Tumor reduction in pancreatic versus metastatic sites in a randomized phase III study (MPACT) of weekly nab-paclitaxel (nab-P) plus gemcitabine (Gem) versus Gem alone.

Abstract

382 Background: nab-P + Gem was superior to Gem alone in MPACT, a phase III metastatic pancreatic cancer (PC) trial, for all endpoints examined. An updated analysis verified the superior overall survival of nab-P + Gem vs Gem alone (median 8.7 vs 6.6 months; hazard ratio 0.72; P < 0.001). Whether antitumor agents may have differential activity on pancreatic vs metastatic lesions in PC has not been definitively addressed. This prespecified analysis examined the activity of nab-P + Gem vs Gem alone in reducing tumor size in pancreatic and metastatic lesions. Methods: Previously untreated metastatic PC pts (N = 861) were randomized 1:1 to receive nab-P 125 mg/m2 + Gem 1000 mg/m2 days 1, 8, and 15 every 4 weeks or Gem alone 1000 mg/m2weekly for 7 weeks followed by 1 week of rest (cycle 1) and then days 1, 8, and 15 every 4 weeks (cycles ≥ 2). Most pts (99%) underwent spiral CT imaging, allowing precise tumor measurement. Changes in the sum of target tumor diameter from baseline to postbaseline nadir were evaluated separately for pancreatic and metastatic lesions by independent radiological review. Results: Baseline sizes of pancreatic and metastatic tumors were comparable between treatment arms (Table). nab-P + Gem elicited an approximately 3-fold greater median percentage decrease vs Gem alone in pancreatic (−22.15% vs −7.02%) and metastatic (−24.27% vs −8.74%) tumor size, agreeing with the 3-fold higher overall response rate of target lesions by RECIST. Tumor shrinkage was similar between pancreatic and metastatic lesions. Conclusions: nab-P + Gem was associated with a greater reduction in tumor size of both primary and metastatic lesions compared with Gem alone. Clinical trial information: NCT00844649. [Table: see text]