Formaldehyde and cancer risk: a quantitative review of cohort studies through 2006.

BACKGROUND: Occupational exposure to formaldehyde has been associated with excess risk of nasopharyngeal and selected other cancers. PATIENTS AND METHODS: We reviewed and pooled the results of cohort studies published through February 2007. RESULTS: There were 5651 deaths from all cancers observed in six cohorts of industry workers and six of professionals, with a pooled relative risk (RR) of 0.95 for industry workers and of 0.87 for professionals. Nine deaths from nasopharyngeal cancer in three cohorts of industry workers yielded a pooled RR of 1.33, which declined to 0.49 after excluding six cases from one US plant. The pooled RR for lung cancer was 1.06 in industry workers and 0.63 in professionals. Corresponding values were 1.09 and 0.96 for oral and pharyngeal, 0.92 and 1.56 for brain, 0.85 and 1.31 for all lymphatic and hematopoietic cancers, and 0.90 and 1.39 for leukemia. CONCLUSIONS: Comprehensive review of cancer in industry workers and professionals exposed to formaldehyde shows no appreciable excess risk for oral and pharyngeal, sinonasal or lung cancers. A non-significantly increased RR for nasopharyngeal cancer among industry workers is attributable to a cluster of deaths in a single plant. For brain cancer and lymphohematopoietic neoplasms there were modestly elevated risks in professionals, but not industry workers.

COX-2-selective inhibitors and the risk of upper gastrointestinal bleeding in high-risk patients with previous gastrointestinal diseases: a population-based case-control study.

BACKGROUND: Clinical trials have suggested that cyclo-oxygenase-2-selective inhibitors are associated with a lower risk of upper gastrointestinal bleeding than are non-selective, non-aspirin, non-steroidal anti-inflammatory drugs. This has not yet been confirmed in studies of patients with an increased susceptibility to upper gastrointestinal bleeding. AIM: To examine the risk of upper gastrointestinal bleeding in high-risk patients who filled prescriptions for cyclo-oxygenase-2 inhibitors or other non-steroidal anti-inflammatory drugs. METHODS: A population-based case-control study was performed in the Danish county of North Jutland from 1 January 2000 to 31 December 2002. From the County Hospital Discharge Registry and the Civil Registration System, we identified incident cases with upper gastrointestinal bleeding (n = 780) and randomly selected controls (n = 2906), respectively. All cases and controls had previous gastrointestinal diseases. Data on drug exposure were obtained from the countywide Prescription Database. RESULTS: Thirty-five cases (4.5%) filled prescriptions for cyclo-oxygenase-2 inhibitors within 30 days of the date of upper gastrointestinal bleeding, compared with 79 controls (2.7%). Adjusted odds ratios for upper gastrointestinal bleeding according to prescription for celecoxib, rofecoxib and non-steroidal anti-inflammatory drugs were 1.3 [95% confidence interval (CI), 0.7-2.8], 2.1 (95% CI, 1.2-3.5) and 3.3 (95% CI, 2.4-4.4), respectively. CONCLUSIONS: In patients with increased susceptibility to gastrointestinal adverse events, a lower risk of upper gastrointestinal bleeding was observed in users of cyclo-oxygenase-2 inhibitors compared with users of other non-aspirin, non-steroidal anti-inflammatory drugs.

Magnetic fields produced by hand held hair dryers, stereo headsets, home sewing machines, and electric clocks.

A recent epidemiologic study reported associations between leukemia risk in children and their personal use of television (TV) sets, hair dryers, and stereo headsets, and the prenatal use by their mothers of sewing machines. To provide exposure data to aid in the interpretation of these findings, extremely and very low frequency (ELF and VLF) magnetic fields produced by a sample of each type of appliance were characterized in a field study of volunteers conducted in Washington DC and its Maryland suburbs. Questionnaire data regarding children's or mothers' patterns of usage of each type of appliance were also collected. ELF magnetic fields measured 10 cm from the nozzles of hair dryers were elevated over the ambient by a mean factor of 17 when these devices were in use. Fields near headsets being used to listen to music were not distinguishable from ambient levels except at frequencies below and well above 60 Hz and, even then, field levels were < 0.01 microT. Home sewing machines produced ELF magnetic fields that were elevated by a factor of 2.8 over ambient levels at the front surfaces of the lower abdomens of mothers. Estimated mean daily times of usage of hair dryers, stereo headsets, and sewing machines were 2.6, 19, and 17 minutes, respectively. These data and previously published data on TV sets, do not provide a consistent picture of increased (or decreased) leukemia risk in relation to increasing peak or time weighted average (TWA) ELF magnetic field exposure. The data could, however, conceivably be compatible with some more complex biophysical model with unknown properties. Overall, the results of this study provide little evidence supporting the hypothesis that peak or TWA ELF magnetic fields produced by appliances are causally related to the risk of childhood leukemia in children.

