How are neuroendocrine tumors (NETs) of the lungs and thymus graded?

Updated: Dec 23, 2018
  • Author: Evan S Ong, MD, MS; more...
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However, for NETs of the lungs and thymus, the WHO includes only mitotic count and assessment of necrosis. [4] In its 2015 consensus statement on best practices for pulmonary neuroendocrine tumors, the ENETS noted that tumor grading based on a combination of KI-67, mitotic rate, and necrosis may be of clinical importance but lacks validation. [5]

Under the WHO grading scheme, pulmonary and thymic tumors fall into one of the following three grades [4] :

  • Low-grade tumors: < 2 mitoses/10 high power field (HPF) and no necrosis
  • Intermediate tumors: 2-10 mitoses/HPF and/or foci of necrosis
  • High grade tumors: >10 mitoses/10 HPF

The European Society for Medical Oncology (ESMO) uses only mitotic count for bronchial and thymic tumors for determining tumor grade, as follows [6] :

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

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