Age/Body Mass Index Affect Tam Metabolism

DOD-BCR: Age and body mass index affect tamoxifen metabolism and should be considered when prescribing tamoxifen therapy for breast cancer

By Peggy Peck Special to DG News

ORLANDO, FL -- October 1, 2002 -- Both age and body mass index (BMI) influence serum levels of tamoxifen metabolites and thus should be considered when prescribing tamoxifen, according to a study presented at the Department of Defense Breast Cancer Research Program conference.

Jodi Flaws, PhD, and colleagues from the University of Maryland School of Medicine, Baltimore, Maryland and the Bioanalytical Science Group, University of London based their conclusion on a study of 87 breast cancer patients who had been taking tamoxifen for at least 30 days.

Thirty nine women were African American and 48 were Caucasian. The women were asked to complete a questionnaire that included questions relating to race, current BMI and current age. Blood samples were used to measure each woman's serum level of tamoxifen, as well tamoxifen metabolites N-desmethyltamoxifen (N-DMT) and 4-hydroxytamoxifen (4-OHT). Samples were analyzed by quantitative high-performance liquid chromatography/mass spectrometry.

Dr. Flaws said results indicated that levels of tamoxifen, N-DMT and 4-OHT differed considerably even though the women were each receiving 20 mg/d of tamoxifen.The tamoxifen levels ranged from 1-124 ng/ml, N-DMT levels ranged from 1-150 ng/ml and 4-OHT levels from 1-11 ng/ml.

The results indicated that BMI was significantly associated with 4-OHT levels. A woman with a BMI of less than 30 kg/m2 had 5.5 0.8 ng/ml while women with a BMI of 30 kg/m2 or more had 4-OHT levels of just 2.8 1.1 ng/ml, which was significant at a p of 0.05 or less.

In a similar fashion, age was associated with N-DMT levels. Women older than 58 had 69.3 8.4 ng/ml of N-DMT while younger women had N-DMT levels in the range of 46.27.7 ng/ml. This was also significant at a p of 0.05 or less, she said. The associations remained after adjusting for confounders.

Dr. Flaws suggests that prescribing the same dose of tamoxifen to all women may not be accurate based on these results.

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