Long-term Survival of Patients with Unresectable Colorectal Liver Metastases treated by Percutaneous Interstitial Laser Thermotherapy

Laser Ablation for Cancer: Past, Present and Future

Laser ablation (LA) is gaining acceptance for the treatment of tumors as an alternative to surgical resection. This paper reviews the use of lasers for ablative and surgical applications. Also reviewed are solutions aimed at improving LA outcomes: hyperthermal treatment planning tools and thermometric techniques during LA, used to guide the surgeon in the choice and adjustment of the optimal laser settings, and the potential use of nanoparticles to allow biologic selectivity of ablative treatments. Promising technical solutions and a better knowledge of laser-tissue interaction should allow LA to be used in a safe and effective manner as a cancer treatment.

CT-guided high-dose-rate brachytherapy in the interdisciplinary treatment of patients with liver metastases of pancreatic cancer

BACKGROUND

CT-guided high-dose-rate brachytherapy (CT-HDRBT) is an interventional radiologic technique for local ablation of primary and secondary malignomas applying a radiation source through a brachycatheter percutaneously into the targeted lesion. The aim of this study was to assess local tumor control, safety and efficacy of CT-HDRBT in the treatment of liver metastases of pancreatic cancer.

METHODS

Twenty consecutive patients with 49 unresectable liver metastases of pancreatic cancer were included in this retrospective trial and treated with CT-HDRBT, applied as a single fraction high-dose irradiation (15-20 Gy) using a 192Ir-source. Primary endpoint was local tumor control and secondary endpoints were complications, progression-free survival and overall survival.

RESULTS

The mean tumor diameter was 29 mm (range 10-73). The mean irradiation time was 20 minutes (range 7-42). The mean coverage of the clinical target volume was 98% (range 88%-100%). The mean D100 was 18.1 Gy and the median D100 was 19.78 Gy. Three major complications occurred with post-interventional abscesses, three of which were seen in 15 patients with biliodigestive anastomosis (20%) and overall 15%. The mean follow-up time was 13.7 months (range 1.4-55.0). The median progression-free survival was 4.9 months (range 1.4-42.9, mean 9.4). Local recurrence occurred in 5 (10%) of 49 metastases treated. The median overall survival after CT-HDRBT was 8.6 months (range 1.5-55.3). Eleven patients received chemotherapy after ablation with a median progression-free survival of 4.9 months (mean 12.9). Nine patients did not receive chemotherapy after intervention with a median progression-free survival of 3.2 months (mean 5.0). The rate of local tumor control was 91% in both groups after 12 months.

CONCLUSION

CT-HDRBT was safe and effective for the treatment of liver metastases of pancreatic cancer.

Colorectal cancer liver metastases: long-term survival and progression-free survival after thermal ablation using magnetic resonance-guided laser-induced interstitial thermotherapy in 594 patients: analysis of prognostic factors

PURPOSE

The purpose of this study was the evaluation of prognostic factors for long-term survival and progression-free survival (PFS) after treatment of colorectal cancer (CRC) liver metastases with magnetic resonance-guided laser-induced interstital thermotherapy (LITT).

PATIENTS AND METHODS

We included 594 patients (mean age, 61.2 years) with CRC liver metastases who were treated with LITT. The statistical analysis of the long-term survival and PFS were based on the Kaplan-Meier method. The Cox regression model tested different parameters that could be of prognostic value. The tested prognostic factors were the following: sex, age, the location of primary tumor, the number of metastases, the maximal diameter and total volume of metastases and necroses, the quotient of total volumes of metastases and necroses, the time of appearance of liver metastases and location in the liver, the TNM classification of CRC, extrahepatic metastases, and neoadjuvant treatments.

