Pathologic Classification of Neuroendocrine Tumors

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At the time of diagnosis, it is essential to ascertain the grade for neuroendocrine tumors (NETs), since response in high-grade disease is substantially inferior, notes Rodney F. Pommier, MD. This can be accomplished using mitotic counts and the Ki-67 proliferation marker. In general, a mitotic count less than 10 is characterized as low grade, between 10 and 20 is considered intermediate grade, and greater than 20 is indicated as a high-grade tumor. In general, patients with high-grade tumors receive treatment with platinum-based chemotherapy.

In addition to markers, pathologists examine cellular differentiation, suggests Diane Reidy-Lagunes, MD, MS. For well-differentiated tumors, the Ki-67 or mitotic counts are utilized to further determine the correct grade. Traditionally, a Ki-67 above 20% indicated a high-grade tumor. However, recent data suggest that a Ki-67 greater than 55% may be a more accurate indicator of poor prognosis, Reidy-Lagunes notes.

Panelists agree these classification systems have not yet been perfected. To adjust for this, Matthew H. Kulke, MD, suggests a certain degree of clinical judgment is needed to determine whether a patient is a good candidate for platinum-based therapy. To help with this process, Reidy-Lagunes recommends utilizing an octreotide scan. If positive, patients with a high Ki-67 do not usually respond to platinum-based therapy.