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Oral Contraceptives and Survival in Breast Cancer Patients Aged 20 to 54 Years

Departments of ¹ Epidemiology and ² Biostatistics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; ³ Cancer Prevention Program, ⁴ Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington; ⁵ Department of Epidemiology, Rollins School of Public Health, Emory University, ⁶ Surveillance and Epidemiology Branch, Divisions of Global Migration and Quarantine and ⁷ Cancer Prevention and Control, National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention, and ⁸ Winship Cancer Center, Emory University School of Medicine, Atlanta, Georgia; ⁹ Department of Community and Family Medicine, Cancer Prevention and Control Research Program, Duke University Medical Center, Durham, North Carolina; and ¹⁰ Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Department of Health and Human Services, Bethesda, Maryland

Requests for reprints: Katrina F. Trivers, Division of Cancer Prevention and Control, Centers for Disease Control and Prevention, 4770 Buford Highway, NE, MS K-52, Atlanta, GA 30341. Phone: 770-488-1086; Fax: 770-488-4760. E-mail: ktrivers{at}cdc.gov

	Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
Recent oral contraceptive (OC) use is associated with modestly higher breast cancer incidence among younger women, but its impact on survival is unclear. This study examined the relationship between OC use before breast cancer diagnosis and survival. A population-based sample of 1,264 women aged 20 to 54 years with a first primary invasive breast cancer during 1990 to 1992 were followed up for 8 to 10 years. OC and covariate data were obtained by interviews conducted shortly after diagnosis and from medial records. All-cause mortality was ascertained through the National Death Index (n = 292 deaths). Age- and income-adjusted hazard ratios (HR) and 95% confidence intervals (95% CI) were estimated by Cox regression methods. All-cause mortality was not associated with ever use of OCs or duration of use. Compared with nonusers, mortality estimates were elevated among women who were using OCs at diagnosis or stopped use in the previous year (HR, 1.57; 95% CI, 0.95-2.61). The HR for use of high-dose estrogen pills within 5 years before diagnosis was double that of nonusers (HR, 2.39; 95% CI, 1.29-4.41) or, if the most recent pill included the progestin levonorgestrel, compared with nonusers (HR, 2.01; 95% CI, 1.03-3.91). Because subgroup estimates were based on small numbers of OC users, these results should be cautiously interpreted. Overall, most aspects of OC use did not seem to influence survival, although there is limited evidence that OC use just before diagnosis, particularly use of some pill types, may negatively impact survival in breast cancer patients aged 20 to 54 years. (Cancer Epidemiol Biomarkers Prev 2007;16(9):1822–7)

	Introduction

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Use of oral contraceptive (OC) pills is common. In the 2002 National Survey of Family Growth, OCs were the leading method of contraception, with 82% of U.S. women aged 15 to 44 years reporting ever using them (1). Worldwide, more than 300 million women have ever used OCs (2). Thus, understanding the full range of health effects associated with their use is important.

Among younger women, current or recent OC use and use of higher dose and potency pills have been associated with modestly higher breast cancer incidence (3, 4), but effects on survival are unclear (5-22). To date, no studies have examined pill characteristics and survival.

The number of female breast cancer survivors was estimated to be 2.36 million in 2003 (23). Obesity at diagnosis has been associated with increased mortality, possibly due to estrogen-mediated mechanisms (24). Thus, other hormone-related characteristics (e.g., OC use) may influence survival, possibly contributing to the higher mortality among younger patients (23).

This large, population-based study of breast cancer patients aged 20 to 54 years with detailed data on OC use investigated associations between survival and OC use before diagnosis, including ever use, duration, age at first use and last use, duration of use before age 25, duration of use before a first birth, and time since first and last use. We also examined whether survival systematically differed according to OC dose, potency, or formulation.

	Materials and Methods

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Parent Case-Control Study and Current Study Population
A cohort of patients with invasive breast cancer previously enrolled in a population-based case-control study (25) was followed to investigate predictors of survival. The parent case-control study included 2,203 patients, aged 20 to 54 years, diagnosed with primary in situ or invasive breast cancer between May 1, 1990, and December 31, 1992, who were residents of central New Jersey, metropolitan Atlanta, GA, and metropolitan Seattle, WA (25). Structured in-person interviews were conducted by trained interviewers shortly after diagnosis (median, 4.2 months). Interviews were completed for 86% of eligible in situ and invasive cases (25). Reasons for patients not being interviewed included refusal (5.4% physician refusal and 6.4% patient refusal), death (0.4%), and illness (0.6%; ref. 25).