A single nucleotide polymorphism in the 5' untranslated region of RAD51 and risk of cancer among BRCA1/2 mutation carriers.

RAD51 colocalizes with both BRCA1 and BRCA2, and genetic variants in RAD51 would be candidate BRCA1/2 modifiers. We searched for RAD51 polymorphisms by sequencing 20 individuals. We compared the polymorphism allele frequencies between female BRCA1/2 mutation carriers with and without breast or ovarian cancer and between population-based ovarian cancer cases with BRCA1/2 mutations to cases and controls without mutations. We discovered two single nucleotide polymorphisms (SNPs) at positions 135 g-->c and 172 g-->t of the 5' untranslated region. In an initial group of BRCA1/2 mutation carriers, 14 (21%) of 67 breast cancer cases carried a "c" allele at RAD51:135 g-->c, whereas 8 (7%) of 119 women without breast cancer carried this allele. In a second set of 466 mutation carriers from three centers, the association of RAD51:135 g-->c with breast cancer risk was not confirmed. Analyses restricted to the 216 BRCA2 mutation carriers, however, showed a statistically significant association of the 135 "c" allele with the risk of breast cancer (adjusted odds ratio, 3.2; 95% confidence limit, 1.4-40). BRCA1/2 mutation carriers with ovarian cancer were only about one half as likely to carry the RAD51:135 g-->c SNP. Analysis of the RAD51:135 g-->c SNP in 738 subjects from an Israeli ovarian cancer case-control study was consistent with a lower risk of ovarian cancer among BRCA1/2 mutation carriers with the "c" allele. We have identified a RAD51 5' untranslated region SNP that may be associated with an increased risk of breast cancer and a lower risk of ovarian cancer among BRCA2 mutation carriers. The biochemical basis of this risk modifier is currently unknown.

Static magnetic field measurements in residences in relation to resonance hypotheses of interactions between power-frequency magnetic fields and humans.

Bowman et al. used epidemiologic data to test a model in which subjects were classified as being "in-resonance" or "not-in-resonance" for 60-Hz magnetic-field exposures depending on single static magnetic-field measurements at the centers of their bedrooms. A second paper by Swanson concluded that a single static magnetic-field measurement is insufficient to meaningfully characterize a residential environment. The main objective of this study was to investigate exposure-related questions raised by these two papers in two U.S. data sets, one containing single spot measurements of static magnetic fields at two locations in homes located in eight states, and the other repeated spot measurements (seven times during the course of one year) of the static magnetic fields at the centers of bedrooms and family rooms and on the surfaces of beds in 51 single-family homes in two metropolitan areas. Using Bowman's criterion, bedrooms were first classified as being in-resonance or not-in-resonance based on the average of repeated measurements of the static magnetic field measured on the bed where the presumed important exposure actually occurred. Bedrooms were then classified a second time using single spot measurements taken at the centers of bedrooms, centers of family rooms, or on the surfaces of beds, as would be done in the typical epidemiologic study. The kappa statistics characterizing the degree of concordance between the first (on-bed averages) and second (spot measurements) methods of assessing resonance status were 0.44, 0.33, and 0.67, respectively. This level of misclassification could significantly affect the results of studies involving the determination of resonance status.

Biomarker correlations of urinary 2,4-D levels in foresters: genomic instability and endocrine disruption.

