Objective assessment of sentinel node tumor burden and its impact on sentinel node localisation in breast cancer

Abstract

605 Background: Extensive tumor infiltration of the draining lymph nodes may prevent the migration of tracer to the sentinel node(SN), adversely affecting SN identification. Methods: A total of 202 breast cancer patients underwent SN biopsy using 99mTc albumin colloid and Patent Blue V injected peritumorally. This was followed by standard axillary clearance in all patients at the same operation. Tumor burden in the SN was assessed by measuring the size of metastasis, percentage replacement(PR) of the SN by tumor and by documenting extranodal invasion(EI). Digital images of the marked slides were acquired and measurements were made using Image Pro Plus software. Results: The overall SN identification rate was 94.6% (191/202), of which 5 were false negatives. Only 18% (2/11) of patients with failed SNB had evidence of nodal metastases on completion axillary clearance. A total of 83 positive SNs were removed from 64 patients. Radioisotope count in the SNs decreased with increasing PR of the SNs by tumor (p=0.005). 30% (24) of the nodes removed were not hot (counts<10 times the background count). The mean PR by tumor of these nodes was 55% (SD 36) as compared to 33% (SD 33) for hot nodes (p=0.009). 20% (16/81) of the positive SNs showed EI. 69% (11) of nodes with EI were not hot (radioisotope count ratio <10) and would not be localised if the radioisotope was used alone. SNs with EI had a lower radioisotope count compared to SNs without EI (p<0.0001). The mean PR by tumor of nodes with EI was 70% (SD 26) compared to 32% (SD 33) of nodes without EI. This shows that extranodal growth of the tumor would occur once the node is >50% replaced with tumor. There was no correlation between radioisotope uptake and size of metastasis in the SN. There was no correlation between blue dye uptake and tumor burden in the positive SN. Conclusion: In an individual SN, the PR by tumor and EI are markers of lymphatic obstruction and significantly associated with reduced radioisotope uptake. These results suggest that >50% replacement of the node by tumor will compromise the lymphatic flow and may lead to failed localisation of the node if the radioisotope is used alone. However, the SN tumor burden does not affect blue dye uptake. This result provides an argument for using a combination of blue dye and radioisotope for SN biopsy. No significant financial relationships to disclose.