Resistance to HER2 inhibitors: is addition better than substitution? Rationale for the hypothetical concept of drug sedimentation.

Twenty years were passed between the discovery of oncogene HER2, the description of its implication in mammary carcinogenesis, and the development of specific targeted therapies. To date, trastuzumab and lapatinib are the two anti-HER2 targeted therapies commonly used, demonstrating therapeutic effects. Although their clinical efficacy seems to be exclusively related to the amplification of the HER2 gene or to the overexpression of the protein, these factors are not sufficient since tumors can develop resistance. Because of a better knowledge in those mechanisms of resistance, novel therapeutic agents could help to bypass them. How should these be used with respect to current anti-HER2 targeted therapies? Recent notions such as oncogene addiction, tumor cell dormancy and residual disease led us to propose a new entity that we named the "sedimentation strategy", in which distinct targeted approaches are summed during the treatment of metastatic breast cancer patients.