Forest pesticide applicators constitute a unique pesticide use group. Aerial, mechanical-ground, and focal weed control by application of herbicides, in particular chlorophenoxy herbicides, yield diverse exposure scenarios. In the present work, we analyzed aberrations in G-banded chromosomes, reproductive hormone levels, and polymerase chain reaction-based V(D)J rearrangement frequencies in applicators whose exposures were mostly limited to chlorophenoxy herbicides. Data from appliers where chlorophenoxy use was less frequent were also examined. The biomarker outcome data were compared to urinary levels of 2,4-dichlorophenoxyacetic acid (2,4-D) obtained at the time of maximum 2,4-D use. Further comparisons of outcome data were made to the total volume of herbicides applied during the entire pesticide-use season.Twenty-four applicators and 15 minimally exposed foresters (control) subjects were studied. Categorized by applicator method, men who used a hand-held, backpack sprayer in their applications showed the highest average level (453.6 ppb) of 2,4-D in urine. Serum luteinizing hormone (LH) values were correlated with urinary 2,4-D levels, but follicle-stimulating hormone and free and total testosterone were not. At the height of the application season; 6/7 backpack sprayers, 3/4 applicators who used multinozzle mechanical (boom) sprayers, 4/8 aerial applicators, and 2/5 skidder-radiarc (closed cab) appliers had two or more V(D)J region rearrangements per microgram of DNA. Only 5 of 15 minimally exposed (control) foresters had two or more rearrangements, and 3 of these 5 subjects demonstrated detectable levels of 2,4-D in the urine. Only 8/24 DNA samples obtained from the exposed group 10 months or more after their last chlorophenoxy use had two rearrangements per microgram of DNA, suggesting that the exposure-related effects observed were reversible and temporary. Although urinary 2,4-D levels were not correlated with chromosome aberration frequency, chromosome aberration frequencies were correlated with the total volume of herbicides applied, including products other than 2,4-D. In summary, herbicide applicators with high urinary levels of 2,4-D (backpack and boom spray applications) exhibited elevated LH levels. They also exhibited altered genomic stability as measured by V(D)J rearrangement frequency, which appears reversible months after peak exposure. Though highly detailed, the limited sample size warrants cautious interpretation of the data.

Third complementarity-determining region of mutated VH immunoglobulin genes contains shorter V, D, J, P, and N components than non-mutated genes.

The third complementarity-determining region (CDR3) of immunoglobulin variable genes for the heavy chain (VH) has been shown to be shorter in length in hypermutated antibodies than in non-hypermutated antibodies. To determine which components of CDR3 contribute to the shorter length, and if there is an effect of age on the length, we analysed 235 cDNA clones from human peripheral blood of VH6 genes rearranged to immunoglobulin M (IgM) constant genes. There was similar use of diversity (D) and joining (JH) gene segments between clones from young and old donors, and there was similar use of D segments among the mutated and non-mutated heavy chains. However, in the mutated heavy chains, there was increased use of shorter JH4 segments and decreased use of longer JH6 segments compared to the non-mutated proteins. The overall length of CDR3 did not change with age within the mutated and non-mutated categories, but was significantly shorter by three amino acids in the mutated clones compared to the non-mutated clones. Analyses of the individual components that comprise CDR3 indicated that they were all shorter in the mutated clones. Thus, there were more nucleotides deleted from the ends of VH, D, and JH gene segments, and fewer P and N nucleotides added. The results suggest that B cells bearing immunoglobulin receptors with shorter CDR3s have been selected for binding to antigen. A smaller CDR3 may allow room in the antibody binding pocket for antigen to interact with CDRs 1 and 2 as well, so that as the VDJ gene undergoes hypermutation, substitutions in all three CDRs can further contribute to the binding energy.

Impact of age on hypermutation of immunoglobulin variable genes in humans.

Chronological aging is associated with an accumulation of DNA mutations that results in cancer formation. The effect of aging on spontaneous mutations in humans is difficult to study because mutations are infrequent in the overall genome and tumors are relatively rare. In contrast, somatic mutations in immunoglobulin variable genes are abundant and can be studied in peripheral blood lymphocytes. To determine if aging alters the frequency and pattern of hypermutation, we sequenced 331 cDNA clones with rearranged V(H)6 genes and compared 452 mutations from young humans to 570 mutations from old humans. There were more mutated clones in the young population compared to the old population. Among the mutated clones, the frequency, location, and types of substitutions were similar between the young and the old groups. However, the ratio of replacement-to-silent mutations was much higher in the complementarity-determining regions of heavy chains from old people, which indicates that their B cells had been selected by antigen. Among individuals, there was variability in the frequency of tandem mutations, which we have observed in mice defective for the PMS2 mismatch repair protein. Microsatellite variability in DNA, which is caused by impaired mismatch repair, was then measured, and there was a strong correlation between the frequency of tandem mutations and microsatellite alterations. The data suggest that individuals vary in their mismatch repair capacity, which can affect the mutational spectra in their antibodies.