The cohort of women in this report includes only the invasive breast cancer cases from New Jersey and metropolitan Atlanta, GA. Of the 1,283 patients in the cohort, 19 patients with missing vital status were excluded; 1,264 (98.5%) patients were included in this analysis and had follow-up for 8 to 10 years. Institutional Review Boards at collaborating institutions approved this study.

Exposure Assessment
Interviews from the case-control study provided data on OC use before diagnosis and most of the covariate information. A reproductive history calendar was used to help women recall OC use by relating it to key life events. For each episode of OC use, participants were asked the starting and stopping dates and to name the pill used. Color photographs and listings of all marketed pills were used to aid brand recognition.

To analyze OC dose, potency, and formulation, those who could not recall dates of use or pill types (202 women, 22.5% of users) or used progestin-only pills (6 women, <1% of users) were excluded, similar to our previous analyses (4). Because classification of pill content was complicated for use of multiple pills at different times for varying durations, components of combination OCs used during various periods were analyzed (4). This classification included information on the pill used during (a) the most recent period, (b) the longest period within 5 years before diagnosis, (c) the longest period within 10 years before diagnosis, and (d) the longest period. For each period, the corresponding OC was classified by formulation (estrogen and progestin type), potency (cross-classification of estrogen and progestin potency), and estrogen dose. Potency was calculated as previously described (4), according to the scheme of Piper and Kennedy (26), which classifies OCs by pharmacologic effects on target organs. Pills with progestins of intermediate potency were ultimately classified as low progestin potency. Pills with estrogens of intermediate potency were defined as low estrogen potency if they contained 35 µg ethinyl estradiol or 50 µg mestranol; otherwise, they were defined as high potency.

Summary disease stage (local, regional, or distant; ref. 27), tumor grade, and estrogen and progesterone receptor status were abstracted from medical records in the case-control study. In the interview, all patients were queried about previous treatment. In Atlanta only, more detailed information on disease stage according to the American Joint Committee on Cancer (28) and the first course of breast cancer treatment (radiation, chemotherapy, hormonal therapy, and surgery) were available from the Surveillance, Epidemiology, and End Results program and additional medical record review.

Outcome Ascertainment
Follow-up time was calculated from diagnosis to death or study completion (median, 8.5 years; range, 3 months to 9.8 years). Linkage to the National Death Index provided data on vital status and date and cause of death. By the end of follow-up (January 1, 2000), there were 292 deaths; 248 (85%) attributed to breast cancer, 15 (5%) to cardiovascular disease, 13 (4.5%) to other causes (infections, accidents, other cancers, diabetes, and liver disease), and 16 (5.5%) had no cause of death listed.

Statistical Analyses
The proportional hazards assumption was assessed through log(–log(survival)) plots and including interactions with follow-up time. Household income and time since last OC use violated this assumption. Time-dependent covariates were introduced to address the violation. The nonproportionality for income was addressed by including an interaction term between income and follow-up time. For time since last OC use, the log(–log(survival)) plot revealed that there was a cross-over at 24 months (i.e., the effect of time since last OC use was different before and after 24 months of follow-up). Therefore, we added an interaction term between time since last OC use and an indicator function for follow-up time being >24 months, which allowed for the effect of time since last use to differ before and after 24 months of follow-up. Variables were categorized based on exploratory analyses of the data and were modeled by indicator variables.

Adjusted hazard ratios (HR) and 95% confidence intervals (95% CI) were estimated by Cox regression methods (29). Because the quality of cause of death information on death certificates has been questioned in at least one study (30), all-cause mortality was the main end point, and patients alive at the end of follow-up were censored. Analyses of breast cancer–specific mortality were also conducted, and participants who died of causes other than breast cancer were censored. Modeling was done separately for each attribute of OC use: ever use for 6 months, duration, age at first use, age at last use, duration of use before age 25, duration of use before a first birth, time since first use, and time since last use. To be consistent with previous analyses based on the same group of breast cancer patients (4, 25), the reference group for all analyses reported here is non-OC users, defined as those who used OCs for less than 6 months (including never users). Results were similar when never users were used as the reference (data not shown).

