Use of quantitative RT-PCR assay to predict metastases size of sentinel node from breast cancer patients

Abstract

621 Background: A RT-PCR Assay (GeneSearch, Veridex, LLC), FDA approved and CE marked to detect metastases > 0.2 mm in sentinel lymph nodes (SLNs) of breast cancer patients, has been in clinical use in our institute for 25 months. The assay gives qualitative (negative/positive) results by applying cutoff values to cycle times (Cts) of mammaglobin (MG) and cytokeratin 19 (CK19) (cutoff values = 30 / 31 Cts). This study evaluates if quantitative Ct values can be used to estimate the probable size of nodal metastases. Methods: To date 384 patients have been clinically tested with the BLN Assay at Institut Jules Bordet. An additional 74 patients were tested in a pilot study. Both sets had SLNs of breast cancer patients divided in ∼2 mm pieces. Alternating pieces were homogenized and intra-operatively processed by the assay. The remaining pieces were used for histological analysis (positive when > 0.2 mm). During clinical use, same-surgery complete axillary dissection was performed when the assay was positive (n=59). Results: Performance of the assay's qualitative results against permanent section H&E was similar for both groups (total N = 458), for a total sensitivity 89% (68/76), specificity 95% (364/382) and overall agreement 94%. The marker Ct values are correlated with metastases size as determined by H&E on adjacent node pieces (r = -0.74 for MG and -0.77 for CK19, p < 0.001). Lower Ct values indicate increased likelihood of macrometastases reported by H&E, as described in the table. Additionally, Assay Ct values in the SLN were predictive of metastases in non-SLN nodes. For example when CK19 and MG < 24 Cts, the non-SLN positivity rate jumps from 29% to 58%. Conclusions: The BLN Assay's high intra- operative qualitative performance minimizes the need for second surgeries for complete axillary dissections. Results from this investigational study examining the marker Ct values suggest that the assay may provide valuable individual tumor volume data intra- operatively or post-operatively. [Table: see text] [Table: see text]