ERBB2 and breast cancer: Based on a systematic review of the literature, Carney et al [28] reported that the prevalence ofelevated serum HER2 ECD levels was approximately 18% (range0–38%) in primary breast cancer (2,623 women in 25 studies) butincreased to 43% (range 23–80%) in metastatic breast cancer(4,622 women in 45 studies).