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.

Adjuvant chemotherapy, Breast cancer, Cohort study, Genomic test, MammaPrint, Risk assessment,
The Breast
Erasmus MC: University Medical Center Rotterdam

Groenendijk, F.H. (Floris H.), Jager, 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