RT–PCR technique for the intra-operative assessment of breast sentinel lymph nodes – Is this the way forward?

Abstract

Background

Sentinel lymph node biopsy (SLNB) is the current standard of care for lymphatic staging in early breast cancer patients. The combination of a SLNB with an intra-operative diagnosis of the SLNB enables a single staged procedure, avoiding a delayed axillary lymph node dissection (ALND) in node positive patients. The current conventional pathological techniques are resource intensive, require expert personnel and are not routinely used in many breast units.

Methods

GeneSearch™ BLN assay is a RT-PCR technique calibrated to detect SLN metastases of >0.2mm. It is designed to detect 2 clinically validated genes Mammaglobin (MG) and Cytokeratin – 19 to provide a rapid diagnosis.The SLN identification was by the combined technique using radiocolloid and patent blue dye. The excised SLNs were sliced in their short axis at intervals of 1.5 mm to 2 mm. The sections were numbered and alternate sections were processed for histopathology and RT-PCR assay.The study was conducted in 2 phases. The first phase was to evaluate the accuracy and feasibility of RT-PCR assay as an intra-operative diagnostic test. The second phase was the real time application of the results to inform decision regarding immediate ALND.

Results

This prospective study comprised of 166 patients with 164 females and 2 male patients. 86 patients had left breast cancer, 75 patients had right breast cancer and 5 patients had synchronous bilateral breast cancers. A total of 171 SLNB procedures were done and 271 SLNs were excised at an average of 1.58 SLNs per procedure. Only a total of 266 SLNs were included in the analysis as the RT-PCR assay results of 5 SLNs were invalid. All the SLNs underwent RT-PCR assay and the results were compared to the final histology. The results were recorded on per patient and per node basis. The initial validation phase of the study included 53 patients and the RT-PCR assay was performed on 92 SLNs from these patients. The sensitivity and specificity on a per patient basis was 100% and 87.1% respectively. On a per node basis, the sensitivity and specificity was 93.7% and 92.1% respectively. The average processing time for 1 SLN during this phase was 31.6 min and 47.4 min for 2 SLNs.

During the 2nd phase of the study, the actioning phase, 113 patients were recruited analysing 174 SLNs from these patients. The sensitivity and specificity of the RT-PCR assay on a per patient basis was 92.3% and 94.3% respectively. On a per node basis, the sensitivity and specificity was 94.1% and 96.4% respectively. The turn around time was significantly better at 21.5 min for 1 SLN and 32.6 min for 2 SLNs. Combining both phases, the sensitivity and specificity on a per patient basis was 95% and 92% respectively. The sensitivity and specificity on a per node basis was 94% and 94.9% respectively.

Conclusions

RT-PCR assay is a reliable intra-operative diagnostic technique for the detection of clinically relevant breast SLN metastases. It is a good alternative to conventional histopathological tests with better sensitivity but comparably less specificity.