On July 10, 2017 ASCO published an update to its Breast Cancer Biomarkers Guidelines specifically to include Mammaprint (Agendia, Irvine, CA). The update authors refer to the NEJM August 16 publication of results from the MINDACT (Microarray in Node-Negative and 1 to 3 Positive Lymph Node Disease May Avoid Chemotherapy) trial as the signal prompting the update. Patients with low MammaPrint risk did not benefit from chemotherapy if they were node negative or even if they had 1-3 nodes positive. The authors distinguish two classes of clinical risk and organize their recommendations with reference to high and low clinical risk (see table below). Among other less critical reasons, this distinction was included because patients at high genomic (MammaPrint) risk did not benefit from chemotherapy if they had low clinical risk.
From the abstract:
An expert panel reviewed the results of the MINDACT study along with other published literature on the MammaPrint assay to assess for evidence of clinical utility.
If a patient has hormone receptor–positive, human epidermal growth factor receptor 2 (HER2)– negative, node-negative breast cancer, the MammaPrint assay may be used in those with high clinical risk to inform decisions on withholding adjuvant systemic chemotherapy due to its ability to identify a good-prognosis population with potentially limited chemotherapy benefit. Women in the low clinical risk category did not benefit from chemotherapy regardless of genomic MammaPrint risk group. Therefore, the MammaPrint assay does not have clinical utility in such patients. If a patient has hormone receptor–positive, HER2-negative, node-positive breast cancer, the MammaPrint assay may be used in patients with one to three positive nodes and a high clinical risk to inform decisions on withholding adjuvant systemic chemotherapy. However, such patients should be informed that a benefit from chemotherapy cannot be excluded, particularly in patients with greater than one involved lymph node. The clinician should not use the MammaPrint assay to guide decisions on adjuvant systemic therapy in patients with hormone receptor–positive, HER2-negative, node-positive breast cancer at low clinical risk, nor any patient with HER2-positive or triple-negative breast cancer, because of the lack of definitive data in these populations.