In a univariate Cox regression analysis, the researchers found no difference in event-free time between women who did not use CYP2D6 inhibitors and women who used concomitant tamoxifen and CYP2D6 inhibitors (HR, 0.95; P = .73). “Even if we restricted our analysis to strong inhibitors, we could not find any difference,” Dr. Dezentjé said. Dr. Dezentjé and his coauthors reported that they have no relevant financial relationships.
Dr. Stearns noted that both of the studies have several limitations. Both were retrospective studies with relatively small sample sizes and limited follow-up. “In addition, there may be incomplete accountability for recurrences, as those were determined by hospital admission. As we know, breast cancer is very much an outpatient disease.” Moreover, the reason for inhibitor use is not known in either study.
In the Medco cohort, claims data are limited, and women with early recurrences or with low medication possession rates were excluded. In the European cohort, “the magnitude of the effect may have been diluted by short concomitant medication use,” she said.
Dr. Stearns reported that she had significant financial relationships with several pharmaceutical companies.
Even concomitant use of drugs deemed to be strong inhibitors didn't increase breast cancer recurrence. DR. DEZENTJÉ