In 2002, Stanford researchers became the first to use gene expression profiling to predict cancer outcomes.

The research approach identified prognostic signatures based on defining gene sets involved in a biological process or specific environmental condition that was suspected of influencing treatment response or patient outcome.

In this approach, in vitro gene expression profiling was used to identify gene sets that play an important role in a specific biological process. The identified gene set wass then applied to gene expression data from patients to evaluate its prognostic value. This approach hada more broad application because the gene sets can be applied in almost every patient group.