Spatial evidence for <i>carcinoma</i> in situ ( <scp>CIS</scp> ) as an entity in human papillomavirus ( <scp>HPV</scp> )‐associated tonsillar squamous cell carcinoma ( <scp>TSCC</scp> )

Human papillomavirus (HPV)-associated tonsillar squamous cell carcinoma (TSCC) is suggested to arise in tonsillar crypts. It also constitutes a rare exception in the literature of carcinoma development, as carcinoma in situ (CIS) is not a recognized entity and dysplastic stages are not evident. Here we investigated the evidence of this. Hence, a systematic review and meta-analysis was performed to study tumor origin. MEDLINE was searched and all original studies reporting tumor origin in HPV-associated oropharyngeal cancer were included. We also used spatial transcriptomics (10× Visium) on HPV-associated TSCC, cervical, and HPV-independent oral cancer cases. We compared tonsillar CIS to cervical high-grade intraepithelial lesion (HSIL). We studied epithelial cell gene expression across the sample types and epithelial cellular states. A trajectory analysis was performed in HPV-associated tumors. In total, 14% of all TSCC were of surface origin in the systematic review. Spatial transcriptomics revealed that tonsillar CIS and HSIL clustered with a high correlation when using a pseudo-bulk approach. Moreover, when all epithelial cells were analyzed unsupervised, ten epithelial cell clusters that correlated to histology were identified. Two of these clusters were dysplastic and occurred in all samples. A sequential progression from dysplasia to invasion was observed in both TSCC and cervical cancer in the trajectory analysis. We conclude that a subset of HPV-associated TSCC may arise from the surface and that there is a sequential progression toward invasive disease in HPV-associated TSCC, similar to that of cervical cancer. The findings suggest that pure tonsillar dysplastic lesions should hypothetically exist.