Laryngeal Squamous Cell Carcinomas are Commonly Associated With Differentiated Squamous Intraepithelial Neoplasia With or Without an Admixture With Usual Type of Squamous Intraepithelial Neoplasia: Clinical and Pathologic Significance.

Background: Differentiated squamous intraepithelial neoplasia (dSIN) is a pathway in the development of invasive squamous cell carcinoma (SCC) distinct from the usual-type squamous intraepithelial neoplasia (uSIN) and has not been described in the larynx.

Materials And Methods: Sixty-nine consecutive cases of SCC were identified which included 25 dSIN, 13 uSIN, and 31 mixed dSIN+usual-like SIN (u-like SIN) cases.

Results: dSIN was characterized by atypical squamous cells limited to the basal/parabasal layers and u-like SIN was characterized by cytologic atypia limited to less than full thickness. Despite the lack of neoplastic involvement of the full thickness of the epithelium, these types of SIN were commonly connected with invasive carcinoma. Prior biopsies demonstrating only dSIN, without the underlying invasive SCC, were underdiagnosed in 2 cases. Because of the frequent keratinization, u-like SIN likely represents the "keratinized dysplasia" and shows changes suggestive of dSIN with upward spread of neoplastic cells into the upper layer of the epithelium.

Conclusions: Laryngeal dSIN represents an important but under recognized pathway of invasive SCC development. As moderate dysplasia of uSIN type are not associated with invasive SCC, labeling u-like SIN as dysplasia of grade 2 or 3 likely leads to the controversies in the current grading systems in the upper aerodigestive system and causes confusion for clinicians.