International Consensus Recommendations of Diagnostic Criteria and Terminologies for Extranodal Extension in Head and Neck Squamous Cell Carcinoma: An HN CLEAR Initiative (Update 1)

Purpose: Extranodal extension (ENE) increases the risk of recurrence and death in head and neck squamous cell carcinoma (HNSCC) patients and is an indication for treatment escalation. Histopathology forms the mainstay of diagnosing ENE. There is substantial variation in the diagnosis of ENE and related terminology. Harmonising the diagnostic criteria for ENE was identified as a priority by the Head and Neck Consensus Language for Ease of Reproducibility (HN CLEAR) Steering Committee and its global stakeholders. Methods: An international working group including 16 head and neck pathologists from eight countries across five continents evaluated whole slide images of haematoxylin and eosin-stained sections depicting potential diagnostic problems through nine virtual meetings to develop consensus guidelines. Results: ENE should be diagnosed only when viable carcinoma extends through the primary lymph node (LN) capsule and directly interacts with the extranodal host environment with or without desmoplastic stromal response. Identifying the original LN capsule and reconstruction of its contour can assist in the detection and assessment of ENE. The term matting is recommended for confluence of two or more nodes due to histologically identifiable tumour extending from one LN to another. Matting constitutes major form of ENE. On the other hand, the terms fusion/adhesion/confluence/conglomeration and other synonyms of adhesion should be limited to confluence due to fibrosis or inflammation without histologically identifiable tumour between involved lymph nodes. Tumour extension along narrow needle tracks or spillage of cyst contents following an FNA do not constitute ENE. Conclusions: The consensus recommendations encompassing the definition of ENE, macroscopic and histologic examination of lymph nodes (LN) and practical guidelines for handling challenging cases are provided.