Abstract

Atypical squamous proliferation (ASP) presents a diagnostic challenge with broad differential diagnoses including reactive atypia associated with inflammation, benign neoplastic process, and squamous cell carcinoma (SCC). This diagnosis also poses a challenge for appropriate clinical management. We systematically reviewed clinical history and follow up of 218 patients with skin biopsies initially diagnosed as ASP. In our cohort 26% of patients were immunocompromised with history of multiple non-melanoma skin cancers. The follow up ranged from 3 to 201 months. Histologically, all biopsies demonstrated irregular squamous acanthosis with variable degree of cytologic atypia ranging from minimal to low-grade. Inflammatory infiltrate was frequently present. We divided all biopsies into 4 groups based on histopathologic impression: favoring carcinoma (22%), favoring reactive atypia (7%), favoring benign neoplasm (31%), and neutral (40%). 9 of 50 cases favoring carcinoma were further clinically pursued and subsequently confirmed as SCC. SCC was also subsequently identified in 10% of cases favored benign and 7% labelled neutral initially. Recurrences were present in only 2 patients with non-healing ulcer and immunocompromised status, respectively. No metastasis occurred in our entire cohort. For all cases confirmed as non-SCC, the conditions included long-term wound, infection, secondary change to chronic dermatitis and excoriation, lichenoid dermatitis, and autoimmune inflammatory disorders. In conclusion, ASP based on limited biopsy should be interpreted with caution clinically. Most SCCs need close clinical correlation, additional procedures, further ancillary studies, and follow-up for definitive diagnosis. Many reactive, inflammatory, and benign conditions show highly overlapping features with ASP preceding SCC diagnosis. Despite the disease heterogeneity, the overall risk of recurrence was low and there was no metastasis or disease related mortality in our cohort.

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