By Dr Sharan Sharma

Tamoxifen use in breast cancer is associated with increase in thromboembolic events (TEs). Factor V Lieden (FVL) mutation, the most common clotting factor mutation, is an important risk factor for thrombolic events. But does taking tamoxifen with FVL mutation mean women are at an increased risk of TEs than those taking tamoxifen without FVL mutation?

According to the study published in the Journal of National Cancer Institute (JNCI) June 16th issue, there is an increased risk of a FVL mutation among women taking adjuvant tamoxifen for early-stage breast cancer who experienced a TE compared with those who did not.

To come to these conclusion researchers from the USA conducted a case-control study among 34 cancer and leukemia group B institutions. They matched each of 124 women who had experienced a documented TE while taking adjuvant tamoxifen for breast cancer to two control subjects (women who took adjuvant tamoxifen but did not experience TE) by age at diagnosis and they took DNA from those samples for FVL mutation. The statistical analysis revealed that FVL mutations were present in 23 (18.5%) case and 12 (4.8%) control subjects (Odds Ratio (OR) = 4.66, 95% confidence interval = 2.14 to 10.14, P < .001). In the multivariable logistic regression model, the likelihood of having had a TE while taking adjuvant tamoxifen was statistically significantly increased among women who carried the FVL mutation (OR = 4.73, 95% CI = 2.10 to 10.68, P < .001).

The researchers said "Our study clearly shows that women who experience TE events after taking tamoxifen have a 4.66-fold chance of carrying the FVL mutation".

"These data may prove useful to women who must decide between tamoxifen and an effective, essentially nonthrombogenic, alternative adjuvant therapy for breast cancer, such as aromatase inhibitors for postmenopausal women and gonadotropin-releasing hormone analogs or oophorectomy for premenopausal women" they added.