Image-Guided Ablation of Liver Tumors

Image-Guided Ablation for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) can be ablated for local control in a patient who is unsuitable for hepatic resection or transplantation. HCC can be ablated to prolong the period a patient is suitable for liver transplantation by fulfilling the Milan criteria or UCSF criteria. The Milan criteria suggest that patients with a single HCC less than 5 cm or with up to three HCCs all less than 3 cm in diameter have a better outcome after liver transplantation. The UCSF criteria suggest that patients with a single tumor 6.5 cm or smaller, maximum of three tumors with none greater than 4.5 cm, cumulative tumor size 8 cm or less have a better outcome after liver transplantation.

Results of ablation are dependent on tumor size and to a lesser extent on degree of encapsulation. Local control for HCC less than 3 cm, 3-5 cm, and 5.1-9 cm has been reported as 90%, 71%, and 45%, respectively, after RFA. The upper limit of HCC size suitable for ablation varies among institutions and is not standardized. In general, HCCs less than 5 cm are suitable for RFA, although tumors up to 7 cm have been ablated. For multiple tumors, likewise the number of tumors is necessarily limited. Again, no standardized guidelines exist. Some centers ablate up to three tumors while others ablate up to five tumors depending on size, location, and approach.

A randomized controlled trial comparing the effectiveness of RFA and surgical resection as an initial treatment for patients with small HCC found the 1-, 2-, and 3-year local disease control rates were 89%, 82%, and 75%, respectively, in the resection group and 91%, 81%, and 76%, respectively, in the RFA group. The 1-, 2-, and 3-year survival rates were not significantly different at 93%, 85.69%, and 67.26%, respectively, in the resection group and 93%, 82%, and 65%, respectively, in the RFA group.

A further nonrandomized study confirmed survival at 4 years after RFA is equivalent with surgical resection for HCCs of 5 cm or less (96%, 82%, 71%, and 68% at 1, 2, 3, and 4 years).

For RFA as salvage therapy for recurrent HCC that has been previously resected, the 5-year survival rate after RFA of solitary intrahepatic recurrence of HCC is increased when compared with no therapy.

With ethanol ablation, 2-year local recurrence rates among HCCs treated with ethanol instillation with diameters of 2 cm or less, 2-3 cm, and more than 3 cm were 10%, 18%, and 30%, respectively. Elevated baseline α-fetoprotein level, multiple HCCs, and a tumor size larger than 3 cm are predictive of recurrence when using ethanol ablation.

One randomized study comparing ethanol ablation with surgical resection found that alcohol ablation was as effective as surgical resection in the treatment of solitary (≤5 cm) and small HCC. Three-year survival rates of 60%-70% and 5-year survival rates of 30%-50% have been reported. RFA achieves therapeutic efficacy in fewer sessions than ethanol instillation and for this reason has become the preferred ablation modality. The addition of alcohol ablation after RFA improves local control significantly in HCC greater than 3 cm in diameter. A randomized control trial of RFA and microwave had equivalent therapeutic effects, complication rates, and rates of residual foci of untreated disease. However, RF tumor ablation can be achieved with fewer sessions. Survival rates at 1, 2, and 3 years were 96%, 83%, and 73%, respectively, after microwave ablation.

Microwave ablation has theoretical advantages in comparison to other thermal ablation therapies. The microwave ablation zone may be less affected by proximity to large hepatic vessels.

There is sparse published data as to the rate of local control and long-term survival after cryotherapy and ultrasound ablation. Electroporation remains an experimental technique.

Image-Guided Ablation for Hepatic Colorectal Carcinoma Metastasis

Colorectal carcinoma (CRC) metastasis can be ablated for local control in a patient who is unsuitable for hepatic resection or to make a patient suitable for resection. Hepatic resection in those who are suitable is still the gold standard treatment for hepatic colorectal metastasis.

Local control is achieved in 63%-65% of patients after RFA of CRC metastases but this varies with tumor size. Metastases 3-4 cm or less are more likely than larger tumors to result in a favorable outcome, with local control achieved in up to 98% of small tumors.

Survival data following percutaneous RFA of CRC metastases are not as good as for patients who undergo resection. Reports of cohorts not suitable for surgical resection have shown that survival in those who receive RFA exceeds the historical survival rates with no therapy. Moreover, patients who undergo RFA alone or RFA and resection show better survival than those on chemotherapy alone. Reported ranges of survival after RFA at 1, 3, and 5 years are 91%-93%, 28%-69%, and 25%-46%, respectively.

Magnetic resonance imaging (MRI)-guided laser ablation has been extensively evaluated in Europe and has a reported survival of 94%, 77%, 56%, and 37% at 1, 2, 3, and 5 years, respectively.

A “test-of-time” management approach involves reimaging patients 3-4 months after determination of suitability for resection. Interval development of hepatic metastases prevents patients from undergoing an unnecessary, noncurative surgery. The surgical rationale in these cases is that these new tumors would have developed shortly after surgery, had surgery been immediate, and the patient would not have benefited from a major operation. RFA has been applied in the interval between selection and resection to prevent progression of the existing tumors. Those who develop new metastases can be spared a noncurative operation. Those who demonstrate only local progression of the ablated tumor can still undergo surgery. Those who show no viable tumor have the option of surgery or close surveillance.

Image-Guided Ablation for Other Hepatic Metastases and Tumors

Ablation has been applied to pancreatic, breast, ovarian, sarcomas, ocular melanoma, and neuroendocrine metastases to the liver.

There are limited data on the use of RFA in treating hepatic metastases from breast cancer. Breast cancer is a systemic disease, and systemic therapy remains the primary means of therapy. In 3%-12% of patients, metastases are only in the liver. These patients as well as those who have liver-dominant metastases are those who are likely to benefit the most from ablation. Local control can be achieved in 92% of tumors. Enthusiasm for percutaneous ablation is mitigated by the fact that new metastases develop in 60% of patients.

Neuroendocrine metastases to the liver can be ablated for palliation of hormonal symptoms. However, the extent of disease often makes transcatheter embolization a more effective option.

Standard management of advanced (stages III and IV) ovarian cancer involves surgical resection and chemotherapy. Thermal ablation is effective in achieving local control in selected patients with limited metastasis from ovarian cancer.

Hepatic adenoma has a malignant potential. Image-guided ablation has been used to treat solitary small hepatic adenomas that are unsuitable for resection or as an alternative when resection is rejected.