ORIGINAL RESEARCH Prevalence of Perineural Invasion in keratinocyte cancer in the general population and among organ transplant recipients Agnieszka Adams 1,2 | Nirmala Pandeya 2 | Brian De’Ambrosis 1,3,5 | Elsemieke Plasmeijer 2,4 | Ben Panizza 5 | Adele C Green 2,6 | Catherine M. Olsen 1,2 | David C. Whiteman 2 1 Faculty of Medicine, The University of Queensland, St Lucia, 2 QIMR Berghofer Medical Research Institute, Herston, 3 South East Dermatology, Annerley, 4 The Netherlands Cancer Institute, Amsterdam, 5 Princess Alexandra Hospital, Woolloongabba, Queensland, Australia, and 6 Manchester Academic Health Sciences Centre, CRUK Manchester Institute and University of Manchester, Manchester, UK ABSTRACT Background/Objectives: Basal cell carcinomas (BCCs) and cutaneous squamous cell carcinomas (SCCs) are the most commonly encountered cancers in fair-skinned populations worldwide. Perineural invasion is associated with worse outcomes for patients with BCC or SCC. Estimates of perineural invasion prevalence range widely, likely reflecting non-representative patient samples. We sought to determine the prevalence of perineural invasion in BCC and SCC in the general population, as well as among cancers arising in solid organ transplant recipients. Methods: We retrospectively analysed histopathol- ogy reports of BCC and SCC from patients enrolled in the QSkin Study (a population-based cohort of 43 794 Queensland residents recruited 2010–2011) and the Skin Tumours in Allograft Recipients (STAR) study (a cohort of 509 high-risk kidney or liver trans- plant recipients at the Princess Alexandra Hospital, Brisbane, recruited 2012–2014.) We estimated the prevalence of perineural invasion (and 95% confi- dence interval) in BCC and SCC, respectively, and identified clinical factors associated with perineural invasion. Results: In QSkin, we observed 35 instances of per- ineural invasion in 9850 histopathologically con- firmed BCCs (0.36%) and 9 instances of perineural invasion in 3982 confirmed SCC (0.23%) lesions. In the STAR cohort, we identified 4 lesions with per- ineural invasion in 692 BCCs (0.58%) and 16 reports of perineural invasion in 875 SCC lesions (1.9%). Conclusions: These data suggest that the overall prevalence of perineural invasion in keratinocyte cancer is low, although perineural invasion preva- lence may be slightly higher among organ transplant recipients when compared to the general population. Key words: immunosuppression, keratinocyte cancer, nonmelanoma skin cancer, perineural invasion, prevalence. INTRODUCTION Australia has a high incidence of keratinocyte cancers, which include basal cell carcinomas (BCCs) and cutaneous squamous cell carcinomas (SCCs). 1,2 Their cost of treat- ment is high in Australia, placing a heavy burden on the healthcare system. Recent analyses report that the total number of keratinocyte cancer treatments funded by Medi- care (Australia’s universal health insurance scheme) almost doubled between 1997 and 2010, with total costs for diagnosing and treating keratinocyte cancers reaching more than $500 million Australian dollars per year in 2010. 2,3 A proportion of keratinocyte cancers invade adjacent nerve sheaths, a phenomenon known as perineural inva- sion. Perineural invasion is a form of tumour dissemina- tion diagnosed when tumour cells are identified on histopathology as infiltrating any of the three layers of the Correspondence: Dr Agnieszka Adams, 11 Verney Road West, Graceville, Australia 4075. Email: nieshney@hotmail.com Agnieszka Adams, RACGP. Nirmala Pandeya, PhD. Brian De’Ambrosis, FACD. Elsemieke Plasmeijer, MD. Ben Panizza, FRACS. Adele C Green, FAFPHM. Catherine M. Olsen, PhD. David C. Whiteman, FAFPHM. Submitted 1 August 2019; revised 29 December 2019; accepted 12 January 2020. Australasian Journal of Dermatology (2020) , – doi: 10.1111/ajd.13247 © 2020 The Australasian College of Dermatologists