GCG and breast cancer: Furthermore, according to a previous report, a comparison of the NRS (Numeric Rating Scale) and plasma concentration of OXY during postoperative pain management in patients with breast cancer showed that the plasma concentration of OXY was 17.8 ± 13.5 ng/ml in NRS 0–3, 31.6 ± 20.9 ng/ml in NRS 4–6, and 50.7 ± 24.3 ng/ml in NRS 7–10.29