Vascular malformations are a rare condition caused by abnormally developed blood vessels. They can occur anywhere in the body and range from simple and benign to complex conditions, with an incidence of around 1.5% in the general population.
The latest and most used categorization is the International Society for the Study of Vascular Anomalies (ISSVA) classification (Table 1).1 This classification divides vascular anomalies into two main categories: tumors (true proliferative neoplasms) and malformations (morphogenetic defects). These two categories are further subcategorized: tumors are divided into benign, locally aggressive/borderline and malignant, whereas malformations are subdivided into simple, combined or associated with other anomalies. Clinically, vascular anomalies can also be divided into low-flow and high-flow malformations.2
International Society for the Study of Vascular Anomalies (ISSVA) classification for vascular anomalies 2018
Infantile hemangioma | Kaposiform hemangioendothelioma | Capillary malformation (CM) | CVM, CLM | |
Congenital hemangioma | Retiform hemangioendothelioma | Lymphatic malformation (LM) | LVM. CLVM | |
Tufted hemangioma | PILA. Dabska tumor | Epithelioid hemangioendothelioma | Venous malformation (VM) | CAVM |
Spindle-cell hemangioma | Composite hemangioendothelioma | Angiosarcoma | Arteriovenous malformation (AVM) | |
Epithelioid hemangioma | Kaposi sarcoma | Arteriovenous fistula | CLAVM | |
Pyogenic granuloma |
AVM = arteriovenous malformation; CAVM = capillary arteriovenous malformation; CLAVM = capillary lymphatic arteriovenous malformation; CLM = capillary lymphatic malformations; CLVM = capillary lymphatic venous malformation; CM = capillary malformation; CVM = capillary venous malformations; LM = lymphatic malformation; LVM = lymphatic venous malformation; PILA – papillary intralymphatic angioendothelioma; VM - venous malformation
Current approaches vary depending on the type and anatomical location of the vascular malformation. Treatment options include observation, sclerotherapy, laser therapy, embolization, and surgery.3,4 Observation is recommended for asymptomatic superficial or low-flow malformations that pose no immediate risk to the patient and are stable in size. Sclerotherapy involves the injection of sclerosing agents, such as bleomycin, or other agents (pingyangmycin, absolute ethanol, ethanolamine oleate, polidocanol, doxycycline, cyanoacrylate, sodium morrhuate and sodium tetradecyl sulfate (STS)).5,6 Laser therapy is used to treat superficial vascular malformations and involves the use of a laser to heat the affected area and reduce vessel size. Embolization is a minimally invasive procedure in which small particles, metal coils, or solidifying liquid agents are injected into the malformation to block the flow of blood and reduce its size. This treatment is typically used for high-flow malformations. Surgery may be necessary for high-flow malformations that are difficult to treat with the other methods mentioned. Depending on the size and anatomical location, the surgeon may only remove part of the lesion.7
There are several
There are three underlying
The second mechanism is the induction of the immune response due to immunogenic tumor cell death induced by the drug. It is well known that certain ablative therapies induce immunogenic cell death that can attract and boost the immune response of the organism. This mechanism has been described in radiation therapy, thermal ablative techniques, and electrochemotherapy.10,12,19 Several groups have investigated the role of immunogenic cell death in the effectiveness of electrochemotherapy. Now, the experimental data indicate that the response of the tumors varies depending on the immunogenicity of the tumors; more immunogenic tumors respond better to electrochemotherapy than less immunogenic tumors, which was linked to more pronounced immunogenic cell death after electrochemotherapy.10,12,20 Additionally, clinical data on the treatment of melanoma demonstrate that local treatment of cutaneous metastases can boost or interact with treatment using immune checkpoint inhibitors, such as pembrolizumab.21 Patients treated with both electrochemotherapy and immune checkpoint inhibitors had lower disease progression rates and longer survival than those who received pembrolizumab only.
