Relationships between tumour response and primary tumour location, and predictors of long-term survival, in patients with RAS wild-type metastatic colorectal cancer receiving first-line panitumumab therapy: retrospective analyses of the PRIME and PEAK clinical trials

Br J Cancer. 2018 Aug;119(3):303-312. doi: 10.1038/s41416-018-0165-z. Epub 2018 Jul 17.


Background: Data from two trials of panitumumab in metastatic colorectal cancer (mCRC) were retrospectively analysed to investigate the effects of primary tumour location on early-tumour shrinkage (ETS) and depth of response (DpR), and identify factors predicting long-term survival.

Methods: Patients with RAS wild-type mCRC from PRIME (NCT00364013) and PEAK (NCT00819780) were included. ETS was defined as a ≥30% reduction in the sum-of-the-longest-diameters of measurable target lesions at eight weeks. DpR was the maximum percentage change from baseline to nadir in patients with shrinkage. Univariate and multivariate logistic analyses of short- versus long-term survivor data were performed.

Results: A total of 435/559 (78%) patients had left-sided disease. Of these, a higher proportion of patients treated with panitumumab versus comparator achieved ETS (PRIME: 62% vs. 36%; PEAK: 58% vs. 41%); median DpR was also higher with panitumumab (PRIME: 59% vs. 49%; PEAK: 70% vs. 48%). In pooled analyses of the studies, more patients with right-sided disease achieved ETS if treated with panitumumab than comparator (39% vs. 29%). Panitumumab treatment consistently predicted long-term survival.

Conclusions: First-line panitumumab was associated with improved ETS and DpR vs. comparator in patients with left-sided mCRC. ETS may identify a subgroup of patients with right-sided disease who might respond to panitumumab.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antineoplastic Combined Chemotherapy Protocols / administration & dosage*
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / pathology
  • ErbB Receptors / antagonists & inhibitors
  • ErbB Receptors / genetics
  • Female
  • Fluorouracil / administration & dosage
  • GTP Phosphohydrolases / genetics
  • Humans
  • Kaplan-Meier Estimate
  • Leucovorin / administration & dosage
  • Male
  • Membrane Proteins / genetics
  • Middle Aged
  • Neoplasm Metastasis
  • Organoplatinum Compounds / administration & dosage
  • Panitumumab / administration & dosage*
  • Progression-Free Survival
  • Proto-Oncogene Proteins B-raf / genetics
  • Proto-Oncogene Proteins p21(ras) / genetics
  • Retrospective Studies
  • Treatment Outcome


  • KRAS protein, human
  • Membrane Proteins
  • Organoplatinum Compounds
  • Panitumumab
  • EGFR protein, human
  • ErbB Receptors
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • GTP Phosphohydrolases
  • NRAS protein, human
  • Proto-Oncogene Proteins p21(ras)
  • Leucovorin
  • Fluorouracil

Supplementary concepts

  • Folfox protocol