Household solvent exposures and childhood acute lymphoblastic leukemia.

OBJECTIVES: This study explored the risk of childhood acute lymphoblastic leukemia (ALL) associated with participation by household members in hobbies or other home projects involving organic solvents. METHODS: Participants in this case-control study were 640 subjects with ALL and 640 matched controls. RESULTS: Childhood ALL was associated with frequent (> 4 times/month) exposure to model building (odds ratio [OR] = 1.9; 95% confidence interval [95% CI] = 0.7, 5.8) and artwork using solvents (OR = 4.1; 95% CI = 1.1, 15.1). We also found elevated risk (OR = 1.7; 95% CI = 1.1, 2.7) among children whose mothers lived in homes painted extensively (> 4 rooms) in the year before the children's birth. CONCLUSIONS: In this exploratory study, substantial participation by household members in some common household activities that involve organic solvents was associated with elevated risks of childhood ALL.

Recent trends in lung cancer mortality in the United States.

BACKGROUND: Previous age-period-cohort analyses of lung cancer incidence and mortality rates in the United States have demonstrated a decrease in risk by birth cohort through 1950, consistent with declining trends in smoking prevalence. This study was conducted to examine recent lung cancer trends, including trends among the cohorts born after 1950. METHODS: Lung cancer mortality rates from 1970 through 1997 for whites aged 24--83 years and for blacks aged 30--83 years were investigated. Using age--period--cohort analyses with 2-year age and 2-year calendar-period intervals, we examined changes in the slope of the trends in birth-cohort and calendar-period effects. All statistical tests are two-sided. RESULTS: There was an unexpected, statistically significant moderation in the rate of decrease of the birth-cohort trend in lung cancer mortality for whites born after 1950, with a corresponding smaller and statistically nonsignificant moderation for blacks. These data are consistent with smoking initiation rates: Rates of both cigarette and marijuana smoking initiation increased for children aged 12--17 years from 1965 through 1977. There was a statistically significant decrease in the slope of the calendar-period trend for lung cancer mortality in 1990 for both whites and blacks that was observed primarily in people 55 years of age and older. CONCLUSIONS AND IMPLICATIONS: The birth-cohort pattern of lung cancer mortality after 1950 appears to reflect the early impact of teenage cigarette smoking on lung cancer risk in people under the age of 45 years, although a contribution from marijuana smoking cannot be ruled out. This result provides additional support for increasing smoking cessation and prevention programs for teenagers. The calendar-period decrease in lung cancer mortality after 1990 may reflect the long-term benefits of reductions in tobacco carcinogens in cigarettes and increases in smoking cessation beginning around 1960.

Cellular-telephone use and brain tumors.

BACKGROUND: Concern has arisen that the use of hand-held cellular telephones might cause brain tumors. If such a risk does exist, the matter would be of considerable public health importance, given the rapid increase worldwide in the use of these devices. METHODS: We examined the use of cellular telephones in a case-control study of intracranial tumors of the nervous system conducted between 1994 and 1998. We enrolled 782 patients through hospitals in Phoenix, Arizona; Boston; and Pittsburgh; 489 had histologically confirmed glioma, 197 had meningioma, and 96 had acoustic neuroma. The 799 controls were patients admitted to the same hospitals as the patients with brain tumors for a variety of nonmalignant conditions. RESULTS: As compared with never, or very rarely, having used a cellular telephone, the relative risks associated with a cumulative use of a cellular telephone for more than 100 hours were 0.9 for glioma (95 percent confidence interval, 0.5 to 1.6), 0.7 for meningioma (95 percent confidence interval, 0.3 to 1.7), 1.4 for acoustic neuroma (95 percent confidence interval, 0.6 to 3.5), and 1.0 for all types of tumors combined (95 percent confidence interval, 0.6 to 1.5). There was no evidence that the risks were higher among persons who used cellular telephones for 60 or more minutes per day or regularly for five or more years. Tumors did not occur disproportionately often on the side of head on which the telephone was typically used. CONCLUSIONS: These data do not support the hypothesis that the recent use of hand-held cellular telephones causes brain tumors, but they are not sufficient to evaluate the risks among long-term, heavy users and for potentially long induction periods.

Nonparametric evaluation of birth cohort trends in disease rates.

