Molecular subtypes of breast cancer: secular improvement in prognosis

Abstract

Abstract Background: Prognostic improvement over time may differ between molecular breast cancer subtypes. Methods: Molecular subtypes of breast cancer (denoted Luminal A, Luminal B (HER2-), Luminal B (HER2+), HER2 type, and Triple negative) were determined by immunohistochemistry and in situhybridization applied to tissue microarrays (TMA) from archival diagnostic material. Analyses included 1957 incident cases diagnosed in three population studies over more than 30 years of observation. To study differences in prognosis over time, we compared 10-year risk of death for each subtype between specified diagnostic periods. Results: Luminal A was most frequent (47.9%) followed by Luminal B (HER2-) (28.2%), Luminal B (HER2+) (9.0%), Triple negative (9.2%) and the HER2 subtype (5.7%). Between 1990 and 2000, the 10-year risk of death from breast cancer decreased substantially for each subtype, compared to before 1990. After 2000, the decrease continued for Luminal A and HER2 patients, but there was no further decrease for Triple negative patients. Conclusion: The observed improvement in prognosis during the 1990s may primarily be attributed to modern oncological treatment. After 2000, the improvement for Luminal A coincides with implementation of organized mammography screening, whereas the strong improvement for HER2 patients may be due to novel targeted treatment.