In patients with primary liver cancer arising from the liver cells, several treatment options are available according to the stage of the disease. Thermal ablation is a treatment modality using the deposition of thermal energy via an ablation probe to locally destroy the tumor tissue. It has been accepted as being equally effective as surgical resection in patients with very small tumors, as well as for patients with more advanced disease who are not surgical candidates or who are awaiting liver transplantation. Treatment success of thermal ablation is linked to the completeness of the tumor ablation and thus to the precision with which the ablation probes can be placed within the tumors. In recent years, novel computer-assister technology has been introduced to augment accuracy in ablation probe positioning, and first reports describing the safety and efficiency of these procedures have been described in the literature. However, very few works describe the oncological outcomes of patients when using this technology for thermal ablation. In this study, the investigators aim to describe local tumor control and the oncological follow-up of patients when using computer-assisted technology for thermal ablation of liver cancer.

Curative treatment options for patients with early-stage hepatocellular carcinoma (HCC) include surgical resection, liver transplantation and local ablation. While only 20-25% of patients with HCC qualify for surgical resection or liver transplantation, local thermal ablation using radiofrequency or microwave energy represents a more tissue-sparing therapy with promising results. Thermal ablation has been accepted as valid alternative to resection in patients with very small solitary tumors (BCLC stage 0) with equally good survival rates up to 75 % at 5 years. It further represents a valid treatment modality for patients with limited tumor burden (BCLC stage A) who are not surgical candidates due to associated comorbidities. More recently, indications for thermal ablation have also been widened for patients with more advanced disease but still limited tumor burden (BCLC stage B1), as well as for use within combined treatment strategies and as bridging therapy in patients awaiting liver transplantation.

The major advantage of thermal ablation lies in its tissue-sparing yet locally destructive therapeutic character, which when combined with a minimally invasive access leads to low treatment-associated tissue trauma and morbidity. Regarding treatment efficiency, initial complete response is an independent predictive factor for survival for HCC patients treated with ablation. Hence, the precision of ablative therapy is crucial for treatment success, and relies directly on the accuracy of ablation probes positioning within the tumor target. To address this issue, advanced image-guided navigation technology has been introduced for use in liver-directed therapies. While first works reporting on the safety and accuracy of stereotactic percutaneous image-guided ablation of liver tumors are available, only few studies reporting on the oncological outcomes in liver tumors exist. No data on the oncological follow-up after stereotactic image-guided ablation of HCC is available to date, leaving the understanding of the clinical impact when using such novel navigation technology for ablative treatment in these patients scarce.

Overall, the investigators hypothesize that stereotactic image-guided microwave ablation allows a more precise and thus effective ablative treatment of HCC when compared to using conventional image-guidance techniques. This is due to the possibility of i) planning of targeting trajectories even for difficult-to-target lesions, ii) placement of ablation probes in multiple parallel needle configurations for larger lesions, iii) immediate intraoperative knowledge of treatment success through overlapping of pre- and post-ablation images with the possibility of re-ablation, and iv) reproducibility and standardization of the treatment technique. In this first retrospective analysis, the investigators aim to report therapeutic efficacy in terms local tumor control and short-term survival when using stereotactic image-guided microwave ablation for treatment of HCC, and further report procedural efficiency in terms of targeting accuracy and required time consumption.

Inclusion Criteria:

• All patients who underwent stereotactic percutaneous image-guided microwave ablation of hepatocellular carcinoma from 01.01.2015 to 31.12.2017 at Inselspital University Hospital of Bern Switzerland

Exclusion Criteria:

• Lack of general consent for data usage

Patients with hepatocellular carcinoma deemed amenable to percutaneous microwave ablation at the Multi-Disciplinary Team conference of the Department of Visceral Surgery and Medicine of the University Hospital of Bern, Switzerland