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Primitive Neuroectodermal Tumor (PNET)

Primitive Neuroectodermal Tumor (PNET)

Primitive Neuroectodermal Tumor, also referred to as PNET, is a category of malignant (cancerous) tumors which appear similar under the microscope to medulloblastoma but occur primarily in the top part of the brain (the cerebrum). This category of tumors is molecularly and clinically diverse and includes the following diagnoses:

Pineoblastoma

  • CNS neuroblastoma with FOXR2 activation
  • CNS high-grade neuroepithelial tumor with BCOR alteration
  • CNS Ewing sarcoma family tumor with CIC alteration
  • CNS high-grade neuroepithelial tumor with MN1 alteration
  • CNS embryonal tumor not otherwise specified

Individually, each of these are very rare tumors.

Location

PNETs occur primarily in the cerebrum but can spread to other parts of the brain and spine.

Symptoms

Because they tend to be large tumors, symptoms are often due to increased pressure in the brain. These include headaches, morning vomiting, blurry vision, and behavioral changes, and seizures.

Treatment

Surgery is the standard initial treatment for these tumors. Because of their large size, tendency to spread, and extensive blood supply, total removal may not be possible at the time of diagnosis, and chemotherapy may be used to shrink the tumor to make surgical removal safer.

After surgery, treatment includes radiation to the brain and spinal cord (in children ages 3 and up at diagnosis) followed by chemotherapy. Radiation therapy is generally delayed in very young children due to the risks to the developing brain. For children diagnosed with PNET as infants or toddlers, chemotherapy is used alone after surgery.

Prognosis

Prognosis means a prediction of outcome. This information is usually based on information gathered from groups of people with the same disease. It is important to remember these statistics are not individualized.

In 2021, the PNET group of tumors began to be classified differently. Due to this change, prognostic data for PNET is limited.

Incidence

PNET are very rare tumors, accounting for about 100 tumors per year.

Age Distribution

PNET can occur in all ages, most commonly in childhood ages 0-14.

Risk Factors

Like many tumor types, the exact cause of PNET is not known. The risk of developing pineoblastoma is increased in patients with germline mutations in the RB1 or DICER1 genes.

Molecular Profile

Molecular profiling is the detection of specific genes, proteins, or other molecules in a tumor. This information helps confirm tumor diagnosis, inform treatment options, and predict prognosis.

Molecular analyses of the PNET group of tumors such as assessment for mutations or methylation analysis should be clinically performed to obtain a specific diagnosis for tumors in the PNET category in order to provide more specific prognostic information to the patient.  Molecular markers commonly found in the PNET group of tumors include FOXR2 activation, BCOR alteration, CIC alteration, and MN1.

Content last reviewed:

April 2022 by Holly B. Lindsay, MD, MS and Donald Williams (Will) Parsons, MD, PhD

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