Covariates were initially included in multivariable models if they were associated both with the particular OC variable and mortality in bivariate analyses. Potential confounders included age at diagnosis, education, household income, physical activity (at age 20 and the year before diagnosis), body mass index (at age 20 and the year before diagnosis), family history of breast cancer, race, smoking status, alcohol consumption, parity, age at menarche, recency of giving birth, study site, comorbidity (thyroid disease, diabetes, high cholesterol, high blood pressure, and cancers other than breast cancer), method of cancer detection (e.g., accidental, routine self-examination, or mammogram), chemotherapy or radiation before interview, summary stage, tumor grade, and hormone receptor status. Model building proceeded through backward elimination, and variables were retained if inclusion caused >10% change in the estimate for the OC characteristic. All results were adjusted for age (<35, 35-44, or 45-54 years) and annual household income (<$15,000, $15,000 to <$25,000, $25,000 to <$90,000, or $90,000) because these were the only consistent confounders. Each OC use and mortality estimate was also adjusted for additional confounders specific to that association (listed in the footnotes to Tables 2–4). Estimates adjusted for summary stage, tumor grade, and hormone receptor status were similar to estimates without adjustment. In the Atlanta subgroup, adjustment for the detailed treatment information or stage according to the American Joint Committee on Cancer did not alter any estimates.

	Results

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The majority of women were 35 to 44 years of age, had local disease, and were premenopausal (Table 1 ). Of the 1,264 participants, 367 (29.0%) were non-OC users, 122 (9.7%) started use at or before 18 years of age, and 97 (7.7%) were using OCs or had recently stopped use at diagnosis of breast cancer (data not shown).

Timing of OC use before breast cancer diagnosis seemed to affect survival, although estimates were not statistically significant (Table 2). Users at diagnosis or those who had stopped OC use in the previous year tended to have higher all-cause mortality versus nonusers (HR, 1.57; 95% CI, 0.95-2.61), but only after 24 months of follow-up (Table 2). A similar point estimate (HR, 1.60) was observed for having recently started OCs (<10 years before diagnosis). When we included both time since first use and time since last use in the same model, the estimates for each were unchanged.

Women who used high-dose estrogen pills (>35 µg of ethinyl estradiol or >50 µg of mestranol) in the 5 years before diagnosis were more than twice as likely to die than nonusers (HR, 2.39; 95% CI, 1.29-4.41; Table 3 ). Pill potency was not independently associated with mortality. Across all examined periods, use of the progestin levonorgestrel was associated with higher mortality. For example, the HR for use of levonorgestrel in the most recently used pill was 2.01 (95% CI, 1.03-3.91), relative to nonusers. However, use of levonorgestrel in multiple periods was highly correlated, so it was difficult to determine which period was most important. After examining all progestins separately (data not shown), levonorgestrel was the only progestin that seemed to affect survival; therefore, all other progestins were grouped together. Adjustment for dose and potency did not alter time since first and last use estimates.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Results of previous studies on OCs and mortality among women with breast cancer have been inconsistent; a few reported lower mortality among OC users (6, 17), and some reported higher mortality (12, 13, 15, 16, 20, 21) or no effect (5, 7-11, 14, 18, 19, 22). Our null results for duration of use are consistent with most previous work (9, 14, 16, 18). Two studies observed that although recent OC users had a similar risk of death compared with never users, mortality decreased with increasing time since last OC use (therefore, recent OC users had increased mortality relative to non–recent users; refs. 16, 21). For example, the HR for more than 10 years since last OC use relative to nonusers was 0.85 (95% CI, 0.61-1.18), with a significant trend among users (21). Other studies have not observed associations between recent OC use and mortality (9, 14, 17, 18). Previous research was limited by the use of non-population–based samples and broad classification of exposure to OCs (6, 8, 10, 11, 13, 19). The earliest studies were limited by small sample sizes of women exposed to OCs (5, 6, 8, 11, 13).

In this study, time since first and last use was associated with mortality, although confidence intervals were wide; however, duration was not associated with mortality. This is similar to the results observed in the parent study for recency of use and risk of developing breast cancer (25). Despite the modest correlation between time since first and last use and total duration, duration and timing may represent two aspects of use. Whereas long duration of use can span different periods relative to a breast cancer diagnosis, it seems that only OC use close to diagnosis affects survival. A lack of observed trend in our results may result from small numbers of recent OC users, particularly in the 1- to 4-year range. Our results for time since first and last use do not seem to be explained by unusual patient characteristics. Recent OC users were more likely to be younger, be nulliparous or have fewer children, and were more likely to have had a recent birth and to have tumors that were discovered by self-examination rather than mammography (data not shown). Adjustment for parity, time since last birth, or mammography did not alter estimates for time since first and last OC use.

