Synonyms

Local ablation therapy

Definition

There has been no clear definition for locoregional therapy. Most often, locoregional therapy refers to various minimally invasive therapeutic procedures. With the aid of ultrasound guidance, an antitumoral device, drug, or chemical is introduced directly into the tumor and causes tumor death.

Characteristics

For most human cancers, surgical resection remains the standard treatment modality. However, resection is sometimes possible in only a minority of patients. When surgical treatment is less likely to perform, physicians may choose other therapeutic procedures. Among the available methods, locoregional therapy has been frequently used to treat cancer. It is so named because the tumors can often be treated locally. The best example to demonstrate the role and usefulness of locoregional therapy is applying this kind of therapy in patients with hepatocellular carcinoma, or HCC, which is primary liver cancer originated from transformed liver cells. HCC is one of the common malignant tumors in the world, and most cases are found in Asia and Africa. Among the various locoregional interventions, transarterial chemoembolization, percutaneous ultrasound-guided therapy including injection of ethanol or acetic acid, and thermal ablation using radiofrequency and microwave energy, are the most commonly used methods (Table 1). These locoregional therapies possess the advantages of preserving the uninvolved liver parenchyma and avoiding potential morbidity and mortality of major hepatic surgery.

Locoregional Therapy. Table 1 Comparison of various locoregional therapies for HCC
Full size table

Transarterial Chemoembolization (TACE)

Most liver cancers, when formed, have a feeding artery that delivers nutrition and oxygen to tumor cells to enable their growth. TACE, using iodized oil and chemotherapeutic agents, combines the effect of targeted chemotherapy with that of ischemic necrosis induced by arterial embolization. Although TACE was originally used for metastatic liver tumors from colorectal cancers or other malignancies, it was later used to treat primary HCC because HCC nodule frequently has a high arterial blood supply (hypervascular lesion). In addition, TACE can target single- or multi-nodular HCCs in one treatment session and could be repeatedly administered. TACE is generally a palliative treatment for unresectable HCC, and a better outcome can only be expected in properly selected patients.

Percutaneous Ethanol Injection (PEI)

PEI was originally developed in the 1980s when the real time ultrasound-guided aiming became possible. The injected chemical, pure ethanol, induces local tumor necrosis as a result of direct protein denature, cellular dehydration, and thrombosis of blood vessels. HCC usually is hypervascular and well-encapsulated by a tumor capsule that can limit the spread of ethanol. These characteristics have made PEI one of the most commonly used methods of local ablation therapy. Usually PEI is limited to patients with small-sized tumor nodules. Compared with the transarterial approach, PEI has the advantages of being safer, less expensive, and easy to perform. In addition, PEI allows selective treatment of HCC without significant damage to the adjacent liver parenchyma, and can be used for patients with moderately advanced cirrhosis. Side effects are mostly minimal.

Percutaneous Acetic Acid Injection (PAI)

Acetic acid induces profound tumor necrosis at a concentration of 15–50% through a similar mechanism as ethanol. It has a strong ability to penetrate cancer cells, and can dissolve lipids and extract collagen from intratumoral septa and capsule that frequently contain viable cancer cells. Therefore, acetic acid is at least equally effective compared with ethanol in treating HCC.

Radiofrequency Ablation (RFA)

RFA for human HCC was first reported in the mid-1990s. The puncture needle (or probe) has an insulated shaft and a noninsulated tip, which is inserted into the lesion under ultrasound or computed tomography guidance. The patient is part of the electric circuit with grounding pads on the thighs or the back. The radiofrequency energy emitted from the needle tip induces ionic agitation and frictional heat. The surrounding tissue, rather than the electrode itself, is the source of heat that destroys the cancer cells. RFA has now become one of the very efficient local ablative therapies for HCC due to its excellent necrotizing effect. While many investigators consider RFA a safe procedure, a few reports found that the complication rate of RFA could be quite high. When the location of tumor nodule is close to the major blood vessels, the radiofrequency energy will be carried away by the blood flow (the “heat sink” phenomenon) and result in a suboptimal treatment response.

Microwave Coagulation Therapy (MCT)

As a thermal ablation method for HCC, MCT utilizes a microwave coagulator that generates and transmits microwave energy to a needle electrode which is inserted into the lesion. MCT has been studied in patients with HCC as well as in liver metastasis. It can be applied with percutaneous or laparoscopic approach to ablate unresectable HCC, and is useful to control tumor bleeding from ruptured HCC or prevent massive blood loss in liver surgery.

Comments

Locoregional therapy has also been applied to other cancers other than HCC, but the overall experience is relatively limited. The choice and application of various locoregional therapies for HCC and other cancers may vary from center to center and is likely to depend on the experience, preference, and facility of the referral center. Long-term survival in patients with unresectable HCC may be achievable in selected patients provided various locoregional therapies can be appropriately performed.