Safety of a novel capecitabine dosing schedule when combined with lapatinib in patients with HER2-positive metastatic breast cancer refractory to trastuzumab

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1131 Background: Capecitabine (C) is active in breast cancer and is usually dosed for 14 days (d) followed by a 7d rest (14 - 7). We described a mathematical method which predicts the optimal schedule for C to be 7d followed by a 7d rest (7 - 7) (Norton et al, Amer Assn Can Res. 2005). The MTD of C(7 - 7) is 2,000mg BID (Traina et al, J Clin Oncol. April 2008). Lapatinib (L) improves time to progression when added to C(14 - 7) in patients (pts) with HER-2-positive (+) metastatic breast cancer (MBC) that progressed after trastuzumab (T). To optimize this effective combination, we are testing C(7 - 7) + L in a phase II trial. Methods: Eligible pts have measurable, HER-2(+) MBC that has progressed after T. HER-2(+)=IHC 3+ or FISH>2. Pts have normal LVEF by MUGA, ECOG performance status (PS) <2 and normal organ function. <3 prior chemotherapy (CRx) regimens are permitted. Prior fluoropyrimidine is excluded. Therapy (tx) consists of C (2,000 mg BID, 7 - 7) and L (1,250 mg, daily). Cycle length = 4 wk. Pts are evaluated for toxicity q4 weeks (wk), for response q12wk; LVEF by MUGA q12wk. Primary endpoint: response rate (RR). Secondary endpoints: toxicity, stable disease >6 months, PFS. Using a Simon optimal 2-stage design, with alpha = 10%, power = 90% to discriminate between RR 10% and 25%, 21 pts will be accrued to the first stage. If >2 pts respond, 29 additional pts will be enrolled. If >7/ 40 pts respond, then C(7 - 7) + L will be considered worthy of further study. Results: As of January 5, 2008, 6 pts are enrolled and evaluable. Median (med) age 64 yrs (42–71), med ECOG PS 1 (0–1), ER/PR(+) 3, HER-2(+) 6, sites of MBC: bone (2), viscera (4), soft tissue (5). Med baseline LVEF 62% (51–68%). Prior tx: Adjuvant: CRx (5), hormone tx (3), T (3); MBC: CRx (2), hormone tx (1), T (3). After a med of 3 cycles (1–4), there were no grade 3, 4, or 5 events. Tx-related toxicity is: Gr 2 fatigue (1); Gr 1 AST (4), diarrhea (3), ALT (2), vomiting (1), hand-foot (1), fatigue (1). No withdrawls due to reduced LVEF. Two pts evaluable for response: PR = 1, SD<6 mo = 1. Conclusions: Capecitabine (7 - 7) + lapatinib appears well tolerated compared to C(14 - 7)+L (Geyer et al). Additional safety and efficacy data is anticipated prior to this meeting. [Table: see text]