This is a single-arm, prospective, multicenter, study. Individuals who are assessed for microwave (MW) ablation of HCC in accordance with their institution's standard of care (SOC), who meet study entry criteria and sign the informed consent, will be enrolled. The patients will be treated with MW ablation and afterwards followed for up to 36 months after the original ablation procedure to assess efficacy and safety. In addition to the final analysis after all enrolled patients complete the 36-month observation period, a summary of selected endpoints will be provided after all enrolled patients have completed each of the 1-month and 12-month visits.

To provide sites with an opportunity to get equal experience in the use of the Certus system, there will 3 patients treated as part of a run-in phase. These patients will only be included in the safety set.

Patients who have a single HCC tumor up to 5 cm or a maximum of 3 HCC tumors of up to 3 cm per tumor will receive the same procedure: microwave ablation using only the NeuWave Certus Microwave Ablation System. Patients in this study will come to their study site for the ablation procedure. After the ablation procedure, the patient will be observed, which in most cases is expected to be 2 to 3 hours, and afterwards may return home. If the Study Doctor decides it is warranted for patient safety, the patient will remain in the hospital longer.

A minimum of one MRI of the liver must be taken at Baseline/Screening to ascertain tumor type, location, and size. (Tumor size will be measured in longest diameter and the diameter that is perpendicular to this longest diameter; tumor size must be measured with at least 2D imaging.) Physicians who are experienced with tumor ablation will do all ablations percutaneously using only the NeuWave Certus Ablation System. During the ablation, patients will be under an anesthesia method as per the institution's SOC. Ultrasound and/or CT scan will be used to guide the probe to the tumor and confirm accurate placement of the probe prior to emitting the microwaves.

Within 7 days after ablation, contrast-enhanced MRI will be done to confirm the completion of the ablation procedure. According to the standard practice at each study site, ablation confirmation will be classified as:

• complete tumor ablation with adequate margin (A0).
• complete tumor ablation with insufficient margin (A1).
• incomplete tumor ablation (A2). Over the course of 3 years, patients will return to their study site for post ablation follow-up visits, which will be carried out per the Schedule of Activities (see Table 1 at the end of the Synopsis). The follow-up schedule will be based on the original ablation procedure date. A re-ablation for any reason will not re-start or change the follow-up visit schedule.

At every follow-up visit, every patient will be scanned with at least one MRI to see if there are any tumor foci at the edge of the ablation zone, which indicates tumor progression. Repeat microwave ablation (using the Certus Microwave Ablation System only) may be performed for recurrence of target tumor(s) or to achieve complete tumor ablation with adequate margin (A0) of the target tumor(s) if the initial ablation had an insufficient margin, if the treating physician deems appropriate and necessary.

While repeat ablations for a recurrence may be conducted at any point during the study duration, repeat ablations to correct an ablative margin may only be performed within the first 30 days of the original ablation (by Visit 3).

Inclusion Criteria:

• Diagnosed primary or recurrent HCC determined in accordance with the institution's SOC procedure, a single tumor size up to 5 cm or a maximum of 3 tumors up to 3 cm per tumor. Tumor size must be measured with at least 2-dimensional (2D) imaging.
• Scheduled for microwave ablation of the liver.
• Performance status 0-2 (Eastern Cooperative Oncology Group classification).
• Functional hepatic reserve based on the Child-Pugh score (Class A or B).
• Give voluntary, written informed consent to participate in this study and willing to comply with study-related evaluation and procedure schedule.
• At least 18 years of age.

Exclusion Criteria:

1. ASA score ≥ 4.
2. Active bacterial or fungal infections which are clinically significantly.
3. Chemotherapy or radiation therapy for HCC performed within 30 days prior to the study procedure.
4. Patient with implantable pacemakers or other electronic implants.
5. Planned/ scheduled liver surgery.
6. Platelet count ≤ 50 × 109/L.
7. Patients with uncorrectable coagulopathy at time of screening based on investigator judgement. Severe blood coagulation dysfunction (bleeding tendency, prothrombin time [PT] was greater than normal control for 3~5 seconds, platelet count [PLT] was less than 50x109/L, and the international normalized ratio [INR] was greater than 1.5).
8. Patient with renal failure and on renal dialysis.
9. Scheduled concurrent procedure other than MW ablation in the liver.
10. Pregnant or breast feeding.
11. Physical or psychological condition which would impair study participation.
12. Participation in any other interventional clinical study within 1 month before screening and concurrently during the study.
13. The patient is judged unsuitable for study participation by the investigator for any other reason.

Participants who met all inclusion/exclusion criteria, were treated with the NEUWAVE microwave ablation device, and were not part of the 'run-in' phase.

36 Months

Adverse Events (AEs) were defined as any undesirable clinical occurrence in a participant, whether attributable to the study device/procedure or not. AEs were captured for the first 30 days after the ablation procedure. After 30 days, only Serious Adverse Events (SAEs) were captured throughout the duration of the study (36 months).