Genomic Grade Index: An important tool for assessing breast cancer tumor grade and prognosis

Different multi-gene expression signatures have been shown to outperform classic histopathologic variables and therefore represent an important step towards personalizing breast cancer treatment. In particular, gene profiles overcome many of the limitations observed with classic histopathologic variables. The Genomic Grade Index (GGI) is a gene expression signature developed to better define histologic grade assessment. GGI divides classic histologic grade into low and high risk, instead of grades 1, 2 and 3. The ability of GGI to predict response to chemotherapy and separate hormone receptor positive breast cancer subtypes has also been demonstrated. This article critically reviews the limitations inherent in classic histologic grade evaluation; it also reviews the process of gene signature development in general and then focuses on GGI, its biologic significance, comparison with different gene signatures, and its applicability to clinical practise.