (P = 0.002). Among women over age 30, prevalence of contraceptive use was similar between the two groups. Oral contraceptives were used by fewer smokers than nonsmokers who were under age 24 (P = 0.01), had a high school education or less (P = 0.01), and/or had never been pregnant (P = 0.03).

CONCLUSIONS

Young, sexually active women who smoked cigarettes were less likely than nonsmokers to have used contraceptives, especially oral contraceptives, while women smokers over age 30 were more likely than nonsmokers to have used sterilization.

Characteristics of women nonsmokers exposed to passive smoke

BACKGROUND

Studies that have investigated the association between exposure to passive smoke and increased risk for disease have had inconclusive results and have raised questions about whether women exposed to passive smoke differ from those not exposed.

METHODS

The study population included 120 women nonsmokers who reported that they had been exposed to passive smoke in the 24 hr prior to the interview and 213 women who reported no exposure. Women were queried about demographic, lifestyle, sexual, and reproductive factors.

RESULTS

Exposed women were younger, less educated, and slightly heavier than nonexposed women. They were more likely to be divorced or separated (OR = 3.3, 95% CI = 1.4-7.6, P = 0.005), to have had first intercourse at or before age 16 (OR = 1.4, 95% CI = 1.0-1.9, P = 0.04), and to have had three or more live births (OR = 2.9, 95% CI = 1.2-6.8, P = 0.02). Women exposed to passive smoke were more likely to have consumed two or more cups of coffee (OR = 2.0, 95% CI = 1.1-3.8, P = 0.03), two or more glasses of beer (OR = 3.7, 95% CI = 1.1-12.5, P = 0.03), or to have smoked marijuana in the past 24 hr (OR = 14.7, 95% CI = 1.8-122.3, P = 0.01) than women who were not exposed. There were no differences noted between exposed and nonexposed women in history of gynecologic diseases or number of cervical microorganisms.

CONCLUSION

Women exposed to passive smoke differed from those not exposed on several factors that should be considered in future studies that seek to investigate smoking-related disease risk.

Detection of mutagens in cervical mucus in smokers and nonsmokers

The Salmonella mutagenicity test was used to analyze cervical mucus specimens from 364 smokers and 333 nonsmokers to determine whether the association between smoking and mutagenic cervical mucus that we reported previously among women diagnosed with dysplasia would apply to a larger group of healthy women (E. A. Holly et al., J. Natl. Cancer Inst., 76: 983-986, 1986). Women smokers and nonsmokers between the ages of 18 and 49 who attended eleven clinics and physicians' offices in the San Francisco Bay area for a routine Pap smear were examined to determine whether smokers were more likely to have mutagenic substances in their cervical mucus. About 4% of smokers and 8% of nonsmokers had positive mutagenicity test results (P = 0.02). Cervical mucus with a large number of microorganisms was more likely to have a positive mutagenicity test result than that with fewer microorganisms (test for trend, P = 0.01). Mutagenicity results varied by race and clinic location but were not associated with smoking behavior, sexual behavior, gynecological diagnosis, or diet. Further work is needed to develop methods to detect mutagens in specific body fluids.

Natural history of anal cytologic abnormalities and papillomavirus infection among homosexual men with group IV HIV disease

Previous studies have demonstrated a high prevalence of anal cytologic abnormalities as well as anal human papillomavirus (HPV) infection among homosexual men with group IV HIV disease. However, the natural history of these changes in this population has not yet been studied. To this end, 37 homosexual men with group IV HIV disease attending an outpatient HIV clinic were followed at approximately 9-month intervals for an average of 17 months, using anal cytology, anoscopy, anal biopsy, and anal HPV DNA hybridization. During the study, the proportion of the 37 subjects with anal cytologic abnormalities increased from 27 to 65%. The proportion of subjects with any grade of anal intraepithelial neoplasia rose from 8 to 32%, with high-grade anal intraepithelial neoplasia increasing from 0 to 16%. The proportion of subjects with anal HPV infection increased from 60 to 89%, and infection with multiple HPV types was noted in at least 48%. We conclude that a large proportion of homosexual men with group IV HIV disease develop anal cytologic abnormalities, including anal intraepithelial neoplasia, over a short period of time. Together with a rapidly increasing incidence of anal cancer among single, never-married men in the San Francisco Bay area, these results suggest that these men may be at significant risk of development of anal cancer.

Characteristics of women by smoking status in the San Francisco Bay Area

To better understand why smokers are more likely to develop cervical cancer than nonsmokers, we investigated laboratory and demographic differences between the two groups. Women between the ages of 18 and 49 who attended eleven community clinics in the San Francisco Bay Area were studied to investigate differences between smokers and nonsmokers. The 332 smokers and 365 nonsmokers were queried about smoking habits, sexual and reproductive history, and recent diet. Cervical mucus specimens were cultured for yeast, lactobacillus, and other microorganisms. Results showed that white Hispanic women were less likely to smoke than white non-Hispanic women. Smokers, when compared to nonsmokers, consumed larger quantities of coffee, soft drinks, liquor, and beer in the 24 h prior to the interview. Women who smoked were more likely than those who did not smoke to have had first sexual intercourse before age 16, had a greater number of lifetime sexual partners, and were more likely than nonsmokers to have been pregnant. After controlling for number of sexual partners, smokers reported a history of chlamydia, gonorrhea, and/or pelvic inflammatory disease more often than did nonsmokers, and cervical mucus of smokers was more likely than that from nonsmokers to contain greater than 8500 microorganisms/ml.

Ewing's bone sarcoma, paternal occupational exposure, and other factors

To determine risk factors for Ewing's bone sarcoma, the authors interviewed mothers of 43 patients diagnosed between January 1978 and August 1986 and 193 controls in the San Francisco Bay Area, California, regarding medical and occupational history of parents and other factors related to the subjects and their immediate families. Controls were selected by using random digit dial telephone methods. Adjusted relative risk estimates suggest that risks were elevated for children whose fathers were engaged in agricultural occupations during the period from 6 months prior to conception of the subject up to the time of diagnosis for the patients or interview for the controls (relative risk (RR) = 8.8, 95% confidence interval (CI) 1.8-42.7) and for children whose fathers had occupational exposure to herbicides, pesticides, or fertilizers (RR = 6.1, 95% CI 1.7-21.9, p = 0.002). Prior ingestion of poison or an overdose of medication was more common in patients than in controls (RR = 4.4, 95% CI 1.4-13.5). These and other findings should be investigated in larger population-based studies to determine specific factors that may account for the associations.