Atypical fibroxanthoma versus benign and malignant fibrous histiocytoma. A comparative study of their proliferative activity using MIB-1, DNA flow cytometry, and p53 immunostaining.

BACKGROUND: MIB-1 was found to be detectable in formalin fixed, paraffin embedded materials with microwave treatment using Ki-67 monoclonal antibody, and immunostaining has been widely documented as a useful marker of proliferation. Because atypical fibroxanthoma (AFX) is regarded as a fibrohistiocytic tumor with an intermediate potential, the proliferative activity of AFX was compared with that of benign and malignant fibrous histiocytomas.
METHODS: Thirty-eight soft tissue tumors including atypical fibroxanthoma (n = 5), benign fibrous histiocytoma (FH) (n = 17) and malignant fibrous histiocytoma (MFH) (n = 16) were examined using immunohistochemistry to determine MIB-1, DNA flow cytometry, and p53 (PAb 1801) immunostaining.
RESULTS: The mean of the MIB-1 labeling index (MIB-1 LI), defined as the percentage of positive cells for more than 500 cells, was determined in an increasing order as follows: FH, 3.3 +/- 1.8; AFX, 12.2 +/- 6.3; and MFH, 21.5 +/- 10.2. However, the MIB-1 LI of each case in AFX was considerably scattered, and the MIB-1 LI of AFX and MFH overlapped each other. A DNA analysis revealed that the proliferative index (S+G2+M fraction) showed no significant correlation with the MIB-1 LI, and an aneuploid pattern was present in only five (42%) of 12 cases of MFH. p53 positivity was detected in 2 (40%) of 5 cases of AFX and 6 (38%) of 16 cases of MFH.
CONCLUSIONS: Although AFX shows a lower degree in the MIB-1 LI than MFH, the MIB-1 LI shows a limited value in relation to the biologic activity of fibrohistiocytic tumors. Aneuploidy demonstrates a malignant potential in fibrohistiocytic tumors.