Ablation and Embolization for Pancreatic Cancer

Ablation and embolization are minimally invasive treatments that destroy tumors without surgical removal. They are sometimes used to treat pancreatic cancer that has spread to other organs, especially the liver. They can also help in the treatment of pancreatic neuroendocrine tumors (NETs) that have not spread but cannot be removed with surgery or in patients who are felt to be too high risk for surgery.

While they may not cure the cancer, ablation and embolization can help control tumor growth and alleviate symptoms. They are typically used in conjunction with other kinds of pancreatic cancer treatment such as chemotherapy or immunotherapy.

Ablation uses chemicals, extreme heat or cold to kill cancer cells. It is most suitable for tumors less than 2 cm in diameter. For small tumors, several studies show ablation is as good as surgical resection.

Regardless of the type of ablation therapy, your doctor will use an imaging technique, such as a computed tomography (CT) scan or ultrasound, to locate and guide the insertion of a needle probe into the tumor. These probes are connected via cords to a generator that supplies heat or cold. In some cases, absolute alcohol or some other agent may be injected directly into the tumor.

There are a few types of ablation techniques: radiofrequency ablation, microwave ablation and cryotherapy.

Radiofrequency ablation

Radiofrequency ablation (RFA) is a minimally invasive procedure where metal prongs that project out from the needle’s hollow core penetrate the tumor. Subsequently, high-energy radio waves are passed through the needle to its tip and prongs. This creates an l area of heat that kills the cancer cells (a process called coagulative necrosis) and closes small blood vessels, which lowers the risk of bleeding. The dead tumor cells are ultimately replaced by scar tissue. Over time, the scar tissue may involute (shrink and disappear).

Microwave ablation

Microwave ablation (MWA) works in a similar way to RFA, but instead of radio waves, microwaves are transmitted through the probe. This generates heat that burns the tumor and destroys the cancer cells. It can also make the tumor more sensitive to the effects of radiation and some anti-cancer drugs.

Cryotherapy

Cryotherapy (or cryoablation) uses extremely cold temperatures to destroy cancerous tissue. More specifically, argon or nitrogen gas is pumped into the needle probe. This brings the temperature of the tumor to extremely low levels, freezing and destroying the tumor. Cryotherapy may work better for larger tumors than other ablation techniques.

Embolization involves the injection of substances directly into an artery to stop or reduce the blood supply to a tumor. This starves the tumor of oxygen and nutrients, thereby destroying the cancer cells.

Embolization is typically used for larger tumors (up to 5 cm across) that have spread from the pancreas to the liver or are too numerous for surgical removal or ablation. Lesions within the pancreas itself are not amenable to embolization since there is a very limited blood supply to the primary cancer.

There are a few types of embolization: transarterial embolization, chemoembolization and radioembolization.

Transarterial embolization (TAE)

During this procedure, a thin, flexible tube called a catheter is inserted into an artery through a small cut in the inner thigh or wrist and threaded into the hepatic artery. Contrast dye injected into the bloodstream is used to observe the path of the catheter via X-ray and guide its insertion into the hepatic artery.

Once the catheter is in place, nanoparticles composed of gelatin sponges or glass beads are injected into the artery directly. These substances, called embolic agents, block the blood supply to the tumor and kill the cancer cells, leading to shrinkage or necrosis of the tumor. Afterwards, the catheter is withdrawn and the entry site cleaned and covered with a dressing.

Some embolic agents are designed to gradually break down and/or be absorbed by your body. Others, especially those that are not biodegradable or bioresorbable, may remain in the treated area. Known as permanent embolics, these agents can become encapsulated by scar tissue, incorporated into nearby tissues or carried away to smaller vessels where they become lodged.

