Procedural data will be recorded from patients with liver metastases from colorectal cancer who have received at least one course of systemic chemotherapy and who have been assessed by an appropriately constituted MDT (or equivalent) as appropriate to receive irreversible electroporation.

Inclusion Criteria:

• Patients aged 18 years and over, able to provide informed consent and with histological confirmation of a diagnosis of colorectal cancer from primary tumour.
• Liver lesions demonstrating radiological characteristics (on magnetic resonance scan) of colorectal hepatic metastases without requirement for biopsy. In the setting of an intact liver, patients with up to four metastases ≤ 4cm in size are eligible for inclusion. In the setting of proposed resection plus ablation, up to two metastases ≤ 4cm in size. In the setting of recurrence after prior hepatectomy up to two metastases ≤ 4cm in size.
• Eastern Co-operative Oncology Group (ECOG) Score ≤ 2.
• Rockwood Frailty Score ≤ 3.
• Serum bilirubin < 30 µmol/L.
• Serum creatinine < 150 µmol/L.
• Up to two lung metastases (< 2cm in size permitted at enrolment).
• Prior treatment with at least one course of systemic chemotherapy (± biologic agent) mandated. Chemotherapy protocol is not specified and is at clinician discretion.
• Primary rectal tumour can remain in situ treated with radiotherapy/chemoradiotherapy according to tumour board recommendations. Primary colonic tumour can remain in situ.
• No prior hepatic tumour ablation

Exclusion Criteria:

• Patients involved in other research studies.
• Inability to give informed consent.
• Patients who are pregnant.
• Accepted exclusions to IRE from consensus criteria including:
• Platelet count < 50x109 U/L.
• International normalised ratio (INR) for blood clotting > 1.7.
• Prior hepatic tumour ablation.

Cardiovascular fitness related exclusions:

• History of ventricular arrhythmia.
• Implanted pacemaker or defibrillator.
• Congestive cardiac failure NYHA Class ≥ 3.

Tumour-related exclusions:

• Tumour ≥ 4 cm in size.
• Advanced multi-site metastatic cancer (any of the following): peritoneal metastases (M1c), bone metastases, > 2 lung metastases, all segment involvement multiple liver metastases.
• Jaundice (serum bilirubin > 30 µmol/L).
• MDT/tumour recommends use of thermal ablation instead of IRE for any given lesion.