A series of multigene classifiers, prognostic and predictive tests have recently 
been introduced as potentially useful adjuncts for the management of recently 
diagnosed breast cancer patients. These tests have used both slide-based methods 
including immunohistochemistry and fluorescence in situ hybridization and 
nonmorphology driven molecular platforms including quantitative multiplex real 
time polymerase chain reaction and genomic microarray profiling. In this review, 
a series of partially and completely commercialized multigene assays are 
compared with the standard breast cancer clinico-pathologic variables and 
biomarkers and evaluated as to the level of their scientific validation, current 
clinical utility, regulatory approval status, and estimated cost-benefit. A 
comparison of the Oncotype Dx and MammaPrint assays indicates that the Oncotype 
Dx test has the advantages of an earlier commercial launch in the US, wide 
acceptance for payment by third party payors, the ease of use of formalin fixed 
paraffin embedded tissues, a recommendation as ready for use by the American 
Society of Clinical Oncology Breast Cancer Tumor Markers Update Committee, a 
continuous rather than dichotomous algorithm, inclusion of both estrogen 
receptor (ER) and human epidermal growth factor receptor 2 in the mRNA profile, 
an ability to serve as both a prognostic and predictive test for certain 
hormonal and chemotherapeutic agents, demonstrated cost-effectiveness in 1 
published study, and a high accrual rate for the prospective validation clinical 
trial (Trial Assigning Individualized Options for Treatment Rx). The MammaPrint 
assay has the advantages of a 510(k) clearance by the US Food and Drug 
Administration, a larger gene number which may enhance further utility, and the 
potentially wider patient eligibility including lymph node-positive, 
ER-negative, and younger patients being accrued into the prospective trial (the 
Microarray in Node-negative Disease may Avoid ChemoTherapy). A number of other 
assays have specific predictive goals most often focused on the efficacy of 
tamoxifen in ER-positive patients such as the Two-gene Ratio test and the 
Cytochrome P450 CYP2D6 genotyping assay.