Methods and goals for the use of in vitro and in vivo chemosensitivity testing

Sensitive, specific, and accurate methods to assay chemosensitivity are needed to (1) screen new therapeutic agents, (2) identify patterns of chemosensitivity for different tumor types, (3) establish patterns of cross-resistance and sensitivity in treatment of naïve and relapsing tumors, (4) identify genomic and proteomic profiles associated with sensitivity, (5) correlate in vitro response with preclinical in vivo effects and clinical outcomes for a particular therapeutic agent, and (6) tailor chemotherapy regimens to individual patients. Various methods are available to achieve these end points, including several in vitro clonogenic and proliferation assays, cell metabolic activity assays, molecular assays to monitor expression of markers for responsiveness, drug resistance, and for induction of apoptosis, in vivo tumor growth and survival assays in metastatic and orthotopic models, and in vivo imaging assays. The advantages and disadvantages of the specific assays are discussed. A summary of research questions related to chemosensitivity testing is also included.