Sentinel lymph node micrometastasis detection using immunohistochemistry and reverse transcription-polymerase chain reaction for cytokeratin 19 in breast cancer

11074 Background: In breast cancer, the sentinel lymph node (SLN) can be used to assess the axillary nodal status to guide the axillary surgery, tumor staging and adjuvant systematic therapy. Histology and immunohistochemistry (IHC) are currently the routine methods of SLN assay. The facts that about 30% of node-negative breast cancer patients relapse within five years and that micrometastasis were found in 9%∼30% negative lymph nodes when they were re-examined using serial sectioning suggest that current histological detection methods are inadequate for identifying metastatic tumor cells in lymph nodes. The primary objective of this study was to develop an assay by using a combination of reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry for cytokeratin 19 (KT19) expression in SLN. Methods:139 SLN samples were collected from 139 breast cancer patients undergoing SLN biopsy using Isosulfan Blue dye during modified mastectomy between June 2002 and June 2005. The SLNs were dissected into two parts, half were frozen in liquid nitrogen during sugery for RT-PCR detection and another half were kept in liquor formaldehyde for routine hematoxylin-eosin (H&E) examination and IHC detection. In 62 tumor-negative SLNs at routine H&E examination (pN0), we performed IHC and RT-PCR for KT19. Results: Of the 62 tumor-negative SLNs at routine H&E examination, 11% (7/62) were positive on extensive IHC analyses for KT-19, which were all positively identified by RT-PCR assay. Six SLNs (10%) were negative for micrometastases (with H&E and IHC for KT-19) but RT-PCR positive. There was asignificant difference in detective rate between these two methods statistically (χ2 = 4.1667 , P = 0.0412) and the coincidence were high ( kappa = 0.6483) Conclusions: As IHC analysis resulted in a 11% detection rate in H&E negative SLNs, IHC is essential to avoid false- negative SLN micrometastases. Molecular analysis with KT19 allows detection of breast cancer micrometastases with an additional 10% detection rate in H&E negative SLNs and resulted in a high coincidence with IHC analysis. However, the clinical value of these histologically negative but RT-PCR positive SLNs can only be determined with long term follow up. No significant financial relationships to disclose.