P16 IMMUNOHISTOCHEMISTRY AS A MARKER TO DISTINGUISH BETWEEN ATYPICAL LIPOMATOUS TUMOUR/WELL-DIFFERENTIATED LIPOSARCOMA AND BENIGN ADIPOCYTIC LESIONS

Abstract

Introduction Atypical lipomatous tumour (ALT)/well-differentiated liposarcoma (WDL) is the most common subtype of liposarcoma. There are marked similarities between normal fat, lipomas and ALT/WDL, making the histological diagnosis of ALT/WDL challenging. In this study we compared the expression of p16 in specimens of ALT/WDL to its expression in other adipocytic tumours and normal adipose tissue to determine whether it is a useful ancilliary tool to distinguish between benign and malignant adipocytic tumours. Methods Thirty liposarcomas, including four with areas of dedifferentiation, 30 lipomas, 26 unusual adipocytic tumours and 16 specimens of normal adipose tissue were included in the study. Immunohistochemistry for p16 was performed on all the specimens. p16 expression was reported as 1+ positive, 2+ positive, 3+ positive and negative. Results Twenty of the 30 specimens of ALT/WDL were 3+ positive, four were 2+ positive and one was 1+ positive. Five specimens were negative, of which four were needle biopsies. All the lipomas and normal adipose tissue were negative. None of the unusual adipocytic lesions were 3+ positive. p16 positivity was significantly more common in ALT/WDL than in the other three groups (p < 0.0001). Conclusions Our findings support the use of p16 immunohistochemistry as a useful marker to distinguish between benign and malignant adipocytic lesions.