Phase I clinical and pharmacokinetics study of high-dose toremifene in postmenopausal patients with advanced breast cancer*

Toremifene is an antiestrogen that binds strongly to estrogen receptors (ER). A total of 19 previously treated postmenopausal women with metastatic breast cancer whose performance status was good and whose ER status was positive or unknown were studied to determine the maximum tolerated dose of toremifene. Cohorts of patients received 200, 300, or 400 mg/m2 p.o. daily until relapse or unacceptable toxicity had occurred. Nausea, vomiting, and dizziness were dose-related. Three of five patients receiving 400 mg/m2 experienced moderate or severe vomiting and another developed reversible disorientation and hallucinations. Mild sweating, peripheral edema, vaginal discharge, and hot flushes were encountered at all doses. Reversible corneal pigmentation was identified in seven cases but was not of clinical importance. The pharmacokinetics of toremifene was studied weekly and in detail on day 42 using a high-performance liquid chromatographic (HPLC) assay that identified the parent compound and three active metabolites,N-desmethyltoremifene, (deaminohydroxy)toremifene, and didemethyltoremifene. Steady state was achieved at 1–3 weeks. The toremifene area under the curve and the maximal concentration were dose-dependent at high doses. The recommended phase II dose is 300 mg/m2 p.o. daily.