Tremelimumab is a fully human monoclonal antibody specific for CTLA4 with single-agent activity in certain tumors, but has not been evaluated in patients with breast cancer.

In a phase 1 study, 26 patients with advanced, hormone-responsive breast cancer received tremelimumab (3 to 10 mg/kg) every 28 days (Q28D) or every 90 days (Q90D) plus exemestane 25 mg daily. The objectives were to determine safety and the maximum tolerated dose (MTD) of tremelimumab with exemestane, and secondarily, to assess tumor response, pharmacokinetics, and immune pharmacodynamics.

Most treatment-related adverse events were mild to moderate with the most common being diarrhea (46% of patients), pruritus (42%), constipation (23%), and fatigue (23%). Dose-limiting toxicities were transient serum transaminase elevations (1 patient) and diarrhea (4 patients). The MTD of tremelimumab with exemestane was 6 mg/kg Q90D. Among 13 patients treated at the MTD, none developed grade 3 or 4 treatment-related diarrhea. No pharmacokinetic interaction was observed between tremelimumab and exemestane. The best overall response was stable disease for >/= 12 weeks in 11 patients (42%). Treatment was associated in most patients with increased peripheral CD4+ and CD8+ T cells expressing inducible costimulator (ICOS) and a marked increase in the ratio of ICOS+ T cells to FoxP3+ regulatory T cells.

Tremelimumab plus exemestane is tolerable in patients with hormone-responsive advanced breast cancer. Treatment is associated with increased ICOS+ T cells, which likely signals immune activation secondary to CTLA-4 blockade.

PMID: 20479064 [PubMed - as supplied by publisher] Source: National Library of Medicine.