Inclusion Criteria:

- Male or female ≥ 18 years old

- Histologically confirmed diagnosis of colorectal cancer

- Asymptomatic or resected primary tumor

- Metastatic colorectal cancer patient not eligible for curative surgery

- At least one target lesion:

- Unidimensionally measurable on cross-sectional imaging

- In an area not previously irradiated

- Disease progression after failure of active drugs (5-Fu or 5-Fu prodrugs, irinotecan,
oxaliplatin, bevacizumab)

- Patients with bone metastases are eligible if they have other measurable lesions

- WHO performance status ≤ 2

- Confirmation of KRAS mutation in codons 12 or 13 in the primary tumor or metastases

- Total bilirubin ≤ 1.5 ULN, ALT or AST ≤ 2.5 ULN (or < 5 in case of liver impairment)

- Haemoglobin ≥ 10 g/dL, neutrophils ≥ 1,500/mm3, platelets ≥ 100,000/mm3

- Serum creatinine ≤ 1.5 ULN

- Negative pregnancy test in women of childbearing potential

- Use of an effective contraceptive method during the whole treatment and up to 3
months after the completion of treatment in males and females

- Life expectancy of at least 3 months

- Informed consent signed prior any study specific procedures

- Tumor evaluation should be performed within 3 weeks prior to starting treatment

Exclusion Criteria:

- History of Gilbert's syndrome

- Symptomatic brain metastases or carcinomatous meningitis

- Bone-only metastases

- History or presence of other cancers within the past 5 years (except curatively
treated non-melanoma skin cancer and in situ cervical cancer)

- Prior surgery or radiotherapy within 4 weeks before entering the study

- Cardiac arrhythmia requiring treatment (except for beta-blockers and digoxin),
unstable cardiac disease, myocardial infarction within the previous 6 months, > grade
II NYHA heart failure, uncontrolled hypertension

- Kalemia lower than normal serum potassium value

- From ECG, QTc interval > 470 ms

- History of acute or chronic pancreatitis

- History of epileptic seizures requiring long-term anticonvulsant therapy

- History of organ transplantation with use of immunosuppression therapy

- Severe bacterial or fungal infection (Grade > 2 NCI-CTCAE v.4.0)

- Known HIV infection

- Long-term use of CYP 3A4 enzyme-inducing agents such as rifampicin, St. John's Wort
(hypericum perforatum), phenytoin, carbamazepine, phenobarbital, dexamethasone, and
ketoconazole

- Pregnant or breastfeeding women

- Bowel malabsorption or extended bowel resection that could affect the absorption of
sorafenib, occlusive syndrome, inability to take oral medications

- Inflammatory bowel disease with chronic diarrhea (NCI-CTCAE v.4.0)

- Participation in another clinical trial 30 days prior to study entry

- Concurrent treatment with any other investigational product or anticancer therapy
(except for irinotecan or sorafenib)

- Psychological, social, geographical disorders or any other condition that would
preclude study compliance (treatment administration and study follow-up).