
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Divisions of Cancer Epidemiology and Genetics [D. B., N. R., A. M., R. E. T., P. H.] and Clinical Sciences [L. K., W. W.], National Cancer Institute, Bethesda, Maryland 20892-7240
| Abstract |
|---|
|
|
|---|
| Introduction |
|---|
|
|
|---|
To assess the contribution of organochlorine exposure in the general population to risk of NHL, large studies are needed. Because DDT and PCB exposure in the general population cannot be assessed by questionnaire alone, biological measurement of these compounds is essential. Although case-control studies nested within prospective cohorts are ideal to assess this question, many cohort studies will not have a large enough number of NHL cases to be able to address this issue. Furthermore, if organochlorines contribute to the etiology of NHL, they may function as promoters via their suggested immune-modulating properties (8) . If so, assessing exposure levels close to the time of NHL diagnosis becomes important, another limitation of cohort studies where most cases are diagnosed years after enrollment. Finally, disentangling the effects of PCBs, DDE, dioxins, and other organochlorines requires relatively large serum volumes that are generally unavailable in prospective cohort studies.
For all of these reasons, large population-based case-control studies of NHL will be a likely choice to study the organochlorine-NHL hypothesis. In many case-control studies, cases are enrolled after treatment has begun; therefore, it is critical to determine whether disease onset or treatment alters organochlorine levels. Disease effects can be assessed indirectly by studying organochlorine levels in a range of cases that vary by stage/grade and the presence or absence of clinical symptoms. Treatment effects can be assessed by studying patients before and after the initiation of chemotherapy.
We used a preexisting collection of paired serum samples from 22 cases to assess the effects of treatment on organochlorine levels.
| Materials and Methods |
|---|
|
|
|---|
Assay Methods for DDE and PCBs.
Randomly numbered serum samples were stored below -70°C.
Laboratory analyses were conducted in blinded pretreatment and
posttreatment pairs of the subjects assayed in the same batch. One ml
of thawed serum was transferred by pipette to a centrifuge tube, and
the volume of the serum was recorded to ±0.01 ml. Ten ng of a
surrogate PCB (PCB-198) was added to the serum. One ml of methanol was
added to denature albumin. The mixture was extracted three times with 5
ml of 50% ethyl ether:n-hexane, and the extracts were
combined and concentrated to 10.0 ml. Two ml of this extract were
removed for lipid determination. The remaining 8 ml were concentrated
to 1 ml and transferred to 1 g of Florisil SPE column, and the
pesticides and PCBs were eluted with 10 ml of n-hexane
(fraction 1), followed by 10 ml of 1% ethyl ether in
n-hexane (fraction 2). The fractions were concentrated to
1.0 ml, spiked with 10 ng of internal standard (PCB-119), and analyzed
by gas chromatography with electron capture detection. Gas
chromatography with electron capture detection was calibrated by
repetitive analysis of standard mixtures of selected individual PCB
congeners at six levels for the quantification of individual congener
and total PCB levels. The analysis method for individual PCB congeners
was a modified version of established methods (9, 10, 11, 12, 13)
. The
total PCB level in each sample was also determined by summing the
individual PCB congener levels. The procedure for determining the total
PCB levels was validated by comparing to the Webb-McCall method
(14)
.
We limited our analysis to PCB-138, PCB-153, and PCB-156 because these congeners were among those showing higher serum concentrations and a lower percentage of samples below the detection limit. The limit of detection was 0.2 ng/ml for DDE and 0.05 ng/ml for individual PCBs congeners and total PCBs. There were two subjects with DDE levels below the detection limit and six subjects with PCB-156 levels below the detection limit. For purposes of computation, we replaced the undetectable values by half of the values of the detection limits. The coefficients of variation for the DDE and PCB assays ranged from 35 to 49%.
Lipid Determination.
One-g aluminum pans were embossed with labels and dried in an oven at
105°C for 1 h, allowed to cool in a desiccator, and then weighed
to ±0.00001 g. Two ml of serum extract were transferred to each pan
with n-hexane rinses. The pans were allowed to air dry,
protected from dust, and then heated to 105°C and held at that
temperature for 15 min. The pans were allowed to cool in a desiccator
and then reweighed. Several empty (blank) pans were run simultaneously
to check for method bias. The method for the total lipid analysis was
adopted from the methods used by Sheldon (15
, 16)
.
We calculated lipid-corrected values by dividing serum levels of chemicals by the total lipid value. To calculate the total lipid-corrected PCB levels, we divided each congener by the total lipid value and summed them.
Statistical Analysis.
Pretreatment and posttreatment organochlorine serum levels were
compared using Pearson correlation coefficient (r), paired
t tests, and sign tests (17)
. Two sided
Ps are reported for all comparisons.
| Results |
|---|
|
|
|---|
5% (P =
0.012) and a nonsignificant increase in total lipid levels of
6.5%
(P = 0.17).
|
|
|
|
|
|
|
| Discussion |
|---|
|
|
|---|
It is unlikely that secular trends could explain the decline observed during the interval between pretreatment and posttreatment blood sample collections, given that half-lives of these compounds are thought to be 530 years (19 , 20) . Moreover, we found no association between the length of time between blood draws and the change in chemical levels. Furthermore, a study of healthy women found little variation in serum samples collected over a 3-month interval (21) , although this was shorter than the interval in our study.
In addition to the true biological elimination of the chemical, temporal changes in body weight may influence serum levels of PCBs and DDT because organochlorines are stored in adipose tissue. Our data show no association between weight change and decline in chemical levels.
The consistency of the decrease across all chemicals and the large magnitude of the decline suggest that chemotherapy may account for the change. With these data, it is not possible to determine whether values had already fallen, had risen, or stayed the same after diagnosis.
