Although axillary lymph node dissection (ALND) is conventionally indicated for metastasis in the sentinel lymph node (SLN), the omission of ALND is being discussed more often in recent years. However, because of the lack of specific guidelines, it is unclear which cases should be treated without ALND. In this study, we performed one-step nucleic acid amplification of the SLN with metastasis to determine the total tumor load (TTL), that is, the number of cytokeratin (CK) 19 mRNA copies. After ultrasonography (US) of ALN, the ultrasonographic findings were combined with TTL to rate SLN metastasis. In the rating, a total score was obtained by assigning 1 point each for (a) TTL of ≥15000 copies/μL, (b) US findings of a long-to-short LN diameter ratio of ≤2, and (c) US findings of no echogenic hilus. We then investigated the association between the total score and metastasis in the non-SLN. Results showed that while 87.5% (5/6) of patients with positive non-SLN scored ≥2 points, only 3.1% (1/34) of patients with negative non-SLN did so, suggesting that a total copy number of CK19 mRNA, US findings of a long-to-short LN diameter ratio, and the presence/absence of echogenic hilus are important predictors for non-SLN metastasis. This novel scoring system is expected to help determine which patients need ALND or what postoperative therapy is necessary.