RESULTS

The median survival was 25 months starting from the date of the first LITT. The 1-, 2-, 3-, 4-, and 5-year survival rates were 78%, 50.1%, 28%, 16.4%, and 7.8%, respectively. The median PFS was 13 months. The 1-, 2-, 3-, 4-, and 5-year PFS rates were 51.3%, 35.4%, 30.7%, 25.4%, and 22.3%, respectively. The number of metastases and their maximal diameter were the most important prognostic factors for both long-term survival and PFS. Long-term survival was also highly influenced by the initial involvement of the lymph nodes.

CONCLUSIONS

For patients treated with LITT for CRC liver metastases, the number and size of metastases, together with the initial lymph node status, are significant prognostic factors for long-term survival.

Understanding the current status of image-guided ablation for metastatic colorectal disease

Colorectal metastases to the liver are increasingly being detected and accurately characterized at an earlier stage and even at the subcentimeter level. The oncological case for surgical resection of this disease is widely accepted. The advent of smaller volume disease has encouraged the development of in situ ablative technologies over the last two decades and the oncological efficacy of these procedures has continued to improve through stepwise developments in ablation devices and image guidance. This article provides an overview of these techniques, currently available and future technologies, and the imaging findings encountered. It also sets out the current position image-guided ablation merits alongside chemotherapy and surgical resection. In selected cases ablation for colorectal metastases can produce oncological outcomes equivalent to surgery and critically with less morbidity in an increasingly older patient population. We examine whether with careful patient selection, optimal technology, meticulous technique, and diligent follow-up, consistently reproducible high quality outcomes will be achieved in the next few years.

Thermal ablation of liver metastases from colorectal cancer: radiofrequency, microwave and laser ablation therapies

Surgery is currently considered the treatment of choice for patients with colorectal cancer liver metastases (CRLM) when resectable. The majority of these patients can also benefit from systemic chemotherapy. Recently, local or regional therapies such as thermal ablations have been used with acceptable outcomes. We searched the medical literature to identify studies and reviews relevant to radiofrequency (RF) ablation, microwave (MW) ablation and laser-induced thermotherapy (LITT) in terms of local progression, survival indexes and major complications in patients with CRLM. Reviewed literature showed a local progression rate between 2.8 and 29.7 % of RF-ablated liver lesions at 12-49 months follow-up, 2.7-12.5 % of MW ablated lesions at 5-19 months follow-up and 5.2 % of lesions treated with LITT at 6-month follow-up. Major complications were observed in 4-33 % of patients treated with RF ablation, 0-19 % of patients treated with MW ablation and 0.1-3.5 % of lesions treated with LITT. Although not significantly different, the mean of 1-, 3- and 5-year survival rates for RF-, MW- and laser ablated lesions was (92.6, 44.7, 31.1 %), (79, 38.6, 21 %) and (94.2, 61.5, 29.2 %), respectively. The median survival in these methods was 33.2, 29.5 and 33.7 months, respectively. Thermal ablation may be an appropriate alternative in patients with CRLM who have inoperable liver lesions or have operable lesions as an adjunct to resection. However, further competitive evaluation should clarify the efficacy and priority of these therapies in patients with colorectal cancer liver metastases.

Magnetic resonance-guided laser-induced interstitial thermotherapy of breast cancer liver metastases and other noncolorectal cancer liver metastases: an analysis of prognostic factors for long-term survival and progression-free survival

PURPOSE

The purpose of this study was the evaluation of prognostic factors for long-term survival and progression-free survival (PFS) after treatment of noncolorectal cancer liver metastases through MR-guided laser-induced thermotherapy (LITT).

PATIENTS AND METHODS

We included 401 patients (mean age, 57.3 years) with liver metastases from different primary tumors who were treated with LITT. Long-term survival and progression-free-survival rates were evaluated using the Kaplan-Meier method. A Cox regression model tested different parameters that could be of prognostic value. The tested prognostic factors were as follows: the location of primary tumor, TNM classification, extrahepatic metastases, hepatic resection or neoadjuvant transarterial chemoembolization or systemic chemotherapy before LITT, the number of initial metastases, the volume of metastases, and the quotient of total volumes of metastases and necroses per patient.

