Kaposiform Hemangioendothelioma (KHE)

What are the symptoms of KHE?

The exact symptoms of KHE depend on where the lesion appears. The most common symptom of KHE is a growing lesion on the skin. This lesion:

• is usually a deep reddish-purple and has poorly defined edges
• is firm and warm to the touch
• often has shiny and tense skin
• may be accompanied by a bruise-like discoloration nearby, or tiny red or purple spots (petechiae) anywhere on the body
• sometimes swells and becomes painful, or causes pain with movement or reduced range of motion

The exact symptoms of KHE depend on where the lesion appears. About 10 percent of children with KHE have no skin lesion, and some lesions penetrate deeper than the skin into other tissues.

Most children have few complications and may not need medical therapy. Some patients with KHE, however, develop what is called Kasabach-Merritt phenomenon (KMP), in which their tumor traps platelets and keeps them from circulating through the bloodstream. Because platelets help prevent bleeding, patients with KMP have a higher risk of bleeding.

KMP may develop in patients whose tumors are larger, invade into deeper tissues, or if there are sites of infection or inflammation nearby. Some children who develop KMP also lack other blood proteins that help control bleeding, such as fibrinogen.

What causes kaposiform hemangioendothelioma?

Researchers are still searching for the cause of KHE. It is not inherited, and while it typically occurs in infancy, KHE can arise prenatally or in adults after trauma.

How is kaposiform hemangioendothelioma diagnosed?

The first step in treating your child is forming an accurate and complete diagnosis. An experienced vascular anomalies specialist can help tell the difference between KHE and other vascular anomalies.

Most often, KHE is diagnosed through a complete medical history, a thorough physical exam and one or more of the following tests:

• complete blood count
• magnetic resonance imaging (MRI)
• ultrasound
• biopsy

What are the treatments for kaposiform hemangioendothelioma?

Some mild KHE tumors go away without treatment. For those that do not, doctors have multiple treatment options available to them, depending on the size, location, and behavior of the tumor. The goals of treatment are to relieve symptoms, shrink the tumor, and reverse Kasabach-Merritt, if it is present.

Treatment options include:

• Watchful waiting: For superficial tumors without low platelets, your child’s doctor may want to observe the tumor for a few months before determining the most appropriate treatment.
• Oral or topical steroids: In mild cases, oral or topical steroids may help other treatments work better and improve superficial lesions. However, only about 12 percent of KHE tumors respond to steroids.
• Drug therapy: Considered the gold standard treatment for most tumors, medications slow the growth of the tumor and improve symptoms.
• Surgery: Your doctor will only recommend surgery if your child’s tumor is very small or extremely aggressive and able to be completely removed.
• Embolization: This minimally invasive procedure blocks the main artery feeding a KHE tumor to cut off the blood supply and shrink it. We do not attempt embolization in cases where several arteries feed into the tumor, which is often the case with KHE.

Medications

Medications used to treat KHE include:

• Sirolimus: Also known as rapamycin, this oral medication suppresses the immune system and slows the growth of abnormal lymphatic vessels that form the tumor. It has been found to shrink KHE tumors and improve symptoms, including pain.
• Vincristine: This chemotherapy drug targets all dividing cells within the body and is therefore used to treat many cancers. While KHE is not a cancer, there are dividing cells in the tumor. Vincristine has been used successfully for decades to treat KHE.

What is the long-term outlook for a child with kaposiform hemangioendothelioma?

Many patients have an excellent long-term outlook through successful KHE treatment. In general, you child's prognosis depends on:

• how quickly the diagnosis is made and appropriate medical therapy is started
• the size, location, and extent of disease
• the tumor's initial response to therapy

When KHE is suspected, it’s important to see a specialist quickly to allow early discussions about treatment. Specialists can then attempt to shrink the tumor before it affects muscles or other tissues nearby. Early treatment could also help reduce long-term complications by preventing further growth.

How we care for KHE

Because kaposiform hemangioendotheliomas are so rare, very few doctors have experience diagnosing and treating them. The Vascular Anomalies Center (VAC) at Boston Children's Hospital has evaluated more children with KHE than any other hospital in the world. The VAC's 25 physicians — representing 16 medical and surgical specialties — draw on those experiences to redefine the best therapies and achieve better long-term outcomes for children with KHE.

Our areas of innovation for kaposiform hemangioendothelioma

Physicians and researchers at the VAC have generated an extensive database of cases of vascular anomalies, including more than 250 cases of KHE. We are actively evaluating the best therapies for KHE and studying long- term outcomes after KHE. As our database grows, it will help shine more light on this rare and often misunderstood condition.

In 2015, we opened a clinical trial comparing vincristine and sirolimus in patients with KHE complicated by KMP. This randomized, controlled, multicenter trial involving several institutions around the country will answer questions about which of these medications is a better treatment for KHE.