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Is Paclitaxel Less Cardiotoxic in the Treatment of Breast Cancer Before or After Doxorubicin?

Background: The combination of doxorubicin (DOX) with paclitaxel (PTX) effectively treats breast cancer (BC). However,DOX-associated cardiotoxicity (CTX) is aggravated by the use of PTX. Consensus is lacking about which drug sequence involves the most CTX. Objectives: To evaluate whether DOX followed by PXT or the reverse sequence has the greatest cardiotoxic potential in the treatment of BC. Methods: Prospective study of women with primary BC who received four cycles of DOX and 12 infusions of PTX. Participants were divided into Group 1 (G1; PXT before DOX) and Group 2 (G2; DOX before PXT) at the discretion of the oncologist. CTX was defined as an absolute reduction in left ventricular ejection fraction (LVEF) > 10% to a value <53%. Patients underwent clinical evaluations and echocardiography before treatment (Phase 1) and one year after treatment (Phase 2). Results: Sixty-nine women were evaluated: 19 in G1 and 50 in G2. The groups had similar clinical characteristics. The doses of radiation, DOX, and PTX used were similar. Eight (11.6%) patients developed CTX: two (10.5%) in G1 and six (12.0%) in G2 (p=0.62). The mean LVEF was similar between groups in Phase 1 (G1=65.1±3.5%; G2=65.2±3.9%; p=0.96), with a significant reduction noted after one year in both groups: G1=61.4±8.1% (p=0.021) and G2=60.8±7.6% (p<0.001). Although lower, mean LVEF remained similar between groups after Phase 2 (p=0.79). Conclusions: In women with BC who underwent chemotherapy, the incidence of CTX at the end of the first year of treatment was similar regardless of whether DOX was used before or after PTX.