Over 210,000 women will develop breast cancer each year and approximately 41% will be postmenopausal women with estrogen receptor expressing, node negative breast cancer for which Mammostrat testing is indicated. The standard of care for most of these patients is surgery to remove tumor followed by hormone signaling targeted therapy (e.g. tamoxifen or aromatase inhibitors).

	Figure. AGI's approach takes advantage of insights from gene expression studies that established that breast cancer patients have many different subtypes of tumors (depicted by various colored boxes in the figure). Current biomarkers and therapeutic approaches distinguish some of this tumor diversity (e.g. estrogen receptor and ERBB2 biomarkers) but some patients with estrogen receptor expressing tumors (depicted as yellow, blue, and green subtypes), face difficult decisions about treatment choices not served by current diagnostic IHC tests. AGI's Mammostrat test classifies these patients into groups of low-, moderate-, and high-risk for breast cancer recurrence. Patients and oncologists can use this risk information to help select amongst treatment options.

The prognosis for this group of early stage, estrogen receptor positive breast cancer patients is considered favorable with approximately 90% or more of these patients surviving five years and longer. However, several studies have demonstrated that outcomes can be further improved by treatment with cytotoxic chemotherapy. Since it is clear that most patients will remain disease free in the absence of additional therapy it is likely that cytotoxic therapy is only important for a small subset of these early-stage cancers. Since chemotherapy comes with difficult side effects (e.g. nausea, hair loss, severe fatigue) and long term risk of cardiovascular complications and secondary tumors, the decision whether to use adjuvant chemotherapy is difficult and controversial. The potential benefit of using Mammostrat testing is to identify those patients at high risk of cancer recurrence and therefore more likely to benefit from additional chemotherapy as opposed to those patients at low risk of recurrence who may choose to forgo chemotherapy.