270 Radiologic diagnosis of Extranodal Extension (ENE) in patients with HPV-positive oropharyngeal cancer: consensus diagnosis and influence on prognosis

Abstract

Tumor often progresses through the weakest part of any surrounding tissues. The extent of tumor invasion depends on: a. Aggressiveness of the tumor cells (e.g. number and invasive character of stem cells), b. robustness of the surrounding tissues and their composition (e.g. vessels), and c. time to allow the tumor to proliferate. The lymph node (LN) capsule comprises dense connective tissue stroma and collagenous fibers, and is a natural barrier that generally prevents further tumor progression. Permeation of tumor through the nodal capsule into surrounding tissues is termed “extranodal extension”. The idiosyncratic and inconsistent mechanism of ENE is imprecisely understood, but it is thought to be due to either tumor cell proliferation that outpaces the capacity of nodal capsular expansion (“ruptures” the LN capsule), or factors within the tumor or tumor microenvironment that facilitate the “breach” of the capsule. The latter might explain ENE in small LNs, or a “neglected” tumor (lengthy intranodal tumor growth with eventual “rupture” through an expanded nodal capsule). Several biomarkers (e.g. podoplanin) that are often associated with tumor aggressiveness have been reported to have a high expression in ENE+ LN. ENE represents a spectrum of tumor nodal invasion. The early sign of ENE can only be visible under the microscope (pathologic ENE); when ENE progresses further, the radiographic signal changes become apparent, making it visible on imaging (iENE). Most advanced ENE causes emergence of clinical surrogates (e.g. peau d'orange, or a “fixed” nodal mass), rendering it detectable by regular clinical examination (ENEc). iENE has been reported to be one of the strongest anatomic prognostic factors for overall survival (mainly due to increased risk of distant metastasis) in HPV-positive oropharyngeal carcinoma (HPV+ OPC), and is able to identify a subgroup of stage I disease with poor prognosis. Several deintensification trials (NRG-HN002, ORATOR, ORATOR2, E3311) have excluded HPV+ OPC with some form of iENE from trial enrolment. Several authors have proposed that iENE be included in future clinical N classification for HPV+ OPC. However, adoption of iENE in clinical care remains challenging because it is not a well-defined radiologic feature among the radiology community. Various definitions / descriptions of iENE have been used in literature. There is also insufficient awareness of the prognostic importance of this parameter in head and neck oncology community. The international iENE Expert Panel was convened under the HNCIG comprised expert internationally renowned neuroradiologists and clinicians. Several rounds of Delphi process were conducted to consolidate iENE definition. The consensus recommendations on the terminology and diagnostic criteria for iENE were generated. The experts in the consensus process recognized the following as criteria for the diagnosis of iENE: clear evidence of irregular or indistinct nodal margin/border; extension into perinodal fat; extension into adjacent structures, and conglomerate/matted/coalescent nodes. These recommendations have been endorsed by 19 national organisations, representing 34 countries. With increased awareness and consolidated definition as well as training, iENE could become an important baseline factor for risk stratification and staging in HPV+ OPC.