RESULTS

The median survival was 37.6 months starting from the date of LITT. The 1-, 2-, 3-, 4-, and 5-year survival rates were 86.5%, 67.2%, 51.9%, 39.9%, and 33.4%, respectively. The median PFS was 12.2 months. The 1-, 2-, 3-, 4-, and 5-year PFS rates were 50.6%, 33.8%, 26%, 20.4%, and 17%, respectively. The initial number of metastases, the volumes of metastases, and the quotient of the volumes of metastases and necroses influenced the long-term survival and the PFS.

CONCLUSIONS

Laser-induced thermotherapy is a minimally invasive method in the treatment of hepatic metastases of noncolorectal cancer, and it shows good results in long-term survival and PFS. The initial number of metastases and their volume are the most important prognostic factors. The status of the lymph nodes, the existence of other extrahepatic metastases, the location of the primary tumor, and different neoadjuvant therapies are of nonprognostic value.

Repeated transarterial chemoembolisation using different chemotherapeutic drug combinations followed by MR-guided laser-induced thermotherapy in patients with liver metastases of colorectal carcinoma

BACKGROUND

To evaluate a treatment protocol with repeated transarterial-chemoembolisation (TACE) downsizing before MR-guided laser-induced interstitial thermotherapy (LITT) using different chemotherapeutic combinations in patients with unresectable colorectal cancer (CRC) liver metastases.

METHODS

Two hundred and twenty-four patients were included in the current study. Transarterial-chemoembolisation (mean 3.4 sessions per patient) was performed as a downsizing treatment to meet the LITT requirements (number5, diameter <5 cm). The intra-arterial protocol consisted of either Irinotecan and Mitomycin (n=77), Gemcitabine and Mitomycin (n=49) or Mitomycin alone (n=98) in addition to Lipiodol and Embocept in all patients. Post TACE, all patients underwent LITT (mean 2.2 sessions per patient).

RESULTS

Overall, TACE resulted in a mean reduction in diameter of the target lesions of 21.4%. The median time to progression was 8 months, calculated from the start of therapy and the median local tumour control rate was 7.5 months, calculated as of therapy completion. Median survival of patients calculated from the beginning of TACE was 23 months (range 4-110 months), in patients treated with Irinotecan and Mitomycin the median was 22.5 months, Gemcitabine and Mitomycin 23 months and Mitomycin only 24 months with a statistically significant difference between the groups (P<0.01).

CONCLUSION

Repeated TACE offers adequate downsizing of CRC liver metastases to allow further treatment with LITT. The combined treatment illustrates substantial survival rates and high local tumour control with statistically significant differences between the three protocols used. Further randomised trials addressing the current study results are required.

Changes in growth factor levels after thermal ablation in a murine model of colorectal liver metastases

OBJECTIVES

This study examines changes in the expression of growth factors following thermal ablation (TA) of selected colorectal cancer (CRC) liver metastases.

METHODS

Using mice with established CRC liver metastases, two tumours in each animal were thermally ablated. Liver and tumour tissues were collected at various time-points (days 0, 1, 2, 3, 5 and 7) following TA treatment from the ablation site and from sites distant from ablated tumour. Changes in growth factor expression (epidermal growth factor [EGF], vascular endothelial growth factor [VEGF], hepatocyte growth factor [HGF] and transforming growth factor-β[TGF-β]) in comparison with baseline levels (non-ablated) were assessed by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry.

RESULTS

Baseline TGF-β and VEGF levels in the liver parenchyma of tumour-bearing mice were significantly higher than levels in naive liver parenchyma. Levels of VEGF and HGF decreased after TA treatment in all tissues. Levels of EGF decreased in ablated and distant tumour tissues, but displayed a tendency to increase in liver tissue. Levels of TGF-β also decreased during the first 2 days following TA, but later increased in liver and tumour tissues distant from the ablation site to a level that reached significance in tumour tissue at day 7 (P < 0.001). Decreases in growth factor levels were also observed in animals that underwent laparotomy without TA treatment, which indicates that these decreases were caused by the experimental procedure.