Higher mortality was associated with the progestin levonorgestrel and high-dose estrogen formulations. These results are noteworthy but should be interpreted cautiously because a small proportion of women used these formulations. Furthermore, pill types are not prescribed randomly, and no data were available on the reasons women used certain pill formulations. However, our results for high-dose estrogen pills mirror results observed in the parent case-control study for incidence (4). Mortality was higher among recent OC users, regardless of dose and formulation. For OCs taken in less recent periods (>5 to 10 years before diagnosis), content was not related to mortality, suggesting that only pills used recently in relation to diagnosis may affect mortality. Therefore, time since first and last use and pill content seem to be independent constructs of use. High-dose estrogen pills are not regularly dispensed currently, but many recently available pills contain levonorgestrel (31). Of OCs available in 2004, 21% contained levonorgestrel (32) versus 9% of pills used by women in this study. Levonorgestrel has higher potency and exhibits the highest level of androgenic activity relative to other progestins currently on the market (33).

Limitations include possible residual confounding by lifestyle changes after diagnosis. Although we did not collect postdiagnostic exposure and lifestyle data, OCs are contraindicated for women diagnosed with breast cancer (33). However, factors like income and obesity may have changed after diagnosis, but it remains uncertain whether postdiagnosis changes influence survival (34, 35).

Accurate recall of OC use in observational studies may also be problematic, but previous studies showed that recall is high when detailed questionnaires, reproductive calendars, and pill photographs are used (36, 37). Recall of specific brands is typically less accurate (36, 37), and in this study, 22.5% of OC users could not recall pill brand. Compared with participants who had complete content data, those with incomplete content data tended to be older (26% of those with complete data were 45 years versus 41% of those with incomplete data) and non–recent OC users (13.5% of those with complete data used OCs <1 year before diagnosis versus 1.5% of those with incomplete data). However, because women missing content data had similar mortality and income levels, bias was likely minimal, especially for recent pill use. Any bias was most likely nondifferential because completeness of the National Death Index is well validated (38). The accuracy of cause of death on death certificates remains equivocal (30, 39). We reached similar conclusions when using all-cause mortality (the primary end point of interest) or breast cancer–specific mortality.

Our results may not be generalizable to all breast cancer patients. Nonparticipation in the parent case-control study was often due to patient refusal or illness (25), so subsequent mortality was likely higher among nonresponders than among responders. Participation in the parent study was satisfactory (86%), although 83% of responders were ever OC users versus 76% of nonresponders (40). No data are available on the proportion of nonresponders who were recent users. It is unknown how inclusion of all potential participants in the study would have influenced the effect estimates. We had no follow-up information on the Seattle patients who participated in the original study. However, the parent study observed minimal differences in the OC results when stratifying by study site (25). In this present analysis, adjustment for study site did not affect the results. Therefore, it seems unlikely that the exclusion of the Seattle cases has materially biased the present results, although this cannot be completely ruled out.

Study strengths include use of data from a population-based study of young (<55 years of age) breast cancer patients with long-term follow-up and a comprehensive assessment of OC use. The focus on young women, many of reproductive age, is important because this population had ample opportunity for exposure to OCs. Due to comparatively recent diagnosis of breast cancer, exposure to OCs in this study population is more similar to that for current breast cancer survivors than in previous cohorts. To our knowledge, there is no published literature on pill attributes such as dose and potency in relation to breast cancer survival. The detailed nature of the OC data in this study allowed examination of these relationships.

Many women take OCs, often for years. Therefore, a greater understanding of their specific health effects is important. Mortality among OC users is lower than mortality associated with childbirth until age 40 for nonsmokers (33). Thus, comprehensive clinical recommendations about OC use at various ages would depend on a complex risk-benefit ratio.

In this population-based study of young breast cancer patients, most aspects of OC use were not associated with survival. However, there were provocative, but limited, indications that recent OC use may be associated with modest increased risk of mortality. The 2-fold increase in mortality associated with recent use of high-dose pills or levonorgestrel raises concern and deserves further investigation.

