Correlation of outcome with early metabolic response on FDG-PET in treatment of locally advanced nasopharyngeal carcinoma

Abstract

Background: Skull base changes often persist on CT and MRI after treatment in locally advanced nasopharyngeal carcinoma (NPC) and cannot be differentiated from active tumor. We prospectively evaluated the metabolic response of T3/T4 NPC during treatment with PET scans. Early metabolic response was correlated with outcome after treatment. Methods: 50 patients with T3/T4, N0-3, M0 NPC were recruited. All patients had 3 cycles of induction chemotherapy (IC, physician’s choice of regime) before concurrent chemoradiation (CRT) with cisplatin 100mg/sqm for 3 cycles. PET scans were performed before and after IC and at 30Gy of CRT. For primary tumor that showed complete metabolic response (mCR, defined as SUV max in tumor ≤1.25x liver background activity) on reassessment PET, the dose to tumor stopped at 70Gy. For those who did not achieve mCR, a boost dose was given to the residual tumor to total 76Gy. Results: On post-IC PET scan, 2 patients with extensive intracranial disease showed no response with static and progressive disease respectively and did not proceed to CRT. 48 patients showed regression of tumor and decreased metabolic activity on post-IC PET, 16 of whom achieved mCR. One patient with mCR after IC refused CRT. 47 patients proceeded to CRT. 44 patients had reassessment PET at around 30Gy and 25 patients had mCR during CRT. 47 patients who completed CRT were included in survival analysis. Median follow up after completion of CRT was 28 months. Among the 15 cases who achieved mCR after IC, all patients were disease free without relapse at time of analysis. Among the 32 patients who did not achieve mCR after IC, there was 1 persistent loco-regional disease, 1 local and 1 regional relapse and 6 developed distant metastases. The 3 year NP control, regional control, distant metastases free, progression free survival and overall survival were 89.4%, 96.9%, 79.5%, 49.2% and 81% respectively compared with 100% corresponding survival rates among patients who achieved mCR after IC. The difference in progression-free survival was statistically significant (p = 0.045) Conclusions: Early mCR was observed in 32% patient after IC and 56.8% of patients during CRT. mCR after IC predicts for very favourable outcome.