International Consensus Guidelines for Diagnostic Criteria and Checklist for Future Studies for Minimally Invasive Carcinoma ex Pleomorphic Adenoma: An HN CLEAR Initiative

A variety of factors, including the extent of invasion, determine the clinical outcome in patients with carcinoma ex pleomorphic adenoma (Ca ex PA). A Head and Neck Consensus Language for Ease of Reproducibility (HN CLEAR) Steering Committee organized a working group (WG) to harmonize diagnostic and research approaches for assessing invasion in Ca ex PA. WG of head and neck pathologists and a radiation oncologist conducted 6 iterative rounds of online voting (Modified Delphi), using Google Forms, over an 8-month period on invasion in the setting of Ca ex PA. Agreement was defined by the same opinion of at least 50% of the responders. The list of parameters with predetermined options was developed. Minimally invasive Ca ex PA was defined as a pT1-2 pN0 carcinoma, resected en bloc with negative margins, with or without perineural invasion, without vascular invasion and without distant metastasis at presentation. Consensus was not reached on whether high grade histology is compatible with the concept of “minimal invasion”. Diagnosis of minimal invasion is possible when tumor excision is complete (with negative margins), en bloc (without fragmentation), and requires sampling of the entire tumor capsule or tumor-normal interface. The consensus guidelines characterizing Ca ex PA and the list of challenging aspects are provided. The WG proposed a checklist for future research, aiming to refine the diagnosis of in situ and minimally invasive Ca ex PA.