Ultrasound-guided percutaneous MWA of liver cancer is a relatively new technique with favorable long-term outcomes.Butthe results are mainly from single center reports.A larger scale data need to be analyzed to evaluate the technique. This study is designed to investigated the efficacy of cooled-tip microwave ablation (MWA) for primary liver cancer (PLC) and analyzed the prognostic factors on a multicenter database.Between January 2013 and December 2018, all the PLC patients underwent ultrasound-guided percutaneous cooled-tip MWA as a primary treatment will be enrolled from at least ten Chinese institutions with different levels of MWA experience. All the patients will be closely followed up until June 2019. Clinicopathologic data, recurrence and survival estimates, complications and prognosis-relative factors will be measured.

Inclusion Criteria:

• absence of ascites or the depth of ascites on US detection less than 4 cm;
• a normal serum total bilirubin level or less than 60 µmol/L;
• a normal albumin level or not less than 30 g/L;
• for radical treatment, single lesion of 8 cm or smaller, three or fewer multiple lesions with a maximum diameter of 4 cm or less, absence of portal vein cancerous thrombus or extrahepatic metastases;
• for palliative treatment, those with large or multiple lesions, suffering multiple metastases and unsuitable for other modalities can be considered to undergo the MWA on the condition of good hepatic function and blood coagulation function to tolerate the procedure.

Exclusion Criteria:

Contraindications include patients who have

1. clinical evident liver failure, such as massive ascites or hepatic encephalopathy or with a trance-like state;
2. severe blood coagulation dysfunction (prothrombin time of more than 30 seconds, prothrombin activity less than 40%, and platelet count less than 30 cells×109/L);
3. high intrahepatic tumor burden (tumor volume >70% of the target liver volume or multiple tumor nodules) or high extrahepatic tumor burden;
4. acute or active inflammatory and infectious lesions at any organ;
5. acute or severe chronic renal failure, pulmonary insufficiency or heart dysfunction;
6. relative contraindication concerns medical risk for the tumor proximity to diaphragm, gastrointestinal tract, gallbladder, pancreas, hepatic hilum and major bile duct or vessels, which may require adjunctive techniques to prevent off-target heating of adjacent structures during the ablation procedure.