Since there are currently no serologic tests for breast cancer, we wished to determine whether circulating levels of PLAC1 protein could serve as a biomarker in preoperative and pretreatment breast cancer subjects ranging from DCIS to early and late stage hormone-dependent, HER2+ or triple-negative disease, and whether it correlated with its expression in tumor biopsies. The gene discussed is ERBB2; the disease is breast cancer.