The third mechanism is the vascular disrupting effect of electrochemotherapy. In early preclinical research, it was established that the application of electric pulses only temporarily abrogates blood flow within tumors. This phenomenon was termed vascular lock and lasts less than an hour.22,23 Furthermore, the effect is enhanced when the drug is present during application of the electric pulses. Investigations have shown that it results in vascular disruption that occurs within hours in tumors. Endothelial cells start to die, blood flow is obstructed, and secondary tumor cell death is induced within days due to induced tumor hypoxia.24,25,26,27 The phenomenon is predominantly confined to the tumor vasculature, sparing the normal vasculature around the tumors. The reason for this is because of the high proliferation rate of endothelial cells in tumors compared to the vasculature in normal tissues, where the endothelial proliferation rate is very slow. The vascular disrupting effect of electrochemotherapy is not fully understood. To date, we do not know in what proportion this vascular disrupting effect contributes to the overall effectiveness of electrochemotherapy in specific tumor types. We know that it is dependent on the distribution and extent of tumor vascularization, and better vascularized tumors respond better to electrochemotherapy.28,29 Preclinical data also indicate that tumor perfusion influences the effectiveness of the treatment, with well perfused tumors showing an improved response.30
Electrochemotherapy is safely applied to palliate bleeding cutaneous metastases and treat vascular tumors e.g., Kaposi sarcoma, superficial angiosarcoma31,32,33,34 and highly vascularized liver metastases.35,36 Bleeding after the insertion of needle electrodes quickly stops due to vascular lock.37 Additionally, both superficial and liver tumors themselves also do not bleed after electrochemotherapy due to the vascular disrupting effect. These observations indicate that electrochemotherapy indeed exerts vascular effects, the abovementioned vascular lock and the vascular disrupting effect. Furthermore, several reports indicate that electrochemotherapy can be safely applied to control or treat bleeding tumors.37 Of note, bleeding stops almost immediately after the application of electric pulses; therefore, treatment of bleeding tumors is also one of the indications for electrochemotherapy (Figure 1).
These data support the potential advantage of bleomycin electrosclerotherapy in the treatment of vascular malformations. Bleomycin is already one of the most frequently used sclerotherapy agents in the treatment of these lesions.5,6 Therefore, the combination with electric pulses may only add to the effectiveness of bleomycin since it would increase the uptake of the drug into the endothelial lining of the affected blood vessels. In many cases, blood vessels are abnormal and endothelial cell proliferation is higher than that in normal blood vessels.38 Therefore, the vasculature in vascular malformations is impaired as it is in tumors, and electrochemotherapy is supposed to be effective in both.
Histological evidence from liver biopsies indicates that venules are more sensitive to electrochemotherapy than arterioles in normal liver parenchyma.39 This would indicate that venous malformations would have been more susceptible to BEST.
We recently performed a study on pigs investigating vascular changes in large blood vessels such as the portal vein, inferior vena cava, and lineal vein. In this study, the vessels were directly exposed to electroporation and electrochemotherapy by the application of electric pulses using plate electrodes that embraced the vessels. Electrochemotherapy may temporarily disrupt the endothelial lining and disrupt the vasa vasorum of the vessels (unpublished data). This effect may, however, be a desired one in the treatment of all vascular malformations, specifically because we have not observed thrombi formation in the treated vessels in the pig model.
All this evidence supports the use of bleomycin electroporation in the treatment of vascular malformations, also called bleomycin electrosclerotherapy (BEST). In principle, BEST could be a safe and effective approach for the treatment of vascular malformations; however, more clinical data are needed to confirm this approach. To date, there are only a handful of clinical reports on the treatment of vascular malformations with BEST. Finally, and importantly, the technique needs to be standardized through the development of dedicated standard operating procedures.
Publications on BEST are still limited in number. Table 2 summarizes the clinical studies and case reports published thus far.40,41,42,43,44,45 In summary, different types of vascular malformations have been treated, with favorable clinical outcomes. Most of the studies used intralesional bleomycin, either diluted or mixed with lidocaine. Bleomycin dosage varied between studies, but in most reports, it was lower than in traditional sclerotherapy. In addition, the number of treatments required was much lower when BEST was used than when bleomycin was used alone. Drug dosage, the number of treatments needed, and route of drug administration are all aspects that need to be explored to develop recommendations for the future use of BEST.
