According to a study published in the Journal of the National Cancer Institute, Lapatinib delayed tumor development in a mouse model of hormone receptor-negative breast cancer and reduced the number of tumors per animal compared with mice treated only with vehicle (an inert solution lacking lapatinib).

Lapatinib is a small-molecule inhibitor that blocks the tyrosine kinase activities of epidermal growth factor receptor and ErbB2, both of which promote cell proliferation and are associated with tumor formation. MMTV-erbB2 transgenic mice, which express wild-type ErbB2 in mammary tissue, develop mammary tumors that are estrogen receptor (ER)–negative and ErbB2-positive by 14 months of age.

To examine whether lapatinib may prevent development of breast tumors that are driven by ErbB2, Powel H. Brown, M.D., Ph.D., of Baylor College of Medicine in Houston, and colleagues treated MMTV-erbB2 transgenic mice with either high- or low-dose lapatinib or vehicle alone.

By 328 days after the start of treatment (age of 418 days), five of 16 mice, or 31 percent, treated with high-dose lapatinib had developed mammary tumors compared with 100% of the 17 mice treated with vehicle alone. The lapatinib-treated mice developed statistically significantly fewer tumors per animal than the vehicle-treated animals.

"Our results show that lapatinib suppresses the development of ER-negative ErbB2-positive invasive mammary tumors in MMTV-erbB2 mice," the authors conclude. "Thus, lapatinib may be useful for the prevention of ER-negative, ErbB2-positive mammary tumors in humans."

SOURCE:
Journal of the National Cancer Institute, online edition, January 13, 2009