CETUXIMAB PREDICTIVE FACTORS

Clin Cancer Res. 2013 Nov 11. [Epub ahead of print]

PIK3CA, BRAF and PTEN status and benefit from cetuximab in the treatment of advanced colorectal cancer - results from NCIC CTG / AGITG CO.17.

Karapetis CS, Jonker D, Daneshmand M, Hanson JE, O'Callaghan CJ, Marginean EC, Zalcberg JR, Simes J, Moore MJ, Tebbutt N, Price TJ, Shapiro JD,Pavlakis N, Gibbs P, Hazel GV, Lee U, Haq R, Virk S, Tu D, Lorimer IA.

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Abstract

PURPOSE:

Cetuximab improves survival in patients with K-ras wild-type advanced colorectal cancer (CRC). We examined the predictive and prognostic significance of additional biomarkers in this setting, in particular BRAF, PIK3CA and PTEN.

EXPERIMENTAL DESIGN:

Available colorectal tumor samples were analyzed from the CO.17 study. BRAF mutations were identified in tumor-derived DNA by direct sequencing and PIK3CA mutations were identified using a high resolution melting screen with confirmation by sequencing. PTEN expression by immunohistochemistry (IHC) was performed on tissue microarrays. For each biomarker, prognostic and predictive effects were examined using a Cox model with tests for treatment-biomarker interaction.

RESULTS:

572 patients with pre-treated CRC were randomly assigned to receive cetuximab or best supportive care (BSC). Of 401 patients assessed for BRAF status, 13(3.2%) had mutations. Of 407 patients assessed for PIK3CA status, 61(15%) had mutations. Of 205 patients assessed for PTEN, 148(72%) were negative for IHC expression. None of BRAF, PIK3CA or PTEN was prognostic for overall or progression-free survival in the BSC arm. None was predictive of benefit from cetuximab, either in the whole study population or the K-ras wild-type subset. In the K-ras wild-type subgroup, the overall survival adjusted HR according to BRAF mutation status was 1.39 (interaction p=0.69), PIK3CA mutation status HR 0.79, (interaction p = 0.63), and PTEN expression HR 0.75 (interaction p= 0.61).

CONCLUSIONS:

In chemotherapy-refractory CRC, neither PIK3CA mutation status nor PTEN expression were prognostic, nor were they predictive of benefit from cetuximab. Evaluation of predictive significance of BRAF mutations requires a larger sample size.