Measurement of human epidermal growth factor receptor type-2 extracellular domain and cancer antigen 15-3 levels in needle washout fluid: a potential adjunct to the cytological diagnosis of breast cancer.

To determine whether the measurement of biomarkers in the needle washout fluid after fine needle aspiration cytology could strengthen cytological diagnosis, 29 benign lesions, 26 ductal carcinomas in situ (DCIS), and 95 invasive carcinomas of the breast were analyzed. Immediately after the aspiration samples were expelled onto glass slides, the needle was rinsed out with 2 ml of saline. Human epidermal growth factor receptor two extracellular domain (HER2-ECD) and cancer antigen 15-3 (CA 15-3) in the washout fluid were measured using chemiluminescence. The measuring limit for HER2-ECD (0.5 ng/ml) and that for CA 15-3 (4 U/ml) were used as the cutoff values, respectively. The proportion of patients with positive HER2-ECD values was 6.9% in cases of benign lesions, 26.9% in DCIS, and 10.5% in invasive carcinomas. The proportion of patients with positive CA 15-3 values was 6.9% in cases of benign lesions, 42.3% in DCIS, and 10.5% in invasive carcinomas. The proportion of patients with any biomarker elevation was 6.9% in cases of benign lesions, 46.2% in DCIS, and 15.8% in invasive carcinomas. Thus, biomarker elevation was most frequent in cases of DCIS, followed by invasive carcinomas (P < 0.01). HER2-ECD values over 6 ng/ml or CA 15-3 values over 25 U/ml were seen exclusively in cases of DCIS or invasive ductal carcinomas with an extensive intraductal component. If the biomarker status is included, 5 of 12 cases of DCIS with equivocal cytology categories would be upgraded. Further clinicopathological validation is necessary before applying this new approach to the clinical setting.