4. Diagnostic value of SLNB
Among the 325 patients, 46 (12.13%) had 133 metastatic lymph nodes. A
total of 44 patients had SLN metastases, thereby accounting for 95.65%
of metastatic cases. Of the 325 patients in whom SLNs were successfully
identified, 26 patients had SLN metastasis and PLN metastasis, 18
patients had SLN metastasis but no PLN metastasis (including two
patients with micro-metastasis in SLNs), two patients had only PLN
metastasis and no SLN metastasis, and 279 patients had no metastasis in
the SLNs and PLNs. As a result, the sensitivity of SLNB when used to
identify nodal metastatic disease was 92.86%. Among the 281 patients
with negative SLN results, 279 had true-negative non-SLNs, which
resulted in a negative predictive value (NPV) of 99.29%. Two patients
had negative SLNs but positive non-SLNs, yielding a false-negative rate
(FNR) of 7.14% (Table 2). The common characteristics of the two
false-negative cases were tumour diameter larger than 20 mm and the
presence of DSI and LVSI (Table S3, Figure 1D). We analysed the subgroup
of patients with tumours smaller than 20 mm (267 cases) and obtained an
ideal FNR of 0% and higher DR (97.75%), sensitivity (100%), and NPV
(100%). Compared to the ≥20-mm-tumour-size subgroup, the specificity,
NPV, and accuracy were markedly improved (Table S4). Furthermore,
we found that lymph node metastatic
status was significantly associated with tumour size (p = 0.000), depth
of stromal invasion (p = 0.028), LVSI (p = 0.000) and stage (p = 0.000),
and multivariate analysis showed that tumour size, stage, and LVSI are
independent risk factors for lymph node metastasis (Tables S5 and S6).