Impaired vocal cord mobility due to thyroarytenoid muscle involvement predicts poorer prognosis in T2 glottic cancer. Opportunity for refinement of the TNM 8th Edition

Thyroarytenoid muscle (TAM) invasion by glottic cancer marks an intermediate step of tumour progression from T1 (purely involving the vocal ligament) to T3 (invading the paraglottic space). From a functional point of view, this event is clinically manifested by impaired vocal cord mobility (cT2) that, when present, is associated with a decrease in oncologic outcomes compared to cT2 with purely superficial supra- and/or subglottic extension with normal cord mobility. Even though this fact has been well-recognised over the years with supporting data from both surgical and nonsurgical series, no subcategorisation has ever been officially attempted due to the fact that vocal cord mobility assessment is a highly subjective parameter on fibreoptic videoendoscopy. However, recent progress has been made in the objective assessment of TAM invasion, both radiologically (by computed tomography and magnetic resonance) and on histopathologic examination (by measuring the tumour depth of invasion). This review aims to examine the evidence in favour of classifying T2 glottic cancers based on TAM involvement into 2 distinct subcategories (T2a vs T2b) consequent to advances in contemporary objective assessment options.