	Footnotes

 
Grant support: Susan G. Komen Breast Cancer Foundation (DISS0402898); the National Institute of Environmental Health Sciences, NIH (P30ES10126); Cancer Epidemiology Training Grant, University of North Carolina (T32 CA09330), and the Lineberger Cancer Control Education Program, University of North Carolina (R25 CA57726).

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Note: This manuscript represents original work and has not been previously published in this form. This work was presented in part at the American Association for Cancer Research Special Conference entitled New Developments in the Epidemiology of Cancer Prognosis: Traditional and Molecular Predictors of Treatment Response and Survival, January 11–15, 2006, Charleston, SC.

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

Received 1/17/07; revised 5/ 7/07; accepted 7/ 2/07.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

1. Mosher WD, Martinez GM, Chandra A, Abma JC, Willson SJ. Use of contraception and use of family planning services in the United States: 1982–2002. Advance data from vital and health statistics; No 350. Hyattsville (MD): National Center for Health Statistics; 2004.
2. Cogliano V, Grosse Y, Baan R, Straif K, Secretan B, El Ghissassi F. Carcinogenicity of combined oestrogen-progestagen contraceptives and menopausal treatment. Lancet Oncol 2005;6:552–3.[CrossRef][Medline]
3. Collaborative Group on Hormonal Factors in Breast Cancer. Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53 297 women with breast cancer and 100 239 women without breast cancer from 54 epidemiological studies. Lancet 1996;347:1713–27.[CrossRef][Medline]
4. Althuis MD, Brogan DR, Coates RJ, et al. Hormonal content and potency of oral contraceptives and breast cancer risk among young women. Br J Cancer 2003;88:50–7.[CrossRef][Medline]
5. Spencer JD, Millis RR, Hayward JL. Contraceptive steroids and breast cancer. Br Med J 1978;1:1024–6.[Abstract/Free Full Text]
6. Matthews PN, Millis RR, Hayward JL. Breast cancer in women who have taken contraceptive steroids. Br Med J (Clin Res Ed) 1981;282:774–6.[Medline]
7. Vessey M, Baron J, Doll R, McPherson K, Yeates D. Oral contraceptives and breast cancer: final report of an epidemiological study. Br J Cancer 1983;47:455–62.[Medline]
8. Greenberg ER, Vessey MP, McPherson K, Doll R, Yeates D. Body size and survival in premenopausal breast cancer. Br J Cancer 1985;51:691–7.[Medline]
9. Rosner D, Lane WW. Oral contraceptive use has no adverse effect on the prognosis of breast cancer. Cancer 1986;57:591–6.[CrossRef][Medline]
10. Millard FC, Bliss JM, Chilvers CE, Gazet JC. Oral contraceptives and survival in breast cancer. Br J Cancer 1987;56:377–8.[Medline]
11. Mohle-Boetani JC, Grosser S, Whittemore AS, Malec M, Kampert JB, Paffenbarger RS, Jr. Body size, reproductive factors, and breast cancer survival. Prev Med 1988;17:634–42.[CrossRef][Medline]
12. Olsson H, Moller T, Ranstam J, Borg A, Ferno M. Early oral contraceptive use as a prognostic factor in breast cancer. Anticancer Res 1988;8:29–32.[Medline]
13. Lees AW, Jenkins HJ, May CL, Cherian G, Lam EW, Hanson J. Risk factors and 10-year breast cancer survival in northern Alberta. Breast Cancer Res Treat 1989;13:143–51.[CrossRef][Medline]
14. Ewertz M, Gillanders S, Meyer L, Zedeler K. Survival of breast cancer patients in relation to factors which affect the risk of developing breast cancer. Int J Cancer 1991;49:526–30.[Medline]
15. Ranstam J, Olsson H, Garne JP, Aspegren K, Janzon L. Survival in breast cancer and age at start of oral contraceptive usage. Anticancer Res 1991;11:2043–6.[Medline]
16. Holmberg L, Lund E, Bergstrom R, Adami HO, Meirik O. Oral contraceptive and prognosis in breast cancer: effects of duration, latency, recency, age at first use and relation to parity and body mass index in young women with breast cancer. Eur J Cancer 1994;30A:351–4.[CrossRef]