BACKGROUND: Although interpretation of age-period-cohort analyses is complicated by the non-identifiability of maximum likelihood estimates, changes in the slope of the birth-cohort effect curve are identifiable and have potential aetiologic significance. METHODS: A nonparametric test for a change in the slope of the birth-cohort trend has been developed. The test is a generalisation of the sign test and is based on permutational distributions. A method for identifying interactions between age and calendar-period effects is also presented. RESULTS: The nonparametric method is shown to be powerful in detecting changes in the slope of the birth-cohort trend, although its power can be reduced considerably by calendar-period patterns of risk. The method identifies a previously unidentified decrease in the birth-cohort risk of lung-cancer mortality from 1912 to 1919, which appears to reflect a reduction in the initiation of smoking by young men at the beginning of the Great Depression (1930s). The method also detects an interaction between age and calendar period in leukemia mortality rates, reflecting the better response of children to chemotherapy. CONCLUSION: The proposed nonparametric method provides a data analytic approach, which is a useful adjunct to log-linear Poisson analysis of age-period-cohort models, either in the initial model building stage, or in the final interpretation stage.

Implications of stage-specific survival rates in assessing recent declines in prostate cancer mortality rates.

It has been noted that the most important evidence for a benefit of early detection of prostate cancer using prostate-specific antigen (PSA) testing would be a decline in prostate cancer mortality rates to levels below those existing before diagnostic use of PSA testing. We document a decrease in U.S. prostate cancer mortality rates in white men less than 85 years of age to levels below those existing in 1986, the year use of PSA testing was approved. In fact, for men 60-79 years of age, prostate cancer mortality rates were lower in 1997 than in any year since 1950. Although it has been argued that the decrease in prostate cancer mortality rates began too soon to be explained by PSA testing, stage-specific survival rates indicate that a rapid decrease in mortality may be explained by the large number of high-grade prostate cancers detected before metastasis. If recent decreases in U.S. prostate cancer mortality rates are due to early detection using PSA testing, randomized clinical trials investigating PSA testing will show early evidence of a mortality benefit.

Do confounding or selection factors of residential wiring codes and magnetic fields distort findings of electromagnetic fields studies?

In contrast with several previous studies, our recent large case-control study found little association between childhood acute lymphoblastic leukemia (ALL) and electric-power-line wire codes. Here we examine internal evidence from our study to assess the possibility that selection bias and/or confounding may have affected the findings. We compared the relation between childhood ALL and wire codes and direct measurements of magnetic fields in subjects who participated in all phases of the study with the relation in all subjects, including those who declined to allow access inside the home. We found that the odds ratio for ALL among those living in homes with very high current configurations increased by 23% when 107 "partial participants" were excluded. We found similar, but slightly smaller, increases in the odds ratios when we performed the same comparisons using direct measurements of magnetic fields, excluding subjects who allowed only a measurement outside the front door. "Partial participants" tended to be characterized by lower socioeconomic status than subjects who participated fully, suggesting possible selection bias. We also examined the relation between a large number of potential confounding variables and both proxy and direct measurements of magnetic fields. Univariate adjustment for individual variables changed the odds ratio for ALL by less than 8%, while simultaneous adjustment for several factors reduced the estimate by a maximum of 15%. We conclude that while confounding alone is unlikely to be an important source of bias in our own and previous studies of magnetic fields, selection bias may be more of a concern, particularly in light of the generally low response rates among controls in case-control studies.

A new xeroderma pigmentosum group C poly(AT) insertion/deletion polymorphism.

We found a common biallelic polymorphism (PAT) in the xeroderma pigmentosum complementation group C (XPC) DNA repair gene consisting of an insertion of 83 bases of A and T [poly(AT)] and a 5 base deletion within intron 9. We developed a PCR assay to resolve the XPC PAT+ and PAT- alleles and found that the PAT+ allele frequency was 0.44 in 156 cancer-free donors from the Johns Hopkins School of Public Health, 0.41 in 263 cancer-free donors from the Baltimore Longitudinal Study of Aging and 0.36 in samples from 216 unselected donors from NIH. We also found a single nucleotide polymorphism in exon 15 of the XPC gene (A2920C, Lys939-->Gln) that creates a new enzyme restriction site. This XPC exon 15 single nucleotide polymorphism occurred at a frequency of 0.38 in 98 NIH donors and is in linkage disequilibrium with the PAT locus. We developed an allele-specific complementation assay utilizing post-UV host cell reactivation to assess DNA repair capacity of polymorphic alleles. We found similar DNA repair with XPC 2920A and XPC 2920C. These common polymorphisms in the XPC DNA repair gene may be useful for molecular epidemiological studies of cancer susceptibility.

