A nationwide registry-based cohort study of the MammaPrint genomic risk classifier in invasive breast cancer

To evaluate the use of the MammaPrint assay, a 70-gene risk signature for early breast cancers, and to correlate genomic risk stratification with individual clinicopathological parameters and clinical risk as assessed by Adjuvant! Online.

A Dutch Pathology Registry (PALGA)-based cohort study consisting of 1916 patients for which 1946 MammaPrint assay results were synoptically reported from 2013 to 2016. We could retrospectively assess clinical risk for 1146 tumors (58.9%) using Adjuvant! Online (version 8.0 with HER2 status) and for 1155 tumors (59.4%) using PREDICT (version 2.0).

Adjuvant! Online classified 718 tumors (62.7%) as clinical low risk and 428 tumors (37.3%) as clinical high risk. MammaPrint classified 1206 tumors (62.0%) as genomic low risk and 740 tumors (38.0%) as genomic high risk. Genomic risk stratification was significantly associated with histological subtype and grade (P < .001), hormonal receptor status (P < .001), presence of lymphovascular invasion (P = .001) and nodal status (P = .002), whereas no association was found with tumor size (P = .541). MammaPrint classified 52.6% of clinical high risk tumors (N = 428) as genomic low risk. This percentage was highest (67.3%) in clinical high risk ER-positive/HER2-negative grade 1-2 tumors (N = 282). Correlation between predicted overall survival benefit from adjuvant chemotherapy (PREDICT V2.0) and genomic risk distribution was almost linear.

This study showed that MammaPrint classified 52.6% of clinical high risk tumors as genomic low risk. In the Netherlands, 62.7% of the MammaPrint assays from 2013 to 2016 were performed on clinical low risk tumors, although recent International Guidelines recommend its use in clinical high and intermediate risk tumors.