Primitive neuroectodermal tumors (PNET) : Causes, Symptoms & Treatments

What exactly are PNET? Are they the same as medulloblastomas?

Yes and no. Under a microscope, PNET tumors appear to be similar to a tumor called medulloblastoma, and some will classify medulloblastoma as “PNET (cerebellum).” However, it has been demonstrated that medulloblastomas behave differently than PNET in other locations in the brain.

According to the World Health Organization (WHO), all undifferentiated tumors—regardless of location—are derived from common cells and are therefore classified as PNET. To differentiate, their location is frequently indicated in parentheses. This separates medulloblastoma (PNET cerebellum) and pineoblastoma (PNET in the pineal region) from other PNET such as PNET in the supratentorial compartment (meaning occurring in the cerebrum) or in the spine.

What causes a PNET?

Researchers have not been able to find an identifiable cause or risk factors for PNET. There doesn’t appear to be a genetic predisposition, meaning the disease does not seem to run in families.

What are the symptoms of a PNET?

The symptoms of a PNET depend on the location of the tumor, and each child may experience symptoms differently. Symptoms of a PNET in the supratentorial compartment usually arise quickly and last up to several weeks. These tumors are often seen in the older child or teenager.

Some common symptoms occur due to increased pressure within the brain, including:

headache (generally upon awakening in the morning)
vomiting
fatigue/lethargy
seizures

Pineoblastomas (PNET in the pineal region, a tiny organ near the center of the brain) are usually seen in young children. Common symptoms may include increased pressure in the brain, resulting in:

headache (generally upon awakening in the morning)
vomiting
fatigue/lethargy
eye movement problems and/or complaints of double vision, since the tumor is close to the nuclei (centers in the brain) that regulate eye movements and coordination

Symptoms of PNET of the spine may include:

back and/or leg pain
slow development of weakness in the legs
impairment of bowel and/or bladder function, including incontinence

The symptoms of a PNET may resemble other conditions or medical problems. Always consult your child’s physician for a diagnosis.

What are the treatments for PNET?

Specific treatment for PNET will be determined by your child’s physician based on:

your child’s age, overall health and medical history
type, location, and size of the tumor
extent of the disease
your child’s tolerance for specific medications, procedures or therapies
how your child’s doctors expects the disease to progress
your opinion or preference

Treatment may include (alone or in combination):

surgery– first to obtain a biopsy for diagnosis and to remove the tumor. The surgeons will try to get as much as the tumor out as possible, since aggressive tumor removal is associated with better long-term outcome. Removing the whole tumor is usually possible in the supratentorial tumors, but less frequently accomplished in the tumors of the pineal region and rarely in the spine.
radiation therapy– if your child’s tumors have been incompletely removed or if they recur, radiation therapy may be recommended. This type of therapy uses high-energy rays (radiation) from a specialized machine to kill cancer cells and shrink tumors. Usually, the radiation therapy is delivered first, followed by the chemotherapy. In infants, or children under the age of 3, radiation therapy is withheld.
chemotherapy- a drug treatment that works by interfering with the cancer cell’s ability to grow or reproduce
ventriculoperitoneal shunt (also called a VP shunt)– a bypass, usually a type of tubing, that is placed in the head to drain excess cerebrospinal fluid (CSF) from inside the brain to space in the abdomen. A VP shunt helps control the pressure inside the brain.

If there is hydrocephalus (swelling of the brain) in a pineoblastoma, another procedure called an ETV (endoscopic third ventriculostomy) may be necessary. There have been reports of these tumors traveling through shunts into the peritoneal cavity; therefore, all efforts are made to avoid placement of a shunt in these children.

How is chemotherapy given?

Different chemotherapies may be given:

as a pill to swallow
as an injection into the muscle or fat tissue
intravenously (directly to the bloodstream, also called IV)
intrathecally (directly into the spinal column with a needle)

How is chemotherapy used?

This depends on many factors. Some things to keep in mind:

A number of combinations of chemotherapy drugs are currently being used to stabilize and, in some cases, to shrink the size of the tumor.
Depending on the type of cancer, chemotherapy drugs may be given in a specific order.
Chemotherapy may be used alone for some types of cancer, or in conjunction with other therapy such as radiation or surgery.

Does chemotherapy come with bad side effects?

While chemotherapy can be quite effective in treating certain cancers, the agents do not differentiate normal healthy cells from cancer cells. Because of this, there can be many adverse side effects during treatment. Being able to anticipate these side effects can help your child, family and your child’s health care team prepare for and sometimes prevent these symptoms from occurring.

How are side effects managed?

The side effects of therapy will depend on the surgery and other treatments that have been performed, including radiation therapy to the brain and spine.

Treatment for these side effects may include physical and occupational therapy (if your child experiences weakness or sensory loss), and speech therapy (if her speech is impaired), all on either an inpatient or outpatient basis.

What is the expected outcome after treatment for PNET?

Since these tumors are so rare and hard to classify, it’s difficult to analyze outcome and survival rates. The overall 5-year survival of patients with PNET is between 50 and 60 percent, but is clearly worse among infants and pineoblastoma patients with incomplete tumor removal or poor response to radiation therapy.

What about progressive or recurrent disease?

Relapsed PNET is almost always fatal and there are no good chemotherapy or other curative therapies available. There are trials looking at bone marrow transplantation with aggressive chemotherapy and use of novel biologic agents, but most of these are currently experimental.

What is the latest research on PNET?

A variety of chemotherapeutic regimens have been evaluated in the treatment of newly diagnosed high-grade gliomas.

While studies in adults have suggested that procarbazine, vincristine and CCNU (PVC) produce modest responses in grade III gliomas, this has not been demonstrated for pediatric cases or for grade IV tumors.
Several other regimens have also produced responses, but none has improved survival.
Increased doses of chemotherapy in the setting of autologous bone marrow transplant have also not produced notable advantage.

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