Molecular changes in the primary breast cancer versus the relapsed/metastatic lesion from a large population-based database and tissue microarray series

1000 Background: Relapsed/metastatic breast cancers are presumed to have the same predictive factors as the initial primary tumour. As such, the majority of patients do not have additional biopsies performed at the time of relapse. Recent small studies have suggested that a significant proportion of relapsed lesions may have a change in the hormone receptor and/or HER2 receptor status from the original tumour. We sought to compare the hormonal and HER2 receptor status of relapsed/metastatic breast cancer tumours with those of the original tumour from a large population-based database and tissue microarray (TMA) cohort. Methods: Using the BCCA Breast Cancer Outcomes Unit Database from 1986–1992, patients with biopsy proven relapses were identified. These identified patients were linked to a current large TMA series (n=4,444) of primary breast cancers. Charts were reviewed, and available tissue blocks of the relapsed/metastatic cancer were requested and collected. An additional TMA was created of the relaps...