CONCLUSIONS

Tumour induces upregulation of TGF-β and VEGF in liver parenchyma. Growth factors decreased after TA, but this appears to be the result of the experimental procedure rather than the TA itself. However, TA resulted in increased levels of TGF-β, which may contribute to tumour recurrence.

Principles of and advances in percutaneous ablation

Image-guided tumor ablation with both thermal and nonthermal sources has received substantial attention for the treatment of many focal malignancies. Increasing interest has been accompanied by continual advances in energy delivery, application technique, and therapeutic combinations with the intent to improve the efficacy and/or specificity of ablative therapies. This review outlines clinical percutaneous tumor ablation technology, detailing the science, devices, techniques, technical obstacles, current trends, and future goals in percutaneous tumor ablation. Methods such as chemical ablation, cryoablation, high-temperature ablation (radiofrequency, microwave, laser, and ultrasound), and irreversible electroporation will be discussed. Advances in technique will also be covered, including combination therapies, tissue property modulation, and the role of computer modeling for treatment optimization.

[Interventional procedures for hepatic metastases]

The therapeutic concept for hepatic metastases is mainly based on surgical resection and systemic chemotherapy. Considering technical respectability, oncological significance and limiting comorbidities, only 10-30% of patients with hepatic metastases can undergo surgery with a curative intention. Patients assessed as being non-resectable qualify in general for (palliative) chemotherapy. However, for many patients surgical therapy of the liver is no longer possible due to medical or technical reasons, nevertheless, the total tumor load is still limited, which makes an interventional, local ablative therapy approach promising, with and without chemotherapy. Thus, various interventional-radiological, minimally invasive techniques could be successfully established as oncological therapy components besides surgery and chemotherapy. These types of intervention encompass mainly chemotherapy (percutaneous alcohol instillation, transarterial chemoembolization and transarterial chemotherapy), thermotherapy (radiofrequency, laser and microwave ablations) and radio-ablative procedures (radio-embolization, selective internal radiation therapy SIRT, interstitial and catheter-guided brachytherapy). Incorporating these procedures into therapeutic multimodal concepts inaugurates a significantly broadened therapy spectrum with a clear additional improvement in patient prognosis.

Systematic review of tumour number and outcome after radical treatment of colorectal liver metastases

Background

Resection of colorectal liver metastases (CLMs) is potentially curative but the effect of tumour number on prognosis is uncertain. This study compared the prognosis after resection and/or ablation of between one and three, or four or more CLMs.

Methods

A systematic literature review from January 2000 to June 2008 was performed. Study selection and data extraction were standardized, and analysis included assessment of methodological quality, heterogeneity and bias. Main outcomes were 3- and 5-year survival. A meta-analysis comparing radical treatment in the two groups was performed using the hazard ratio for overall survival.

Results

Of 1307 studies screened, 46 (9934 patients) were included in the analysis. Methodological quality was variable, and there was significant heterogeneity and reporting bias. The overall 5-year survival rate after radical treatment ranged from 7 to 58 per cent. Pooled hazard ratio for overall survival was 1·67 (95 per cent confidence interval 1·43 to 1·95; P &lt; 0·001). Median reported 5-year survival for patients with four or more CLMs was 17·1 per cent.

Conclusion

Radical treatment of more than three CLMs results in poorer overall survival. Nevertheless, 5-year survival is achievable and the number of lesions should not, of itself, be used to exclude patients from surgery.

Inoperable colorectal liver metastases: a declining entity?

BACKGROUND

Untreated colorectal liver metastases (CLMs) have a dismal prognosis. Surgery remains the gold standard of treatment, but many patients will have inoperable disease at presentation. Until recently, the outlook for such patients was bleak. The purpose of this review was to report on available options in the treatment CLMs, which would be considered unresectable by conventional evaluation.

