Phase I/II study of sorafenib with anastrozole in patients with hormone receptor positive aromatase inhibitor resistant metastatic breast cancer.

We evaluated the use of sorafenib to overcome resistance to aromatase inhibitors (AIs) in patients with metastatic breast cancer who had disease recurrence or progression while on AIs. We performed a multi-institution phase I/II study of sorafenib and anastrozole 1 mg daily in 35 postmenopausal females with hormone receptor positive metastatic breast cancer resistant to AIs. Primary objectives were to determine the dose of sorafenib in conjunction with anastrozole and the clinical benefit rate (CBR) (complete response [CR], partial response [PR], or stable disease [SD] ≥ 24 weeks). Secondary objectives were to determine toxicity and to evaluate if response was associated with change in number of circulating endothelial cells or circulating endothelial progenitor cells. Based on the phase I portion, sorafenib 400 mg twice daily was selected as the phase II dose. Among 35 patients, 7 had SD ≥ 24 weeks, 1 had PR ≥ 24 weeks, and 14 had progressive disease (PD) ≤ 24 weeks, corresponding to a CBR of 23%. The most common adverse events (all; Grade 3/4) were fatigue (66%; 17%), diarrhea (63%; 6%), nausea (60%; 9%), and hand-foot syndrome (57%; 34%). Dose reduction occurred in 77% of the patients and 31% came off study due to toxicity. The combination of sorafenib and anastrozole demonstrated a 23% CBR in patients with hormone receptor positive, AI-resistant metastatic breast cancer, which may be attributable to the restoration of sensitivity to AIs. Toxicities occurred frequently resulting in a high rate of discontinuation.

A prospective randomized pilot study to evaluate predictors of response in serial core biopsies to single agent neoadjuvant doxorubicin or paclitaxel for patients with locally advanced breast cancer.

INTRODUCTION: Response to neoadjuvant chemotherapy for locally advanced breast cancer can be correlated with long-term outcomes. Surrogate end-point biomarkers may be used to assess response to the treatment. Most reported studies assessed the effects of combination chemotherapy. We assessed the feasibility of obtaining serial core breast biopsies, and correlated rates of apoptosis, proliferation, and expression of related proteins at baseline, during, and after neoadjuvant single agent chemotherapy for locally advanced breast cancer with response. EXPERIMENTAL DESIGN: Women with a histologically confirmed unresected T(3) or T(4) infiltrating carcinoma of the breast were eligible. The first 20 patients received three cycles of doxorubicin 90 mg/m(2) followed by three cycles of paclitaxel 250 mg/m(2), or the reverse. Nine women received four cycles of each (doxorubicin 60 mg/m(2) and paclitaxel 175 mg/m(2)). Cycles were administered 14 days apart with filgastrim. End points included: (a). clinical and pathological response; (b). serial apoptotic [terminal deoxynucleotidyl transferase (Tdt)-mediated nick end labeling] and proliferation (immunohistochemistry, IHC) rates; and (c). expression (IHC) of estrogen receptor, HER2, bcl2, and p53. RESULTS: From April 1997 to June 2001, 29 women were randomized. Twelve patients (42%) had a clinical complete response (cCR), and 16 (55%) had a clinical partial response. Five women (17%) had a pathological complete response, 7 (24%) had microscopic residual disease, and 17 (58%) had macroscopic residual disease. Higher baseline apoptosis and proliferation were associated with an improved pathological response (P = 0.006 and 0.003, respectively). Among 14 evaluable patients, apoptosis increased in women who had a cCR to the first agent but not in women without a cCR. Estrogen receptor-positive patients had a worse pathological response (P = 0.004). CONCLUSIONS: The selected regimen is efficacious. It is feasible to obtain serial core biopsies that are informative for studies of apoptosis and IHC. This clinical design can serve as a model for combining standard chemotherapy and novel agents.

Active tamoxifen metabolite plasma concentrations after coadministration of tamoxifen and the selective serotonin reuptake inhibitor paroxetine.

BACKGROUND: Tamoxifen, a selective estrogen receptor modulator (SERM), is converted to 4-hydroxy-tamoxifen and other active metabolites by cytochrome P450 (CYP) enzymes. Selective serotonin reuptake inhibitors (SSRIs), which are often prescribed to alleviate tamoxifen-associated hot flashes, can inhibit CYPs. In a prospective clinical trial, we tested the effects of coadministration of tamoxifen and the SSRI paroxetine, an inhibitor of CYP2D6, on tamoxifen metabolism. METHODS: Tamoxifen and its metabolites were measured in the plasma of 12 women of known CYP2D6 genotype with breast cancer who were taking adjuvant tamoxifen before and after 4 weeks of coadministered paroxetine. We assessed the inhibitory activity of pure tamoxifen metabolites in an estradiol-stimulated MCF7 cell proliferation assay. To determine which CYP isoforms were involved in the metabolism of tamoxifen to specific metabolites, we used CYP isoform-specific inhibitors. All statistical tests were two-sided. RESULTS: We separated, purified, and identified the metabolite 4-hydroxy-N-desmethyl-tamoxifen, which we named endoxifen. Plasma concentrations of endoxifen statistically significantly decreased from a mean of 12.4 ng/mL before paroxetine coadministration to 5.5 ng/mL afterward (difference = 6.9 ng/mL, 95% confidence interval [CI] = 2.7 to 11.2 ng/mL) (P =.004). Endoxifen concentrations decreased by 64% (95% CI = 39% to 89%) in women with a wild-type CYP2D6 genotype but by only 24% (95% CI = 23% to 71%) in women with a variant CYP2D6 genotype (P =.03). Endoxifen and 4-hydroxy-tamoxifen inhibited estradiol-stimulated MCF7 cell proliferation with equal potency. In vitro, troleandomycin, an inhibitor of CYP3A4, inhibited the demethylation of tamoxifen to N-desmethyl-tamoxifen by 78% (95% CI = 65% to 91%), and quinidine, an inhibitor of CYP2D6, reduced the subsequent hydroxylation of N-desmethyl-tamoxifen to endoxifen by 79% (95% CI = 50% to 108%). CONCLUSIONS: Endoxifen is an active tamoxifen metabolite that is generated via CYP3A4-mediated N-demethylation and CYP2D6-mediated hydroxylation. Coadministration of paroxetine decreased the plasma concentration of endoxifen. Our data suggest that CYP2D6 genotype and drug interactions should be considered in women treated with tamoxifen.