How are carcinoid tumors graded?

Updated: Feb 12, 2019
  • Author: Cameron K Tebbi, MD; Chief Editor: Max J Coppes, MD, PhD, MBA  more...
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Grading schemes for neuroendocrine tumors (NETs) use mitotic count; the level of the nuclear protein Ki-67, which is associated with cellular proliferation; and assessment of necrosis. The World Health Organization (WHO) and the European Neuroendocrine Tumor Society (ENETS) both incorporate mitotic count and Ki-67 proliferation for the classification of gastroenteropancreatic NETs (GEP-NETs). [97, 98, 99]

Tumors fall into one of the following three grades:

  • G1: well differentiated, low grade
  • G2: well differentiated, intermediate grade
  • G3: poorly differentiated, high grade

However, for NETs of the lungs and thymus, the WHO includes only mitotic count and assessment of necrosis. [100] In its 2015 consensus statement on best practices for pulmonary neuroendocrine tumors, the European Neuroendocrine Tumor Society (ENETS) noted that tumor grading based on a combination of KI-67, mitotic rate, and necrosis may be of clinical importance but lacks validation. [101]

Under the WHO grading scheme, pulmonary and thymic tumors fall into one of the following three grades [100] :

  • Low-grade tumors:  
  • Intermediate tumors:  2-10 mitoses/HPF and/or foci of necrosis
  • High grade tumors:  >10 mitoses/10 HPF
  • </ul>

    The European Society for Medical Oncology (ESMO) uses only mitotic count for bronchial and thymic tumors to determining tumor grade as follows [102] :

    • Low-grade tumors:  
    • Intermediate tumors:  10-20 mitoses/10 HPF
    • High grade tumors:  >20 mitoses/10 HPF
    • </ul>

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