We were not able to look at intervening periods that precisely mimic the sample collection window of a population-based case-control study with rapid ascertainment (i.e., <1 month after diagnosis). It would be instructive to follow cases over the entire treatment course with samples collected frequently to clarify when the decline occurs. We are currently following a series of cases from pretreatment over the course of chemotherapy with the second and third blood draws occurring within a few months, thereby determining whether we see a change in organochlorine levels during the time frame that is relevant for a population-based case-control study with rapid ascertainment. Although we did not have a control group in our study, we felt that it was important to publish this initial evaluation from a sample of convenience because of its unexpected results and to raise a cautionary note for people attempting to study the organochlorine-NHL relationship in a case-control study.
One could speculate that lymphoma itself increases serum organochlorine levels, which then revert to predisease levels among patients who respond to treatment. If the disease causes weight loss, this could release stored organochlorines into the blood stream and organochlorine levels would therefore be elevated. We cannot exclude this scenario because many of our cases had low-grade lymphomas and either partial or complete response to treatment. Our data did not allow us to examine directly a possible disease effect. To indirectly assess such an effect, one could evaluate levels in a range of untreated cases with different stages/grades.
Our study has several strengths. We took advantage of previously collected serum samples from a well-documented NCI clinical trial with a patient population that was fairly homogeneous in stage/grade level and treatment regimen. Furthermore we were able to examine the effect of weight change.
Overall, if there is no evidence of a disease effect and decline does not occur during the first few months of treatment (or is so highly consistent across cases that it can be adjusted for in the analysis), case-control studies may have a role in studying the organochlorine-NHL hypothesis. If these issues cannot be clearly resolved, then the resolution of this hypothesis will require large cohort studies.
| Acknowledgments |
|---|
| Footnotes |
|---|
1 To whom requests for reprints should be
addressed, at Division of Cancer Epidemiology and Genetics, National
Cancer Institute, Executive Plaza South, Room 8122, Bethesda, MD
20892-7240. Phone: (301) 435-4707; Fax: (301) 402-1819; E-mail: barisd{at}epndce.nci.nih.gov ![]()
2 The abbreviations used are: NHL, non-Hodgkins
lymphoma; DDT,
2,2-bis-(p-chlorophenyl)-1,1,1-trichloroethane; DDE,
1,1-dichloro-2,2-bis(p-chloro-phenyl)ethylene; PCB,
polychlorinated biphenyl; NCI, National Cancer Institute. ![]()
Received 5/21/99; revised 11/15/99; accepted 11/24/99.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
T. T. Vo, B. C. Gladen, G. S. Cooper, D. D. Baird, J. L. Daniels, M. D. Gammon, and D. B. Richardson Dichlorodiphenyldichloroethane and Polychlorinated Biphenyls: Intraindividual Changes, Correlations, and Predictors in Healthy Women from the Southeastern United States Cancer Epidemiol. Biomarkers Prev., October 1, 2008; 17(10): 2729 - 2736. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. L. Biggs, M. D. Davis, D. L. Eaton, N. S. Weiss, D. B. Barr, D. R. Doody, S. Fish, L. L. Needham, C. Chen, and S. M. Schwartz Serum Organochlorine Pesticide Residues and Risk of Testicular Germ Cell Carcinoma: A Population-Based Case-Control Study Cancer Epidemiol. Biomarkers Prev., August 1, 2008; 17(8): 2012 - 2018. [Abstract] [Full Text] [PDF] |
||||
![]() |
P Cocco, P Brennan, A Ibba, S de Sanjose Llongueras, M Maynadie, A Nieters, N Becker, M G Ennas, M G Tocco, and P Boffetta Plasma polychlorobiphenyl and organochlorine pesticide level and risk of major lymphoma subtypes Occup. Environ. Med., February 1, 2008; 65(2): 132 - 140. [Abstract] [Full Text] [PDF] |
||||
![]() |
M. S. Wolff, H. A. Anderson, J. A. Britton, and N. Rothman Pharmacokinetic Variability and Modern Epidemiology The Example of Dichlorodiphenyltrichloroethane, Body Mass Index, and Birth Cohort Cancer Epidemiol. Biomarkers Prev., October 1, 2007; 16(10): 1925 - 1930. [Full Text] [PDF] |
||||
![]() |
L. S. Engel, F. Laden, A. Andersen, P. T. Strickland, A. Blair, L. L. Needham, D. B. Barr, M. S. Wolff, K. Helzlsouer, D. J. Hunter, et al. Polychlorinated Biphenyl Levels in Peripheral Blood and Non-Hodgkin's Lymphoma: A Report from Three Cohorts Cancer Res., June 1, 2007; 67(11): 5545 - 5552. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. J. De Roos, P. Hartge, J. H. Lubin, J. S. Colt, S. Davis, J. R. Cerhan, R. K. Severson, W. Cozen, D. G. Patterson Jr., L. L. Needham, et al. Persistent Organochlorine Chemicals in Plasma and Risk of Non-Hodgkin's Lymphoma Cancer Res., December 1, 2005; 65(23): 11214 - 11226. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. E. Muscat, J. A. Britton, M. V. Djordjevic, M. L. Citron, M. Kemeny, E. Busch-Devereaux, B. Pittman, and S. D. Stellman Adipose Concentrations of Organochlorine Compounds and Breast Cancer Recurrence in Long Island, New York Cancer Epidemiol. Biomarkers Prev., December 1, 2003; 12(12): 1474 - 1478. [Abstract] [Full Text] [PDF] |
||||
![]() |
K Teschke, A F Olshan, J L Daniels, A J De Roos, C G Parks, M Schulz, T L Vaughan, and H Kromhout Occupational exposure assessment in case-control studies: opportunities for improvement Occup. Environ. Med., September 1, 2002; 59(9): 575 - 594. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |