Aim 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. Methods 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). Results 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. Conclusions 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.

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Keywords Adjuvant chemotherapy, Breast cancer, Cohort study, Genomic test, MammaPrint, Risk assessment
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Journal The Breast
Groenendijk, F.H. (Floris H.), Jäger, A, Cardoso, F. (Fatima), & van Deurzen, C.H.M. (2018). A nationwide registry-based cohort study of the MammaPrint genomic risk classifier in invasive breast cancer. The Breast, 38, 125–131. doi:10.1016/j.breast.2017.12.015