Anticoagulants, radiation, and prostate cancer outcomes

Data presented last Monday at the annual meeting of the American Society for Radiation Oncology (ASTRO) suggest a possible role of anticoagulant therapy (using drugs like aspirin, warfarin, or clopidogrel/Plavix) in combination with radiation for the treatment of localized prostate cancer.

Choe and colleagues conducted a retrospective analysis of data from 662 men with localized prostate cancer treated with seed implants and/or external-beam radiation at the University of Chicago between 1988 and 2005. Of these men, 243 (36.7 percent) were receiving warfarin, clopidogrel, and/or aspirin. Most of the men were receiving aspirin alone (n = 161) or warfarin alone (n = 42). About half the men also received short-term androgen deprivation therapy (ADT).

Among the 243 patients, risk was low in 38 percent, intermediate in 38 percent, and high in 25 percent, according to National Comprehensive Cancer Network criteria.

In a subgroup analysis, among low- and intermediate-risk men taking anticoagulants, the improvement in biochemical control was apparent (but not statistically significant) compared with the respective risk groups of men not taking the drugs. However, in the high-risk patients (n = 165), the improvement in biochemical control was statistically significant. In that subgroup, the men taking anticoagulants (n = 52) had a 4-year rate of freedom from biochemical recurrence of 82.4 percent, compared with 57.6 percent for those not taking anticoagulants (n = 113). The type of radiation received did appear to influence biochemical outcomes.

In addition, anticoagulant therapy had second benefit. The risk for distant metastasis at 4 years after treatment was significantly lower in the patients taking anticoagulants than in those not taking anticoagulants (1 vs. 5 percent). “Anticoagulants may inhibit a tumor’s ability to spread,” said Dr. Choe, adding that “mounting preclinical evidence” supports this hypothesis.

In comments in a Medscape report on this paper, Leo R. Zacharski, MD, from the White River Junction VA Medical Center in Vermont and the Dartmouth School of Medicine in Hanover, New Hampshire — who is an expert on anticoagulants and cancer therapy — appeared to be utterly unsurprised by these findings, indicating that there is already a “very large” body of scientific literature on this topic.

It should be noted, however, that anticoagulant therapy also affects the risk of rectal bleeding in men receiving radiation therapy for prostate cancer. Therefore, the potential benefits need to be carefully assessed against the potential risks before there is any specific recommendation to add anticoagulation therapy to radiation therapy for even men with localized, high-risk prostate cancer.

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