Retrospective cohort study on the safety and efficacy of panitumumab (Pmab) for patients with metastatic colorectal cancer (mCRC): The HGCSG1002 study—Analysis of clinical early predictor for the efficacy.

Abstract

593 Background: Inhibition of the EGFR pathway has become a key part in the treatment of colorectal cancer. There were few studies for clinical early predictive markers. To investigate the early magnesium (Mg2+), calcium (Ca2+), albumin (Alb), CEA and CA 19-9 plasma level reductions as a predictor for clinical outcome in terms of progression free survival (PFS) and overall survival (OS). Methods: 200 patients (pts) with mCRC treated by Pmab contained chemotherapy were retrospectively registered from 20 centers in Japan (HGCSG 1002 study). Of these, the pts that were refractory to or intolerant for 5-FU/ irinotecan/ oxaliplatin, and were never administered anti-EGFR-antibody, were included in this analysis. Mg2+, Ca2+, Alb, CEA and CA19-9 plasma levels were obtained from medical records. The differences in terms of PFS and OS according to the presence of Mg2+, Ca2+, Alb, CEA and CA19-9 reductions were evaluated by the log-rank test. Results: Of 67 pts were able to evaluate for this analysis. Pts’ characteristics were as follows: male/female 38/29, median age 64 (range 45-81), ECOG PS (0/1/2- ) 45/17/5. Response rate and disease control rate were 16.4% and 65.7%, PFS and OS were 4.3 m and 12.4 m, respectively. There were no correlations between Ca/Alb plasma level reductions and PFS/OS. Mg2+ reduction of at least 50% respect to the basal value during the course of treatment was significantly correlated with improved OS and PFS (OS, P=0.03; PFS, P=0.01), but the early reduction (until the 4th week or the 8th week after start of chemotherapy) was not correlated with OS and PFS. An early CEA serum level reduction of at least 40% until the 8th week was significantly correlated with improved OS and PFS (OS, P=0.04; PFS, P=0.07), moreover of at least 30% until the 4th week was correlated to longer PFS (P=0.053). Similar results were seen in CA19-9. Conclusions: An early CEA plasma level reduction of at least 30% or 40% was suggested to be a predictor for PFS in Pmab containing chemotherapy for mCRC pts. Although Mg2+ serum level reduction was correlated to clinical outcome, but could not show that is an early predictor for PFS and OS in our study.