17. Schonborn I, Nischan P, Ebeling K. Oral contraceptive use and the prognosis of breast cancer. Breast Cancer Res Treat 1994;30:283–92.[CrossRef][Medline]
18. Schouten LJ, Hupperets PS, Jager JJ, et al. Prognostic significance of etiological risk factors in early breast cancer. Breast Cancer Res Treat 1997;43:217–23.[CrossRef][Medline]
19. Sauerbrei W, Blettner M, Schmoor C, Bojar H, Schumacher M. The effect of oral contraceptive use on the prognosis of node positive breast cancer patients. Eur J Cancer 1998;34:1348–51.[Medline]
20. Saxe GA, Rock CL, Wicha MS, Schottenfeld D. Diet and risk for breast cancer recurrence and survival. Breast Cancer Res Treat 1999;53:241–53.[CrossRef][Medline]
21. Reeves GK, Patterson J, Vessey MP, Yeates D, Jones L. Hormonal and other factors in relation to survival among breast cancer patients. Int J Cancer 2000;89:293–9.[CrossRef][Medline]
22. Gonzalez-Angulo AM, Broglio K, Kau SW, et al. Women age < or = 35 years with primary breast carcinoma: disease features at presentation. Cancer 2005;103:2466–72.[CrossRef][Medline]
23. Ries LAG, Harkins D, Krapcho M, et al. editors. SEER Cancer Statistics Review, 1975–2003, National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/csr/1975_2003/, based on November 2005 SEER data submission, posted to the SEER web site, 2006.
24. Whiteman MK, Hillis SD, Curtis KM, McDonald JA, Wingo PA, Marchbanks PA. Body mass and mortality after breast cancer diagnosis. Cancer Epidemiol Biomarkers Prev 2005;14:2009–14.[Abstract/Free Full Text]
25. Brinton LA, Daling JR, Liff JM, et al. Oral contraceptives and breast cancer risk among younger women. J Natl Cancer Inst 1995;87:827–35.[Abstract/Free Full Text]
26. Piper JM, Kennedy DL. Oral contraceptives in the United States: trends in content and potency. Int J Epidemiol 1987;16:215–21.[Abstract/Free Full Text]
27. Shambaugh EM, Weiss MA, Axtell LM, editors. Summary Staging Guide for the Cancer Surveillance, Epidemiology, and End Results Reporting (SEER) Program, 1977.
28. Fleming ID, Cooper JS, Henson DE, editors. American Joint Committee on Cancer Staging manual. Philadelphia: Lippincott-Raven; 1997.
29. Cox D. Regression models and life tables. J R Stat Soc 1972;34:187–220.
30. Sington JD, Cottrell BJ. Analysis of the sensitivity of death certificates in 440 hospital deaths: a comparison with necropsy findings. J Clin Pathol 2002;55:499–502.[Abstract/Free Full Text]
31. Hatcher R, Trussell J, Stewart F, et al. Contraceptive technology. New York: Ardent Media, Inc.; 2004.
32. Drug facts and comparisons, 2004 edition. St. Louis: Wolters Kluwer Health.
33. Drug facts and comparisons, 2006 edition. St. Louis: Wolters Kluwer Health.
34. Kroenke CH, Chen WY, Rosner B, Holmes MD. Weight, weight gain, and survival after breast cancer diagnosis. J Clin Oncol 2005;23:1370–8.[Abstract/Free Full Text]
35. Chirikos TN, Russell-Jacobs A, Cantor AB. Indirect economic effects of long-term breast cancer survival. Cancer Pract 2002;10:248–55.[CrossRef][Medline]
36. Coulter A, Vessey M, McPherson K, Crossley B. The ability of women to recall their oral contraceptive histories. Contraception 1986;33:127–37.[CrossRef][Medline]
37. Norell SE, Boethius G, Persson I. Oral contraceptive use: interview data versus pharmacy records. Int J Epidemiol 1998;27:1033–7.[Abstract/Free Full Text]
38. Rich-Edwards J, Corsano K, Stampfer M. Test of the National Death Index and Equifax national search. Am J Epidemiol 1994;140:1016–9.[Abstract/Free Full Text]
39. Lash TL, Silliman RA, Guadagnoli E, Mor V. The effect of less than definitive care on breast carcinoma recurrence and mortality. Cancer 2000;89:1739–47.[CrossRef][Medline]
40. Madigan MP, Troisi R, Potischman N, et al. Characteristics of respondents and non-respondents from a case-control study of breast cancer in younger women. Int J Epidemiol 2000;29:793–8.[Abstract/Free Full Text]

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