Sentinellymph node (SLN) biopsy is considered a highly accurate and very economic method of assessing the axillary nodal status in breast cancer patients. Recently immunohistochemical (IHC) staining and reverse transcriptase polymerase chain reaction (RT-PCR) are commonly used to evaluate micrometastasis in the sentinel lymph node. However, most of the RT-PCR studies have been performed using fresh tissue. This study was conducted to assess micrometastasis in clinically node-negative breast cancer by using RT-PCR technique on the paraffin embedded sentinel lymph nodes.

Sixty patients who undergone SLN biopsy followed by axillary lymph node dissection due to breast carcinoma were evaluated from February 2000 to January 2001 at the Breast Cancer Center, Department of Surgery, Yongdong Severance Hospital. Serial sections were made from all sentinel lymph nodes for the H&E staining and for the IHC staining with monoclonal anti-cytokeratin antibody. RNA was extracted from the paraffin embedded sentinel lymph nodes and RT-PCR was performed using cytokeratin 19 mRNA, MUC-1 mRNA, and MAGE-A3 mRNA.

In 32 out of 60 cases, β-actin mRNA was detected after RT-PCR. and the 28 cases which had no product after RT-PCR for, β-actin were excluded from this study. Twenty five cases showed as being metastasis positive and 7 cases showed as being metastasis negative by serial section (SS) H&E staining. Three out of 25 negative cases tested for by 55 H&E staining were found to be positive by IHe. Ten, six and, eight cases out of the 25 negative cases tested for by SS H&E were found to be positive by RT-PCR for cytokeratin 19, MUC-1.and MAGE-A3, respectively. Among the 22 cases that were found to be negative by both SS H&E staining and IHC staining, 9, 4, and 6 cases were converted to positive by RT-PCR for cytokeratin 19, MUC-1, and MAGE-A3, respectively. Using the combination of two or three markers for performing RT-PCR was more sensitive than any single marker to detect micrometastasis (p<0.05).

Even though we failed to extract RNA in 46% of the paraffin embedded tissues, it may be possible to detect micrometastasis by using RT-PCR with the paraffin embedded tissue. RT-PCR is far more sensitive than IHC for detecting microme tastasis, and when we combine multiple markers, the detection rate is higher than for anyone marker.