Comparison of primary breast cancer and paired metastases: biomarkers discordance influence on outcome and therapy

Aim: Discordance between primary tumor and paired metastases biology has been widely detected in metastatic breast cancer. The aim of this study was to evaluate the prognostic impact of Ki67, estrogen receptor (ER), progesterone receptor (PR) and HER2 discordance. Methods: We retrospectively analyzed a cohort of 544 patients affected by metastatic breast cancer. Variation in ER, PR, Ki67 and HER2 expression between primary site and recurrence was tested through the McNemar test. Results: A significant variation was observed in respect to ER, PR and Ki67 status (12.65%, p = 0.0072; 49.71%, p < 0.0001; 35%, p < 0.0001, respectively). Among patients with ER or PR discordance, the driver of therapeutic decisions was the ER status. Moreover, we observed a therapy-related reduction of ER in taxanes or aromatase inhibitors-exposed patients (odds ratio: 3.59; 95% CI: 1.66-7.77; p = 0.001 and odds ratio: 2.07; 95% CI: 0.96-4.44; p = 0.06, respectively). Conclusion: Biopsy of metastatic lesions may influence the decisionmaking process translating into better outcome.