E7389, a novel anti-tubulin, in patients with refractory breast cancer
653 Background: E7389 is a synthetic analog of halichondrin B, with a broad anti- proliferative activity against tumor cells. Methods: E7389 was evaluated in an open-label, single-arm Phase II trial as monotherapy for patients with refractory breast cancer (≥2 prior chemotherapy regimens, which must have included an anthracycline and a taxane). E7389 was administered as an IV bolus of 1.4 mg/m2 on Days 1, 8, and 15 of a 28-day cycle (group 1), or on Days 1 and 8 of a 21-day cycle (group 2). The primary efficacy endpoint was ORR. Results: As of 9 December 2005, 88 patients had received treatment, 68 in group 1 and 20 in group 2. Median age was 55 yrs (range 36–84) and ECOG performance status 0–1. Sixty-six percent of the tumors were ductal carcinomas, 6% lobular, and 27% were unclassified. Sixty percent of the tumors were ER+, 47% PR+, and 17% Her2/neu 3+. The patients had received at least two previous regimens, with a median number of 5 (range 2–14). Forty-eight percent of the patients had also used hormonal therapy. Forty-nine patients in group 1 and 12 patients in group 2 had completed their 2nd cycle of treatment, and twenty-one in group1 and 1 in group 2 their 4th cycle. Safety: The major toxicity related to study drug was neutropenia. Among 73 patients with preliminary safety data available, two patients had Grade 3 febrile neutropenia, and 31 had Grade 3 or 4 neutropenia or leukopenia. The other Grade 3 toxicities encountered in more than two patients were dehydration (4 patients) and dyspnea (4 patients). Grade 3 peripheral neuropathy was reported in 2 patients. Efficacy: At the end of cycle four there were 10 (15.2%) confirmed partial responses (PRs) out of 66 evaluable patients in group 1, and 1 confirmed PR (5.6%) out of 18 evaluable patients in group 2. The median duration of confirmed responses was 113 days. Conclusions: Based on the safety and efficacy in this refractory breast cancer population, E7389 appears to be a therapy worthy of continued investigation in patients with heavily pretreated breast cancer. In order to comply with the current demand for individualized cancer care, bio-markers which would predict the sensitivity to E7389 are being searched in the tumor samples of the patients in the current and forthcoming studies. [Table: see text]