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Neuroendocrine Tumors : Ki-67 Proliferation Index

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Ki-67 Labeling Index in Neuroendocrine Tumors of the GI Tract: At least 500 cells should be evaluated in hot-spots. Dark brown nuclear staining is considered positive. Cytoplasmic or weak nuclear staining is not counted.

Estimating Ki-67 labeling index by just eyeballing the slide is inaccurate and should be discouraged. Manual counting of positive cells in a printout of a high-quality photomicrograph is most accurate, reliable, and reproducible method. Ki-67 labeling index can be influenced by the antibody clone, different staining protocols used, and the section thickness.

In case of a discrepancy (seen in about one-third of cases) between the grades of mitotic count and Ki-67 labeling index (e.g. mitotic count <2/10 HPFs suggesting Grade 1 but Ki-67 labeling index of 3% or greater suggesting Grade 2, the higher grade should be used. Increased mitotic activity and a higher Ki-67 labeling index are associated with worse prognosis.

This photomicrograph shows scattered nuclear staining for Ki-67 in a neuroendocrine tumor of pancreas. Image courtesy of: Jian-Hua Qiao, MD, Los Angeles, California, USA. Used with permission.

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