ERBB2 and neoplasm: Peg et al. first reported the concept of TTL, defined as the amount of CK19 mRNA copies in all positive SLNs,25 and concluded that TTL was an independent predictor of NSLN metastasis by using multivariate analysis of tumor size, human epidermal growth factor receptor 2 (HER2), LVI, and the number of metastatic SLNs.