Phase I trial of escalating doses of weekly everolimus (RAD001) in combination with docetaxel for the treatment of metastatic breast cancer (MBC)

1066 Background: Inhibition of mTOR with everolimus (E) may improve efficacy in combination with docetaxel (D), but both drugs are metabolized by CYP3A4, thus a pharmacokinetic (PK) interaction may also exist.

METHODS: 15 patients (pts) with MBC were treated with docetaxel and everolimus using the continuous reassessment method (CRM) to determine maximum tolerated dose (MTD). Docetaxel doses were 40-75 mg/m(2) IV on day 1 of a 21 day cycle. Everolimus doses were 20-50 mg PO on days 1 and 8 of a 21 day cycle (except cycle 2, where only day 8 was given to allow single agent PK analyses of both drugs). Response was measured every 2 cycles using RECIST.

RESULTS: Median age= 58 years and 77% of pts had >2 prior chemotherapies for MBC. Initially 2 of 2 pts treated (D= 75 mg/m2, E= 30 mg) developed DLT (neutropenic fever/infection), prompting a mandatory PK evaluation for all pts enrolled in subsequent cohorts. A second cohort of 3 patients (D=60 mg/m2, E=20mg) had no DLT, but no pts received day 8 of E due to grade 3-4 neutropenia. PK analyses demonstrated a 42% lowered (-42%) D clearance at the 60 mg/m2 in the presence of E (n=1). Subsequent cohorts were accrued at D=40 mg/m2 with escalating doses of E (Table). For the entire group, an 18% decrease (-18%) in D clearance was observed when D was administered concomitantly with E. High interpatient variability of D clearance was observed (range +16% to -135%). No pts had CR/PR, but 6 had SD>4 cycles and 2 had SD=8 cycles.

CONCLUSIONS: Weekly everolimus appears to cause widely variable and unpredictable changes in docetaxel clearance making this combination unfeasible. [Table: see text] No significant financial relationships to disclose.