CPC08 Utility of p53 immunohistochemistry in atypical fibroxanthoma and pleomorphic dermal sarcoma: a retrospective study of 50 cases

Abstract

Atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) are uncommon cutaneous neoplasms arising on chronically sun-damaged skin. They share similar clinical and histopathological features, with PDS distinguished by adverse histological criteria and metastatic potential. Both are diagnoses of exclusion and lack specific immunohistochemical markers, making diagnosis challenging, particularly in small biopsies or re-excision specimens. While TP53 alterations are well evidenced at the molecular level, the practical utility of p53 immunohistochemistry for diagnosis has received limited emphasis. We conducted a retrospective review of 50 specimens from 43 patients diagnosed with AFX or PDS over a 5-year period at a single district general hospital. Clinical data included age, sex, anatomical site and tumour size. p53 immunohistochemistry was assessed retrospectively for nuclear staining pattern and categorized as aberrant overexpression, aberrant null or wildtype. Additionally, we included re-­excision specimens in which there were additional challenges of distinguishing residual tumour from surgical scarring, as well as examples of local recurrence and metastasis. Aberrant p53 expression was identified in 92% of specimens, most commonly as diffuse nuclear overexpression. Compared with CD10, the p53 nuclear staining pattern readily assists in identifying subtle tumour extension and is particularly helpful in identifying residual tumour from scar tissue in re-excisions. Concordant p53 staining between primary, residual or recurrent tumours increased diagnostic confidence and assisted in margin assessment. Although nonspecific, p53 immunohistochemistry is a useful adjunct to exclude diagnoses such as spindle cell squamous cell carcinoma and melanoma. Particularly, aberrant p53 confirmed AFX/PDS in tumours showing relatively mild cytological atypia and low mitotic activity, distinguishing from mimics including dermatofibroma. In conclusion, p53 immunohistochemistry is a sensitive adjunctive marker in AFX and PDS. While it is not a substitute for comprehensive histopathological analysis, its routine use enhances diagnostic confidence, assists in assessment of margins and highlights residual tumour in re-excision specimens.