nm23 protein expression and p53 immunoreactivity in cutaneous fibrohistiocytic tumors

Recent data indicate that reduced expression of the 17-kD protein encoded by the nm23 gene may be important in the pathogenesis of several types of human tumors. Immunohistochemistry was performed using a murine monoclonal antibody, NCL-nm23 (Novocastra, 1:150 dilution) to investigate nm23 protein immunoreactivity in a group of locally aggressive cutaneous fibrohistiocytic tumors; dermatofibrosarcoma protuberans (DFSP) (n = 14) and atypical fibroxanthoma (AFX) (n = 7). Cases of dermatofibroma (DF) (n = 17) formed the benign control group. Comparison with p53 protein immunoreactivity in the same cases studied previously was made. Strong immunohistological expression of the nm23 protein was seen in most of the cases of DF (n = 15; 88%) in the form of strong cytoplasmic immunolabelling without nuclear staining. However, strong nm23 immunoreactivity was observed in only a minority of the cases of DFSP (n = 5; 36%) and AFX (n = 2; 29%). Statistically significant differences in nm23 immunoreactivity were found between DFSP and DF (p = 0.008, chi 2 test with continuity correction) and between AFX and DF (p = 0.015; chi 2 test with continuity correction). No significant difference was seen between DFSP and AFX (p = 0.87, chi 2 test with continuity correction). There was inverse correlation between nm23 and p53 immunoreactivity (r = 0.331; r2 = 0.109; p = 0.046; simple regression analysis). In summary, nm23 protein immunoreactivity is reduced in DFSP and AFX but not in dermatofibroma suggesting that reduced expression of the protein may be important in influencing the behavior of fibrohistiocytic tumors, although this is not well characterised. nm23 protein expression is also found to be inversely related to p53 immunohistological expression in these tumors.