Purpose: The sentinel lymph node (SLN) biopsy represents a new standard method for axillary staging in patients with breast cancer. Although the radioisotope technique has been used to identify SLN, no standard for radioisotope success has been defined. In this study, we intended to define the thrashold level of radioactivity which could predict all cases of positive SLN.
Methods: SLN biopsy was performed in 86 patients with clinical stage T1-2, N0 breast cancer, using both isotope (^(99m)Tc-ASC or ^(99m)Tc-HSA) and blue dye. All lymph nodes having higher isotope counts than the background were sampled. The nodes with the three highest radioactivities were identified as S1, S2 and S3 and the predictive value of metastatic SLN was analyzed according to the level of SLN-to-background ratio.
Results: SLN was successfully identified in 100% of the 86 patients, with 10.5% (9/86) of SLN identified by isotope alone and 1.2% (1/86) by blue dye alone. Metastasis of axillary lymph node was documented in 35 of 86 (40.7%) and the false negative rate of SLN metastasis was 8.6% (3/35). In 33 SLN metastatic cases, the node with the highest count (S1) contained metastasis in 29 (87.8%), but in 4 (12.2%) it was benign. The sensitivity of metastatic SLN was 91.4% (32/35) when only S1, S2 and S3 were biopsied. Although three patients had metastasis in S3, there were concurrent metastases in S1 or S2. Metastatic rates according to SLN-to-background ratios, of 1~4, 5~9, 10~20, 21~50, and >50 were 5/43 (11.6%), 8/43 (18.6%), 8/43 (18.6%), 7/43 (16.3%) and 15/43 (34.9%) respectively and there was no statistical significance (P=0.261). However, SLN with higher radioactivity had a higher metastatic rate (P=0.004).
Conclusion: There was no optimal SLN-to-background ratio capable of identifying positive SLN in all cases but SLN with higher radioactivity had a higher metastatic rate. To reduce false negative rate, SLN biopsy requires the removal of all nodes higher than background regardless of the relative magnitude of counts and requires using both radioisotope and blue dye and the removal of all clinically suspicious non-SLN.
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