Age-period-cohort analyses of breast-, ovarian-, endometrial- and cervical-cancer mortality rates for Caucasian women in the USA.

BACKGROUND: Age-period-cohort analyses of US breast-cancer mortality rates reveal an unexpected decrease in risk for women born after 1948. Hormones are thought to play an important role in the aetiology of breast cancer and female gynaecologic cancers, and thus the evaluation of birth-cohort trends for female gynaecologic cancers may shed light on the declining breast-cancer risk among 'baby-boomers'. METHODS: Age-period-cohort analyses are applied to US mortality rates for breast cancer, ovarian cancer, endometrial cancer and cervical cancer from 1950 through 1995. RESULTS: Age-period-cohort analyses provide no clues regarding the declining birth-cohort risk for breast cancer in 'baby-boomers'. The birth-cohort curves for ovarian and endometrial cancers are roughly similar, and largely explained by known risk factors. The calendar-period curve for endometrial cancer reveals increased risk between 1960 and 1980, probably due to increased use of oestrogen replacement therapy. Changes in the birth-cohort curve for cervical cancer reflect, for the most part, changes in sexual activity. An unexpected significant increase in the calendar-period curve for ovarian cancer occurred around 1980. CONCLUSION: Most of the major changes in the calendar-period and birth-cohort curves for breast cancer and female gynaecologic cancers can be explained by documented changes in known risk factors and in medical practice. The decreasing breast-cancer birth-cohort risk among 'baby-boomers' and the increasing ovarian-cancer calendar-period curve after 1980 are recent changes that require further investigation.

Extremely low-frequency magnetic fields and childhood acute lymphoblastic leukemia: an exploratory analysis of alternative exposure metrics.

Data collected by the National Cancer Institute-Children's Cancer Group were utilized to explore various metrics of magnetic field levels and risk of acute lymphoblastic leukemia (ALL) in children. Cases were aged 0-14 years, were diagnosed with ALL during 1989-1993, were registered with the Children's Cancer Group, and resided in one home for at least 70 percent of the 5 years immediately prior to diagnosis. Controls were identified by using random digit dialing and met the same residential requirements. With 30-second ("spot") measurements and components of the 24-hour measurement obtained in the subject's bedroom, metrics evaluated included measures of central tendency, peak exposures, threshold values, and measures of short-term temporal variability. Measures of central tendency and the threshold measures showed good-to-high correlation, but these metrics correlated less well with the others. Small increases in risk (ranging from 1.02 to 1.69 for subjects in the highest exposure category) were associated with some measures of central tendency, but peak exposures, threshold values, measures of short-term variability, and spot measurements demonstrated little association with risk of childhood ALL. In general, risk estimates were slightly higher for the nighttime (10 p.m.-6 a.m.) interval than for the corresponding 24-hour period.

Increased lymphocyte replicative index following 2,4-dichlorophenoxyacetic acid herbicide exposure.

OBJECTIVE: Evaluate peripheral blood lymphocyte proliferation (replicative index:RI) and micronuclei frequency (MF) among 2,4-D herbicide applicators. METHODS: Twelve applicators spraying only 2,4-D provided a blood and urine specimen upon enrollment, several urine samples during the spraying season, and a blood specimen at the study's end. Nine controls provided blood and urine specimens upon enrollment and at the study's end. Gas chromatography/tandem mass spectroscopy determined urinary 2,4-D levels and standard in-vitro assays determined RI and MF scores. Applicator RI and MF were compared before and after spraying and with controls. RESULTS: Applicators contributed 45 urine specimens with concentrations ranging from 1.0 to 1700 (microg 2,4-D/g creatinine/L urine) that logarithmically (In) increased as spraying time increased. Applicator RI increased after spraying (p = 0.016), independent of tobacco and alcohol use, and demonstrated a weak dose-response with increasing urinary 2,4-D levels (p = 0.15). Among 2,4-D applicators, pre-exposure complete blood counts and lymphocyte immunophenotypes were not significantly different from post-exposure measurements. CONCLUSION: Urinary 2,4-D concentration, an exposure biomarker, may be associated with lymphocyte replicative index, a cell proliferation biomarker.