Of these SNs, 10 were diagnosed as metastasis positive by OSNA and confirmed by ddPCR to have <i>PIK3CA</i> mutations, with no false negatives.<h4>Conclusions</h4>Assessment of tumor-derived mutated DNA in SNs may be a useful technique to detect SN metastasis, as confirmed by ddPCR analysis. This evidence concerns the gene PIK3CA and neoplasm.