Clinical studies and case reports using bleomycin electrosclerotherapy40,41,42,43,44,45
McMorrow |
Venous malformation | 1 | Reduced dose: 1/3 of the standard dose | Not reported | Not reported | Considerable improvement after 6 unsuccessful sessions with bleomycin | Case report with poor respiratory function | |
Horbach |
Hypertrophic capillary malformations | 5 pts. (out of 20 planned) | 0.25 mg or units/cm3 | Plate & needle | Not reported | 7–8 weeks |
Randomized controlled pilot trial | |
Dalmady |
Lymphatic malformation | 1 | 0.5 mg/kg (5.4 mg) | Needle | 1st session: 68 applications |
63% growth-corrected volume decrease. |
Case report | |
Wohlgemuth |
Venous malformations | 17 pts. (20 lesions) | Calculated based on the size of the lesion. |
Needle & finger | Not reported | 3-month post-therapy Changes in volume MRI: Volume reduction,%: | ||
> 90% | 9 lesions | Retrospective observational case study | ||||||
> 70% in < 90% | 6 lesions | |||||||
> 50% in < 70% | 2 lesions | |||||||
< 35% | 2 lesions | |||||||
No response | 1 lesion | |||||||
Kostusiak |
Various vascular malformations | 30 pts. |
Calculated based on the size of the lesion. |
Needle & finger | Not reported | 17 Complete Response |
Prospective observational case study |
|
Krt |
Arteriovenous malformation | 1 | 750 IU BLM intralesional | Plate | 15 | CR 18 months after BEST | Case report |
AVM = arteriovenous malformation; BLM = bleomycin; CVM = capillary venous malformations; VM - venous malformation; LM = lymphatic malformation;
Another relevant aspect of BEST is the application of electric pulses. Due to the blood accumulated in the malformation, the electrical conductivity of the treated tissue is high. Therefore, it is assumed that the coverage of the target lesion with electric pulses does not need to be so strict as in electrochemotherapy. In this regard, some clinicians who perform BEST on patients report that fewer applications of electric pulses to the lesions are needed. This aspect that requires clarification in future studies.
Studies on BEST should also report the number and amplitudes of pulse applications and the electrical parameters (current). The predominantly used generator is from one producer, and varying electrodes specific to this generator are used. Usually, in each electric pulse application 8 pulses of 1000–1300 V/cm in frequency 5 kHz are applied. Since different electrodes are used for different clinical situations, the reports should describe which electrodes were used. Furthermore, when standard operating procedures for BEST will be prepared, recommendations for the use of specific types of electrodes should also be prepared.
To date, there are no standardized guidelines for BEST. As a result, each center applies the treatment according to local protocols and clinical experience. Therefore, standardization of some procedural aspects is needed.
The spread of a new technology depends on its
Currently, BEST must be practiced in the framework of clinical studies, where
It is expected that in the early stage of development, BEST will be considered in recurrences after previous treatments, whereas subsequently more precise indications for specific types of vascular malformations will be individuated.
Other relevant procedural aspects that need to be clarified include drug injection, questions of dosage, the need for general anesthesia, electrode placement and delivery of electric pulses.
Exclusion criteria need to be defined as well, such as pregnancy, lactation and allergy or hypersensitivity to bleomycin, or abnormal respiratory parameters.
The application of electric pulses, especially with needle electrodes, is painful. Therefore,
Another important issue is the
In electrochemotherapy, the
Another peculiar aspect is that the
The
Vascular malformations
BEST treatment can be performed as a day case procedure unless pain, bleeding or swelling is anticipated. Generally, follow-up is recommended at approximately three-month intervals.
These are recommendations and considerations for BEST treatment according to the experiences gained by the authors of this manuscript. The members of this working group will continue to share experiences and discuss results to identify the procedural aspects associated with the best results. When a more formal consensus is reached, we will propose our best practice in the form of standard operating procedures (SOPs).
InspECT is an international network of 42 clinical centers using electrochemotherapy for the treatment of cancer. This is the largest group of experts on electroporation-based treatments. Some of them are acquainted with BEST and report a positive experience as other external centers. Together, these centers form a network that can promote BEST worldwide. A dedicated working group for vascular malformations has been formed within InspECT. This group will promote clinical studies with BEST and seek collaboration with other centers. This paper aims to raise interest and awareness in the treatment of vascular malformations with BEST and provide an overview of the current status of development of this approach.
The number of clinicians using BEST to treat vascular malformations is growing. Due to the first and positive experiences in various vascular malformations, BEST application is being practiced in an increasing number of centers throughout Europe and the UK. This article summarizes the rationale and underlying mechanisms of BEST, along with the initial clinical experiences. Additionally, it highlights the main controversial procedural aspects and the need for dedicated SOPs.