ERBB2 and breast carcinoma: We observed that the median sTK1 level of patients with detectable sTK1 at diagnosis was comparably higher than in a study on patients with clinical stage II HER2-negative breast cancer patients using the same assay [16], but lower compared to patients with advanced breast cancer [17], suggesting that sTK1 possibly reflects tumor burden, notwithstanding the difficulties of comparing different studies.