METHODS

Inclusion criteria were articles published in English-language journals reporting on either retrospective or prospective cohorts of patients undergoing treatment for conventionally inoperable CLM. Main outcome measures were survival, resectability rates, morbidity and mortality following treatment of the patients' disease.

RESULTS

Improved chemotherapy regimes and other innovative treatments have opened up new options for such patients and may even render conventionally inoperable disease resectable. The aim of treatment should be down-staging of metastases to achieve resectability, however, other treatments such as ablation may be also be used (either alone or in conjunction with resection).

CONCLUSION

A nihilistic attitude to the patient with seemingly inoperable liver metastases should be discouraged. Discussion of such patients at multi-disciplinary meetings is essential in order to plan and monitor treatments.

Vascular targeting agent Oxi4503 inhibits tumor growth in a colorectal liver metastases model

BACKGROUND AND AIM

Oxi4503 is a potent vascular targeting agent belonging to the family of combretastatins. These agents produce an acute reduction in tumor blood flow leading to tumor necrosis. Despite evidence of its efficacy in certain malignancies, the effect on colorectal liver metastases remains largely unknown. This study investigates the effect of Oxi4503 on colorectal liver metastases in a murine model.

METHODS

The effect of a single dose of Oxi4503 on established tumors in a murine model of colorectal liver metastases was assessed following administration of 1-50 mg/kg Oxi4503. In addition, the effects of continuous, daily and intermittent dosing (1-5 mg/kg) on tumor necrosis and growth were studied by quantitative histological and stereological analysis. The effect of multiple dosing on long-term survival was also assessed using the Kaplan-Meier analysis. The microvascular effects of therapy were studied by scanning electron microscopy of microvascular resin casts.

RESULTS

A single dose of 5 or 50 mg/kg of Oxi4503 produced significant tumor necrosis compared to the controls. Subcutaneous continuous dosing infusion with Oxi4503 at 1 mg/kg/day reduced tumor growth compared to the controls, but was associated with marked systemic toxicity. Daily administration over 21 days was associated with significant mortality. Intermittent dosing of Oxi4503 (two doses, 3 days apart) produced the greatest reduction in tumor growth with minimal toxicity and conferred a significant survival advantage. Microvascular casts demonstrated significant disruption of tumor vessels.

CONCLUSIONS

A single dose of Oxi4503 produced significant necrosis and microvascular injury in colorectal liver metastases. Intermittent dosing with Oxi4503 produced the maximum reduction in tumor growth, minimal toxicity, and a significant improvement in survival. Oxi4503 is a potential anticancer agent. Further research into its mechanism of action and its synergistic use with other therapies is warranted.

Expanding criteria for resectability of colorectal liver metastases

Surgical resection is the treatment of choice in patients with colorectal liver metastases, with 5-year survival rates reported in the range of 40%-58%. Over the past 10 years, there has been an impetus to expand the criteria for defining resectability for patients with colorectal metastases. In the past, such features as the number of metastases (three to four), the size of the tumor lesion, and a mandatory 1-cm margin of resection dictated who was "resectable." More recently, the criteria for resectability have been expanded to include any patient in whom all disease can be removed with a negative margin and who has adequate hepatic volume/reserve. Specifically, instead of resectability being defined by what is removed, decisions concerning resectability now center around what will remain after resection. Under this new paradigm, the number of patients with resectable disease can be expanded by increasing/preserving hepatic reserve (e.g., portal vein embolization, two-stage hepatectomy), combining resection with ablation, and decreasing tumor size (preoperative chemotherapy). The criteria for resectability have also expanded to include patients with extrahepatic disease. Rather than being an absolute contraindication to surgery, patients with both intra- and extrahepatic disease should potentially be considered for resection based on strict selection criteria. The expansion of criteria for resectability of colorectal liver metastases requires a much more nuanced and sophisticated approach to the patient with advanced disease. A therapeutic approach that includes all aspects of multidisciplinary and multimodality care is required to select and treat this complex group of patients.

