Journal of Cytology & Histology

Circulating Tumor Cells as Prognostic Marker in Japanese patients with Kras Wild-type Metastatic Colorectal Cancer Receiving Panitumumab after Progression on Cetuximab

Abstract

Yoshihito Ohhara, Satoshi Matsusaka, Toshiyasu Watanabe, Eiji Shinozaki, Mitsukuni Suenaga, Nobuyuki Mizunuma and Kiyohiko Hatake

Background: Panitumumab has a high affinity for epidermal growth factor receptor. Its utility as a salvage therapy is unknown in cetuximab-resistant colorectal cancer. We assessed the prognostic and predictive role of circulating tumor cells (CTCs) in KRAS wild-type metastatic Colorectal Cancer (mCRC) patients treated with panitumumab after progression on cetuximab.
Methods: Panitumumab (6 mg/kg every 2 weeks) was administered as salvage therapy in a patient with cetuximab-resistant mCRC. The CTC count in whole blood at baseline was determined using immunomagnetics.
Results: Nineteen patients were enrolled in the study between July 2010 and March 2011. Five patients had Stable Disease (SD) with a response rate of 0%. Four patients reached long-SD, which was defined as continuous SD of more than 120 days. All of these four patients had <2 CTCs. Multivariate analysis revealed that ≥2 CTCswas an independent predictor of Progression-Free Survival (PFS) (hazard ratio: 7.275, P=0.013). Patients with ≥2 CTCs had a shorter median PFS than those with <2 CTCs (1.8 versus 3.6 months, P=0.008). No statistically significant difference was observed in median overall survival between patients with ≥2 CTCs and those with <2 CTCs (3.2 versus 6.7 months, P=0.164).
Conclusions: These results suggest that <2 CTCs indicates that panitumumab may be effective in patients with KRAS-wild-type mCRC after progression on cetuximab.