Introduction

Cutaneous malignancies of the anal margin are rare, with squamous cell carcinoma (SCC) being the most common.1,2 Perianal SCCs present as a slow-growing perianal mass, often accompanied by pain and bleeding in a majority of patients.2 Due to its rarity and nonspecific clinical presentation, 70% to 80% of perianal SCCs are frequently misdiagnosed as other benign anorectal conditions, such as hemorrhoids.2 This leads to significant diagnostic delays and subsequent therapeutic challenges that negatively impact morbidity and mortality.2, 3, 4 Recognizing high-risk factors, such as immunosuppression and human papillomavirus (HPV), which together account for 86% to 97% of perianal SCCs, can lead to earlier diagnosis and improved outcomes.5 Other frequently reported risk factors include smoking and a history of sexually transmitted diseases.5,6 However, in the absence of these high-risk factors, it is important to consider other potentially underrecognized causes of perianal SCC, such as chronic inflammatory dermatoses.7, 8, 9

Perianal SCC secondary to chronic inflammation has been linked to several skin conditions, most notably hidradenitis suppurativa (HS), lichen sclerosus, and cutaneous Crohn’s disease.7, 8, 9, 10 Although SCC development has been well-documented in other psoriatic subtypes,11, 12, 13 no cases of perianal SCC arising in the setting of inverse psoriasis (IP) have been reported to date. Because inflammation-driven SCCs portend a worse prognosis, coupled with the inherent challenges in diagnosing perianal malignancies, it is important to recognize this rare, yet potentially fatal complication associated with untreated IP.13,14 Here, we present a rare case of advanced perianal SCC arising in chronically undertreated IP. This case highlights the importance of early and sustained management of IP, maintaining suspicion for malignancy in chronically inflamed perianal skin, and recognizing biopsy-related diagnostic challenges that may delay diagnosis of perianal SCC.8