Efficacy of direct electrical current therapy and laser-induced interstitial thermotherapy in local treatment of hepatic colorectal metastases: an experimental model in the rat

BACKGROUND

Local antitumoral therapy of metastases is an important tool in the palliative treatment of advanced colorectal cancer. Several authors have recently reported on successful local treatment of different malignant diseases with low-level direct current therapy. The aim of the present study was to compare the effectiveness of direct current therapy with the established laser-induced thermotherapy (LITT) on experimental colorectal liver metastases.

MATERIALS AND METHODS

Colorectal metastases were induced in 49 BD IX rats by injection of colon cancer cells beneath the liver capsule. Three weeks after induction, tumor volumes and sizes were estimated with magnetic resonance imaging and by manual measurement of the largest tumor diameter, and two treatment groups and two control groups were established. Direct current (80 C/cm(3)) versus LITT (2 W; 5 to 10 min) was locally applied via laparotomy. Control groups were sham treated. Tumor growth was analyzed 5 wk after therapy by manual measurement of the maximal diameter and histopathological examination was performed.

RESULTS

Measurement of tumor sizes 5 wk after therapy confirmed a significant antitumoral effect of direct current (1.6-fold tumor enlargement) and of LITT (1.3-fold tumor enlargement), compared with controls (2.8-fold and 2.9-fold tumor enlargement). However, after 5 wk, LITT was significantly more effective in limiting tumor growth than direct current treatment (P </= 0,001). Histopathological analysis revealed a complete response rate of 21% and a partial response rate of 77% in the electric current group. In comparison, LITT treated livers showed a complete response rate of 22% and a partial response rate of 78% (n.s.).

CONCLUSIONS

The data confirm that direct current therapy and LITT are effective treatment strategies in the palliative control of colorectal hepatic metastases, with both therapies being equally effective in inducing a complete or partial tumor necrosis.

Surgical therapy for colorectal metastases to the liver

Colorectal cancer is the fourth most common type of cancer in the West and the second leading cause of cancer-related deaths in the United States. Approximately 35 to 55% of patients with colorectal cancer develop hepatic metastases during the course of their disease. Surgical resection of colorectal liver metastases represents the only chance at potential cure, and long-term survival can be achieved in 35 to 58% of patients after resection. The goal of hepatic resection should be to resect all metastases with negative histologic margins while preserving sufficient functional hepatic parenchyma. In patients with extensive metastatic disease who would otherwise be unresectable, ablative approaches can be used instead of or combined with hepatic resection. The use of portal vein embolization and preoperative chemotherapy may also expand the population of patients who are candidates for surgical treatment. Despite these advances, many patients still experience a recurrence after hepatic resection. More active systemic chemotherapy agents are now available and are being increasingly employed as adjuvant therapy either before or after surgery. Modern treatment of colorectal liver metastasis requires a multidisciplinary approach in an effort to increase the number of patients who may benefit from surgical treatment of colorectal cancer liver metastasis.

Selective portal clamping to minimize hepatic ischaemia-reperfusion damage and avoid accelerated outgrowth of experimental colorectal liver metastases

BACKGROUND

Temporary vascular clamping during local ablation for colorectal liver metastases increases destruction volumes. However, it also causes ischaemia-reperfusion (IR) injury to the liver parenchyma and accelerates the outgrowth of microscopic tumour deposits. The aim of this study was to investigate the effects of selective portal clamping on hepatocellular damage and tumour growth.

METHODS

Mice carrying pre-established hepatic colorectal micrometastases underwent either simultaneous clamping of both the portal vein and the hepatic artery or selective clamping of the portal vein to the median and left liver lobes for 45 min. Sham-operated mice served as controls. Hepatic injury and tumour growth were assessed over time.

