Wang SY, et al. - Researchers investigated the reasons for incongruent results shown by previous studies examining cost effectiveness of the 21-gene assay (Oncotype DX [ODX]) for women with hormone receptor–positive, early-stage breast cancer. In a systematic literature review, they determined the impact of the structure of cost-effectiveness analysis (CEA) modeling, the assumptions of the models, and the selection of input parameters on cost-effectiveness estimates. The heterogeneous effect of ODX on chemotherapy use was ignored by most of the studies and ODX was favored by industry-funded studies. Overall, ODX was shown to be cost effective in a majority of published analyses but they incorporated study designs that can increase the risk of bias.