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No association found between CYP2D6 use during tamoxifen therapy and breast cancer recurrence
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Dutch researchers conducting an observational study of women treated with tamoxifen for breast cancer have concluded that the concomitant use of a CYP2D6 was not associated with disease recurrence.
Researchers reviewed data on 1,962 women with breast cancer collected in three databases, including the Dutch Medical Register, from 1994 to 2006.
There were 213 patients co-prescribed a CYP2D6 inhibitor, and of those, 150 patients (7.6%) were assigned a CYP2D6 inhibitor for at least 60 days.
During the 7,631 person-years reviewed there were 283 breast cancers. A total of 265 cancers were diagnosed in 7,183 person-years without inhibitor use, whereas 18 cancers were diagnosed in 447.6 person-years after the definition of concomitant CYP2D6 inhibitor use was met.
Researchers found no difference in event-free time between patients assigned a CYP2D6 inhibitor and those who were not (HR=0.87; 95% CI, 0.42-1.79). Similarly, they found no interaction between adherence to tamoxifen and any or strong CYP2D6 inhibitor use. Results did not change when other definitions for CYP2D6 inhibitor use were applied.
Poor adherence to the tamoxifen regimen was associated with worse event-free time (HR= 0.987; 95% CI, 0.975-0.999). When researchers categorized adherence, patients with at least 80% adherence had a 26% reduced risk for breast cancer and those with at least 90% adherence saw their risk decline by 27%.
Dezentjè VO. J Clin Oncol. 2010;doi:10.1200/JCO.2009.25.0894.
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