PTN and breast cancer: Breast cancer patients with plasma PTN concentrations above the detectable level (1 ng/ml) were considered “PTN high” whereas others were considered “PTN low.” Interestingly, even though PTN concentration did not significantly differ between stage IV, lymph node–positive (LN+), and lymph node–negative (LN−) patients (Fig. S1 D), the PTN-high cohort of patients had a worse overall survival than PTN-low patients (Fig. 1 I).