RESULTS

Standard inflow occlusion resulted in a rise in liver enzymes, a local inflammatory response and hepatocellular necrosis. The outgrowth of pre-established micrometastases was accelerated three- to fourfold in clamped compared with non-clamped liver lobes (27.4 versus 7.8 per cent, P < 0.010). Conversely, selective portal clamping induced minimal liver injury, tissue inflammation or hepatocellular necrosis, and completely stopped the accelerated outgrowth of micrometastases.

CONCLUSION

Selective portal clamping does not induce liver tissue damage or accelerate micrometastasis outgrowth and may therefore be the preferable clamping method during local ablative treatment of hepatic metastases.

Image-Guided Microtherapy for Tumor Ablation: From Thermal Coagulation to Advanced Irradiation Techniques

Image-guided tumor ablation has been established as a valuable adjunct in oncological treatment concepts. The majority of micro-therapeutic procedures is performed by applying thermal ablation, such as radiofrequency or laser. However, in view of the limitations of thermal ablation regarding tumor size or adjacent risk structures, novel techniques combining brachytherapy with modern interventional techniques have demonstrated favorable outcomes. In addition, advances in non-invasive percutaneous irradiation, such as extracranial stereotaxy, have demonstrated very competitive preliminary results. In this article, state-of-the-art techniques for micro-therapeutic tumor ablation are being described.

[Nonoperative ablation for liver metastases. Possibilities and limitations as a curative treatment]

Under the term "nonoperative ablation" are grouped a number of heterogeneous approaches for the treatment of liver metastases, including laser-induced thermotherapy (LITT), radio-frequency therapy (RF), and cryotherapy. In general these procedures had been intended only for palliative purposes. The establishment of clinically relevant lesion size and a lack of long-term survival data were regarded as main limitations to using them with curative intention. During the last years however, new application systems have demonstrated remarkable results in RF and LITT, and some clinical studies have shown long-term survival in selected patients comparable to that for hepatic resection. We review possibilities and limitations of nonoperative ablation procedures with curative intent, highlighting the histopathological bases of thermal ablation techniques and clinical aspects such as R0 ablation and long-term survival.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

Focal heat destruction has emerged as an effective treatment strategy in selected patients with malignant liver tumors. Radiofrequency ablation, interstitial laser thermotherapy, and microwave treatment are currently the most widely applied thermal ablative techniques. A major limitation of these therapies is incomplete tumor destruction and overall high recurrences. An understanding of the mechanisms of tissue injury induced by focal hyperthermia is essential to ensure more complete tumor destruction. Here, the currently available scientific literature concerning the underlying mechanisms involved in the destruction of liver tumors by focal hyperthermia is reviewed.

METHODS

Medline was searched from 1960 to 2004 for literature regarding the use of focal hyperthermia for the treatment of liver tumors. All relevant literature was searched for further references.

RESULTS

Experimental evidence suggests that focal hyperthermic injury occurs in two distinct phases. The first phase results in direct heat injury that is determined by the total thermal energy applied, tumor biology, and the tumor microenvironment. Tumors are more susceptible to heat injury than normal cells as the result of specific biological features, reduced heat dissipating ability, and lower interstitial pH. The second phase of hyperthermic injury is indirect tissue damage that produces a progression of tissue injury after the cessation of the initial heat stimulus. This progressive injury may involve a balance of several factors, including apoptosis, microvascular damage, ischemia-reperfusion injury, Kupffer cell activation, altered cytokine expression, and alterations in the immune response. Blood flow modulation and administration of thermosensitizing agents are two methods currently used to increase the extent of direct thermal injury. The processes involved in the progression of thermal injury and therapies that may potentially modulate them remain poorly understood.

CONCLUSION

Focal hyperthermia for the treatment of liver tumors involves complex mechanisms. Evidence suggests that focal hyperthermia produces both direct and indirect tissue injury by differing underlying processes. Methods to enhance the effects of treatment to achieve complete tumor destruction should focus on manipulating these processes.