Analysis of metabolic response (MR) by positron emission tomography (PET) compared with tumor response by computed tomography (CT) from MPACT, a phase III trial comparing nab-paclitaxel (nab-P) plus gemcitabine (G) versus G alone for patients (pts) with metastatic adenocarcinoma of the pancreas.

Abstract

254^ Background: In the MPACT trial, nab-P + G demonstrated superior efficacy vs G alone for the treatment of metastatic pancreatic cancer (PC). Pts with an MR (according to EORTC criteria) had a 5-month improvement in median overall survival (OS) vs those without an MR (13 vs 8 months for nab-P + G and 12 vs 7 months for G alone). This analysis examines the relationship between MR by PET and tumor response by CT. Methods: Previously untreated pts (N = 861) with metastatic PC were randomized 1:1 to receive nab-P 125 mg/m2 + G 1000 mg/m2 on days 1, 8, and 15 every 4 wk or G alone 1000 mg/m2 weekly for 7 wk followed by 1 wk of rest (cycle 1) and then days 1, 8, and 15 every 4 wk (cycle ≥ 2). Tumor responses were evaluated every 8 wk by CT using RECIST v1.0. CT-documented disease progression led to treatment discontinuation. PET scans were evaluated at baseline, wk 8, and wk 16. Results: In 257 pts with a PET scan at baseline, 252 (98%) had ≥ 2 PET-avid lesions. The rate of MR (complete [CMR] or partial [PMR]) was higher for nab-P + G vs G alone (63% vs 38%; P < 0.0001). The ORRs by CT (complete response + partial response [CR/PR]) in the same pts were 31% for nab-P + G vs 11% for G. In a pooled-treatment-arm analysis (n = 255), 130 pts (51%) had an MR by PET, and 54 (21%) had a CR or PR by CT. Among pts with an MR by PET, 32% had a CR or PR, 43% had stable disease, and 16% had progressive disease (PD) by CT. Pts who had an MR by PET in the absence of a CR or PR by CT (n = 88) had a median OS of 10 months (table). Conclusions: Rates of MR by PET in this trial were > 2-fold the response rates by CT, suggesting that PET may be a more sensitive marker of tumor response. Of the pts without a CR or PR by CT, those with an MR by PET had a longer median OS vs those without one. A set of pts who had PD by CT exhibited an MR by PET. Thus, PET may identify a set of pts who may benefit from continued treatment despite PD by CT. Further research is needed to explore the radiological and clinical characteristics of these pts. Clinical trial information: NCT00844649. [Table: see text]