The use of permanent embolics in TAE is generally considered safe and effective when performed by trained and experienced interventional radiologists. However, as with any medical procedure, there are potential risks and complications associated with TAE using permanent embolics. These include:

• Ischemia: If the embolization is too extensive, it could potentially lead to damage of surrounding healthy liver tissue.
• Reperfusion injury: In some cases of TAE, after the catheter is removed, blood flow may be restored to previously ischemic tissue. This can lead to inflammation and additional tissue damage, known as reperfusion injury. In severe cases, tachycardia (increased heart rate) and hypotension (low blood pressure) can occur.
• Non-target embolization: There is a risk of embolic material traveling to other areas and causing blockages in vessels that are not intended for treatment. This could potentially affect healthy liver tissue and liver function.

More common side effects are pain and nausea after the treatment, which is usually self-limited. Therefore, it is vital that you discuss the potential risks and benefits of TAE with your doctors before opting for the procedure.

Transarterial chemoembolization (TACE)

This embolization technique combines TAE with chemotherapy. It is usually done by delivering chemotherapy through the catheter and directly into the artery, just before it is plugged with an embolic agent.

Besides stopping the tumor’s blood supply, this procedure delivers a very high concentration of chemotherapeutic agents to the tumor, which can destroy the cancer cells directly. The injection of embolic agents also traps the chemotherapeutics in the tumor for several weeks, allowing their cancer-killing effects to last for a prolonged period of time. Since the therapy is delivered solely to the tumor and does not travel through your bloodstream, the occurrence of chemotherapy side effects is avoided.

A specific type of TACE called drug-eluting bead chemoembolization (DEB-TACE) uses tiny beads or microspheres that contain chemotherapy drugs, whose gradual release can kill the cancer cells.

Mitomycin C, cisplatin, irinotecan and doxorubicin are the most common chemotherapy drugs used for TACE or DEB-TACE.

Transarterial radioembolization (TARE)

This procedure combines embolization and radiotherapy. Tiny radioactive beads or microspheres attached with a radioactive isotope (yttrium-90) are injected into the hepatic artery.

TARE is microembolic and does not reduce blood flow to the tumor. The continued blood supply provides oxygenation of the tissue to allow free radical formation, which is needed for the radiation effects. This essentially delivers a high dose of radiation directly to the tumor in the liver, thereby destroying the cancer cells.

The effect of the radiation lasts for several days and is mostly limited to the tumor site, as it radiates less than half an inch into adjacent tissues. In this way, TARE is a targeted form of treatment that limits the amount of the liver exposed to radiation, sparing healthy liver tissue and other surrounding organs from unnecessary exposure.

Ablation and embolization are typically outpatient procedures where you go home on the same day. While the time taken for the procedure depends on the specific technique used, the tumor’s size, and other factors, it usually lasts one to three hours.

This form of treatment can be done under general anesthesia (where you are in a deep sleep so you do not feel any pain) or with conscious sedation (where you are awake, but sleepy and should not experience any pain). If general anesthesia is needed or if you experience pain or nausea after the procedure, you might have a night’s stay in the hospital.

The area of your skin through which the needle or catheter is inserted is numbed with local anesthetic. At the end, your radiologist removes the needle probe and applies pressure to stop any bleeding. The opening in the skin is then covered with a dressing.

Recovery afterwards can take up to six weeks. The most common side effect is fatigue. Other less common side effects and complications include:

• Abdominal discomfort or pain at the entry site
• Flu-like symptoms such as fever, body aches and feeling sick (collectively known as post-ablation or post-embolization syndrome)
• Nausea and/or vomiting
• Liver infection
• Blood clots in the blood vessels surrounding the liver
• Collection of pus in the region where the tumor was removed (known as a liver abscess)
• Bleeding
• Damage to nearby organs (e.g. diaphragm, bile ducts) which may need surgical correction

You will be provided with painkillers and anti-sickness medication to manage some of the side effects. If these problems grow more severe or if they do not resolve, do inform your doctor(s).

Follow-up imaging tests, such as CT or magnetic resonance imaging (MRI) scans, will be performed to examine how well the treatment worked and to monitor the treated tissues.