Detection of micrometastatic breast cancer by means of real time quantitative RT‐PCR and immunostaining in perioperative blood samples and sentinel nodes

Abstract

The aim of our study was to detect micrometastatic breast cancer by epithelial glycoprotein‐2 (EGP‐2) and cytokeratin 19 (CK19), using immunostaining and real time quantitative reverse transcriptase‐polymerase chain reaction (qRT‐PCR). Fifty‐eight breast cancer patients, 52 primary tumors, 75 sentinel nodes (SN) and 149 peripheral blood (PB) samples (from before, during and 4 days after operation) were examined. Immunostaining was performed with antibodies directed against EGP‐2 and CK19. Detection limits were one Michigan Cancer Foundation‐7 (MCF‐7) breast cancer cell line cell/2.10⁶ leukocytes (immunostaining) and one MCF‐7 cell/10⁶ leukocytes qRT‐PCR. Control noncancer lymph nodes (n = 10) showed nonspecific CK19 staining, but were qRT‐PCR negative; control healthy volunteer PB (n = 11) was always negative. Primary tumor samples, all positive with immunostaining, showed a wide variation of EGP‐2 (>10⁴ fold) and CK19 mRNA expression (>10³ fold). SN (n = 19) from 16 patients were tumor‐positive with routine haematoxylin‐eosin (H&E) and/or immunostaining. SN tumor presence was positively correlated to qRT‐PCR expression, but 3 tumor‐positive SN were false negative with qRT‐PCR. Three SN were qRT‐PCR positive, while tumor negative with H&E and/or immunostaining. No immunostaining positive PB was observed, but 19 patients (33%) had one or more qRT‐PCR positive PB samples. We concluded that primary tumors have varying expressions of EGP‐2 and CK19 mRNA. Both markers can be used in qRT‐PCR to obtain adequate sensitivity for single tumor cell detection. In SN, immunostaining appears more sensitive/specific than H&E or qRT‐PCR for tumor detection. No immunostaining positivity was found in PB, while 33% of patients had qRT‐PCR positive PB. The clinical value of these findings will have to be clarified.