Lapatinib enhances herceptin-mediated antibody-dependent cellular cytotoxicity by up-regulation of cell surface HER2 expression.

Background: Although it was previously reported that lapatinib combined with Herceptin improved the progression-free survival rate compared with lapatinib alone for patients with Herceptin-refractory HER2-positive metastatic breast cancer, the mechanism is purported to be an antiproliferative effect relating to the synergism of these two agents.

Methods: We evaluated how lapatinib interacts with Herceptin in HER2-positive breast cancer, with a particular focus on Herceptin-mediated antibody-dependent cellular cytotoxicity (ADCC).

Results: In an in vitro assay, lapatinib induced HER2 expression at the cell surface of HER2-positive breast cancer cell lines, leading to the enhancement of Herceptin-mediated ADCC. Furthermore, we present a case report in which a second Herceptin treatment following lapatinib resulted in the marked shrinkage of multiple metastatic tumors in HER2-positive breast cancer.

Conclusions: Lapatinib may have the potential to convert Herceptin-refractory to Herceptin-sensitive tumors in HER2-positive breast cancer by up-regulation of the cell surface expression of HER2.