Patients

This retrospective study was performed on a cohort of 1205 consecutive patients who were newly diagnosed with stage I to IV NPC at Sun Yat-sen University Cancer Center (SYSUCC) from June 1, 2006 to December 31, 2010. This study was reviewed and approved by the Medical Ethics Committee of SYSUCC.

Patient data were retrieved from the archived patient medical records and survival data were provided by the department that performed the follow-up examinations. The collected data included age, sex, smoking status, TNM stage, histological type, treatment, time of diagnosis, time of recurrence and metastasis, and pretreatment CysC level. We adopted the seventh edition of the AJCC/UICC staging system for classification of NPC.

Potentially eligible patients had been pathologically confirmed to suffer from NPC. They also had to have received comprehensive pretreatment evaluations, including physical examinations, routine hematological and biochemical examinations, computed tomography or magnetic resonance imaging of the head and neck, chest X-ray, abdominal ultrasonography and emission computed tomography of the bone.

As the serum CysC level is regulated by renal function, we excluded those patients with abnormal renal function (GFR ≤60 ml/min/1.73 m² as estimated using the Modification of Diet in Renal Disease [MDRD] formula) ¹⁸. Patients were also excluded if they had prior malignancies, previous anticancer therapy, or insufficient biochemical test results or survival data.

All patients were treated with standard curative radiotherapy with or without chemotherapy (radiation dose: 60-72 Gy for the nasopharyngeal region, 50-66 Gy for the regional lymph nodes). Most patients (79.5%) classified as stage III-IV and a minority of patients (30%) classified as stage II received a platinum-based chemotherapy regimen.