A validation study of a new molecular diagnostic assay: The Dartmouth-Hitchcock Medical Center experience with the GeneSearch™ BLN assay in breast sentinel lymph nodes

BackgroundSentinel lymph node (SLN) processing remains variable in terms of performing multiple tissue levels and immunohistochemical (IHC) or PCR-based assays. A rapid and reliable molecular pathology assay, as an adjunct to routine SLN processing, could minimize and standardize the histologic evaluation needed for an accurate and clinically significant diagnosis. We compared the recently FDA-approved Veridex GeneSearch™ Breast Lymph Node (BLN) Assay (Veridex, LLC; Warren, NJ), a real time reverse transcriptase-polymerase chain reaction assay that is designed to detect metastases > 0.2 mm, with our standard lymph node processing.Materials and methodsThe GeneSearch™ BLN assay evaluates RNA expression data for three target genes (mammaglobin, cytokeratin 19, and internal control porphobilinogen deaminase), and provides a qualitative (positive/negative) result. In 59 patients, the assay was performed on SLN tissue that would normally be deep within the tissue block and not routinely evaluated histologically. Two 1 -mm slices from the outer node portions were submitted fresh for RNA extraction; the remaining tissue was submitted for routine histology.ResultsOf the 59 patients, the assay determined 43 as true negative, eight as true positive, one as false-negative, three as false-positive, and four as invalid. Assay sensitivity was 88.9%, specificity 93.5%.DiscussionThe sensitivity of the assay sampling from the outer node tissue was high (88.9%) and identical to that validated in the large registration study in which half of the node was assessed as alternate slices (87.6%). Our protocol uses this assay as an adjunct to traditional histologic evaluation, to reduce and standardize the number of tissue sections needed for thorough SLN evaluation, and to enhance our ability to bank RNA.