Tuesday, May 15, 2012

Primitive Neuroectodermal Tumors of the Soft Tissue or Bone

Primitive neuroectodermal tumors or PNET are very rare group of tumors that are highly malignant. In clinical manifestation these tumors exhibit great diversity. They manifest in the bone and soft tissue. Pathologist find them very difficult to distinguish because they have similarities to other small, round tumors.

                                                    PNET tumors under a microscan

PNET tumors are classified into three groups.

I. CNS primitive neuroectodermal tumors (PNETs) - Tumors derived from the central nervous system

II. Neuroblastoma - Tumors derived from the autonomic nervous system

III.Peripheral primitive neuroectodermal tumors (pPNETs) - Tumors derived from tissues outside the central and autonomic nervous system

This cancer is usually seen in children and adolescents and is very fast growing and can quickly metastasize to other organs.

Peripheral primitive neuroectodermal tumors (pPNETs) are also classified as part of the Ewing family of tumors (EFTs); peripheral primitive neuroectodermal tumors (pPNETs) and Ewing family of tumors (EFTs) are often referred to interchangeably in the literature. Generally, Ewing family of tumors (EFTs) and peripheral primitive neuroectodermal tumors (pPNETs) represent different manifestations of the same tumor and have similar genetic alterations. Ewing sarcoma, however, is more common in bone, while peripheral primitive neuroectodermal tumors (pPNETs) are more common in soft tissues. Immunohistochemical and cytogenetic studies suggest that these tumors all have a common origin.

Tissue biopsy with cytogenetic and immunohistochemical studies is paramount in diagnosing peripheral primitive neuroectodermal tumors (pPNETs). Radiologic studies such as CT scans and MRI are essential in determining the limits of tumor involvement and ruling out metastatic disease. On CT scans, peripheral primitive neuroectodermal tumors (pPNETs) appear as heterogeneous masses, often invading surrounding tissues, including bone. MRI reveals a mass isointense to muscle on T1-weighted images, while hyperintense on T2-weighted image 

Due to the fact that PNET is metastatic then full body scans need to be performed to see the extent of the tumor growth. 

Treatment Plan

Chemotherapy and radiation are necessary adjuncts in the treatment of primitive neuroectodermal tumors (PNETs). Chemotherapy regimens have significantly improved outcomes in patients with peripheral primitive neuroectodermal tumors (pPNETs). The treatment paradigms differ based on whether the disease is localized or metastatic. As would be expected, the treatments for peripheral primitive neuroectodermal tumors (pPNETs) and Ewing family of tumors (EFTs) are similar in terms of chemotherapeutic regimens.
Current recommendations advocate complete surgical resection whenever possible, adjuvant versus neoadjuvant chemotherapy, and radiotherapy. Multimodality treatment is advocated to prevent metastatic disease, recurrent disease, and to treat residual tumor after resection. Carvajal and Meyers, in a comprehensive review of the chemotherapeutic regimens in the treatment of PNETs and Ewing family of
 tumors (EFTs), recommend a regimen that includes vincristine, doxorubicin, and cyclophosphamide with ifosfamide and etoposide.
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