Human papillomavirus RNA in situ hybridisation in conjunctival papillary squamous cell carcinoma in situ

Background/aims Conjunctival papillary squamous cell carcinoma in situ (pSCCis) is an unusual type of conjunctival squamous cell carcinoma, which morphologically overlaps with squamous papilloma. The goal of this study was to characterise pSCCis clinically, histopathologically and with human papillomavirus (HPV) RNA in situ hybridisation (ISH) studies and to compare these findings with conjunctival papilloma. Methods HPV RNA ISH was performed on all pSCCis identified between 2015 and 2024. Clinical and histopathologic data were collected and compared with conjunctival papilloma cohort (2015–2024). Results 24 pSCCis (24 patients) were included. HPV RNA ISH studies identified high-risk HPV in 17 (71%), low-risk HPV in 5 (21%) and were negative in 2 (8%) lesions. Comparative analysis of high-risk HPV-positive conjunctival pSCCis with low-risk HPV-positive tumours showed that high-risk pSCCis were more likely to feature loss of goblet cells (76% vs 0%, p<0.01) with a well-defined transition between non-dysplastic and dysplastic epithelium (94% vs 0%, p<0.01). Clinically, intrinsic pigment was more common in low-risk HPV-positive lesions (18% vs 100%, p<0.01) with no other significant clinical, demographic, management and outcome differences between the two groups. When compared with high-risk HPV-positive pSCCs, low-risk HPV-positive lesions profiled closer demographically, clinically and histopathologically to 58 conjunctival papillomas (47 with histopathologic confirmation and low-risk HPV-positive status in all 7 tested lesions). Conclusions Conjunctival pSCCis phenotype is enriched for HPV (92%), with the predominant high-risk HPV-positive tumours (71%) showing the transformative phenotype and the low-risk HPV-positive tumours showing the productive phenotype morphologically and clinically overlapping with papilloma.