CORRELATION BETWEEN PLASMA TAMOXIFEN CONCENTRATION AND TUMOR RESPONSE IN PATIENTS WITH BREAST CANCER: AT NEOADJUVANT TREATMENT WITH TAMOXIFEN

Objective: to determine a possible correlation between the tumor response in patients suffering from breast cancer, initially treated with tamoxifen, and plasma concentration of this drug.Methods: we studied 27 elderly patients (age range: 62 to 82 y) with advanced breast carcinoma who were treated with a daily dose of 20 mg of oral tamoxifen, for 3 mo. Responders were followed-up for 19 mo, and nonresponders for 21 mo. We measured plasma tamoxifen citrate levels in order to determine their possible correlation with objective remission of the disease.Results: the correlation was found to be significant among responders (37%), whose median plasma tamoxifen level was 187.40ng. ml-1, when comparing to non-responders, whose median plasma tamoxifen level was 99.52ng. ml-1. The frequency distribution of patients in both groups with concentration of tamoxifen lower and higher than 182.60ng. ml-1 was significant (fisher's test p-value<0,0011).Conclusion: considering the results herein, we suggest that patients whose plasma tamoxifen levels reach 182.60ng. ml-1 after 3 mo of treatment, with no tumor response, may not benefit from this treatment, and an alternative therapy should be regarded