Journal of Clinical Oncology, 2005 ASCO Annual Meeting Proceedings.
Vol 23, No 16S (June 1 Supplement), 2005: 508
© 2005 American Society of Clinical Oncology

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Abstract

Factor V Leiden (FVL) mutations and thromboembolic events (TE) in women with breast cancer on adjuvant tamoxifen

Dana-Farber Cancer Inst, Boston, MA; Duke Univ, Durham, NC; Roswell Park, Buffalo, NY; Univ of North Carolina, Chapel Hill, NC; Ohio State Univ, Columbus, OH; Yale Medcl Sch, New Haven, CT

508

Background: Tamoxifen (T) therapy has been associated with an increased risk of TE in women with breast cancer (BR) and in healthy women. In NSABP P-1, relative risk (RR) of DVT among women on T v. placebo was 1.60 (95% CI=0.91–2.86) and of PE was 3.01 (95% CI=1.15–9.27). FVL is a mutation in clotting Factor V that has been associated with increased TE risk with oral contraceptives and pregnancy. FVL was not associated with an increased risk of TE on T in high-risk women in NSABP P-1 or IBIS-1, but those analyses had small numbers of TE. Methods: A case-control study was conducted among CALGB institutions. Assuming a 1:2 case-control ratio, a total of 120 case-control sets were needed to provide 80% power to detect a RR=4 assuming a one-sided type I error rate= 0.05. Cases were 120 women who had had a documented DVT or PE while on adjuvant T, not necessarily on CALGB treatment trials. Controls were women with breast cancer who were taking or had taken adjuvant T with no TE, matched to the case on age at diagnosis (± 5 years). Data were collected on cancer stage, date of diagnosis, adjuvant chemotherapy use, smoking history and family TE history. Data on BMI and surgery (associated with TE on T in P-1 and IBIS, respectively) were not collected. Samples were analyzed for FVL mutations using multiplex PCR-based techniques. Conditional logistic regression was used to estimate the RR and 95% confidence interval. Results: This analysis is limited to 109 case-control triplets on whom complete data are available. Overall, 17 (15.6%) FVL mutations were seen in the cases; 10 (5%) in controls. The OR was 3.92 (95% CI=1.67 - 9.14, p<0.0001). Additional analysis will be provided. Conclusions: This is the largest case-control study designed to address the association between FVL and T-associated TE. The results from this study suggest that women with TE on T are almost 4 times more likely to have FVL than those without TE. Supported by Susan G. Komen Foundation.

No significant financial relationships to disclose.

Abstract presentation from the 2005 ASCO Annual Meeting