A meta-analysis of receptor status discordance between primary breast cancer and metastases.
546 Background: There is an increasing awareness that biology of breast cancer may evolve over time. The discordance in estrogen (ER), progesterone (PgR) and HER2 receptor status between primary breast cancer and metastases is being intensively investigated and a large amount of data has been produced. However, results from different studies seem to be conflicting and heterogeneous. To highlight this issue, a meta-analysis of published data was performed. Methods: A literature search was performed with Medline. All studies published from 1983 to 2011 comparing changes inER, PgR and/or HER2 status in patients with matched breast primary and recurrent tumors were included. We used random-effects models to estimate pooled discordance proportions. Results: We selected 42 articles, mostly reporting retrospective studies. Twenty-eight, 20 and 27 articles were focused on ER, PgR and HER2 changes, respectively. A total of 2806 tumors were evaluated for ER discordance, 1809 for PgR discordance and 2801 for HER2 discordance. The heterogeneity between study-specific discordance proportions was high (I2 >75%, p<0.0001) for ER, PgR and HER2. Pooled discordance proportions were 20% (95% CI: 16-25%) for ER, 33% (95% CI: 28-38%) for PgR and 9% (95% CI: 6-12%) for HER2. Pooled proportions of tumors shifting from positive to negative and from negative to positive were 24% and 12% for ER (p=0.0115), respectively. The same figures were 44% and 15% for PgR (p<0.0001), and 14% and 6% for HER2 (p=0.04). Conclusions: To our knowledge, this is the first meta-analysis addressing this topic. The findings strengthen the concept that changes in receptor expression may occur during the natural history of breast cancer and therefore clinical implications with possible impact on treatment choice cannot be excluded. However, the high heterogeneity observed in our analysis may explain the disagreement among oncologists on performing a reassessment of the biological features. In our opinion, only high-powered prospective and randomized trials could clarify the controversies in this field.