Double-blind, placebo-controlled, multicentric randomized phase IIb neoadjuvant study of letrozole-lapatinib in postmenopausal HER2-negative, hormone receptor-positive operable breast cancer

Background: The crosstalk between the ER pathway and erbB receptor family is emerging as a mechanism of resistance to hormonal therapy. The combination of lapatinib-letrozole might prevent or delay the development of endocrine resistance. On these premises we have designed a multicentric phase IIb randomized, double-blind, placebo controlled study to evaluate the clinical and biological effects of combined letrozole+lapatinib/placebo as neoadjuvant therapy in previously untreated ER+ve/HER2-ve breast cancer patients. Primary aim is the percentage of breast clinical response, as measured by ultrasonography (US). Secondary aims include pathologic response, percentage of breast conserving surgery, modulation of Ki67 and HER2/EGFR pathways, and gene expression analysis. Methods: After diagnostic core biopsy, patients were randomized to letrozole 2.5 mg continuous daily dosing (CDD) + lapatinib 1500mg CDD or to letrozole- placebo, given for 24 weeks before surgery. Results: As of October 2010, the planned accrual has been completed. Ninety-two postmenopausal women have been randomized. Patient characteristics were as follows: median age 68 yrs (range 48-89 yrs); stage at diagnosis: IIA 49%; IIB 41%, IIIA 10%. Median ER expression 95% (range 30-100%); median PgR expression 68% (range 0-100%). At diagnosis, mean US tumor size was 3 cm (range 1.2-8 cm). Seventy-one patients are evaluable so far. The ORR (PR + CR) by US at the completion of therapy was 61%; SD was observed in 27% of the patients. Four patients experienced PD. Five patients prematurely discontinued therapy due to toxicity (n=1), consent withdrawal (n=3) or lost to follow up (n=1). No change in mean LVEF was observed at the 3- and 6-month evaluations. The data will be unblinded by April 2011. Conclusions: Preliminary blinded results suggest that the combination of letrozole+lapatinib/placebo is associated with clear tumor downstaging. Final unblinded results per treatment arm, including pathologic response, clinical response by centralized review and biomarker analyses will be presented at the meeting.