The chemotherapy monitoring is currently based on radiological (RECIST 1.1 guideline) and clinical evaluation every 3 months. Circulating markers as Carcino Embryonic Antigen (CEA), circulating tumour DNA and total cell free DNA represent an alternative approach to evaluate the response. In the field of metastatic colorectal cancer (mCRC) recent studies suggest that early evaluation could be clinically relevant. Indeed, early tumoral response seems to be correlated to overall survival. Moreover, post-operative morbidity increases with the number of prior chemotherapy treatments. Early evaluation could allow to modify chemotherapy regimens when response appears to be insufficient.

The aim of the present study is to evaluate, in a prospective cohort of patients treated with systemic IV chemotherapy (5 Fluorouracil +/- oxaliplatin +/- irinotecan) +/- targeted therapy as first line treatment for a mCRC, the correlation between early variations of circulating tumour markers including CEA, circulating tumour DNA and total cell free DNA, and the 3 months objective response as defined in the RECIST 1.1 guideline.

Inclusion Criteria:

• Male or female, age superior to 18 years.
• Histologically confirmed metastatic colorectal adenocarcinoma.
• Measurable disease according to the RECIST 1.1 guideline
• ECOG performance status <3.
• Disease requiring IV chemotherapy (5 Fluorouracil +/- oxaliplatin +/- irinotecan) +/- targeted therapy (cetuximab or panitumumab or bevacizumab) every 14 days
• No prior chemotherapy for this adenocarcinoma with the exception of adjuvant chemotherapy
• Signed and dated informed consent document.

Exclusion Criteria:

• Medical history of cancer within 5 years
• Medical contraindication for a treatment consisted of IV chemotherapy (5 Fluorouracil +/- oxaliplatin +/- irinotecan) +/- targeted therapy (cetuximab or panitumumab or bevacizumab)
• Patient with known psychiatric or substance abuse disorders that could interfere with cooperation with the requirements of the study