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Complete Responses Reported in Breast Cancer Patients Treated With Sacituzumab Govitecan

Phase II study achieves 76% disease control rate

Of 49 patients with metastatic triple-negative breast cancer (TNBC) evaluated for their response to treatment with sacituzumab govitecan (Immunomedics, Inc.) in a phase II study, 15 (31%) showed a reduction in tumor size of 30% or more. These patients included two with a complete response. Adding the 22 patients with responses of between less than 30% tumor shrinkage and less than 20% tumor increase, the disease control rate was 76%.

Sacituzumab govitecan also produced a significant duration of response in the responding patients. Measured as the time it takes from the beginning of sacituzumab govitecan treatments to when the cancer progresses, the median progression-free survival (PFS) for the 48 patients who received the optimal doses of 8 or 10 mg/kg was 6.0 months. Importantly, 63% of patients (22/35) had time-to-progression that was longer than their last therapy.

The results were presented at the 2015 annual meeting of the American Society of Clinical Oncology.

TNBCs are negative for estrogen and progesterone receptors, as well as for human epidermal growth factor receptor 2 (HER2). These malignancies comprise approximately 15% to 20% of all invasive breast cancers and are more prevalent in young and African-American women. Despite the fact that initial responses with chemotherapy are high, TNBC characteristically has a high recurrence rate and is perhaps the most difficult type of breast cancer to treat successfully with current cytotoxic agents. Progression-free survival in the range of 2.9 to 3.7 months has been reported in recent clinical studies in patients with metastatic TNBC after chemotherapy. Currently, no targeted treatments are available for the disease.

In the new study, a total of 58 patients with relapsed or refractory metastatic TNBC received sacituzumab govitecan once a week for 2 weeks in 21-day cycles. Despite repeated dosing, sacituzumab govitecan was well tolerated by patients. At the optimal doses of 8 and 10 mg/kg, transient neutropenia was the major grade-3 or -4 adverse events, with a 26% occurrence rate. Grade-3 diarrhea was minimal, reported by only 2% of patients.

Sacituzumab govitecan is a first-in-class antibody–drug conjugate developed by conjugating the moderately toxic drug SN-38 site-specifically and at a high ratio of drug to antibody to a humanized antibody that targets the cell-surface TROP-2 receptor, which is expressed by many solid cancers. SN-38 is the active metabolite of irinotecan (Camptosar, Pfizer), which is used to treat certain solid cancers, particularly metastatic colorectal cancers, as a part of combination therapies.

The FDA has designated sacituzumab govitecan as a “fast track” investigational treatment for patients with TNBC who have failed prior therapies for metastatic disease and for patients with small-cell or non–small-cell lung cancers.

Source: PipelineReview, Inc.; June 1, 2015.

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