Tissue microarray technique in soft tissue sarcoma: Immunohistochemical Ki-67 expression in malignant fibrous histiocytoma

Malignant fibrous histiocytoma (MFH) represents a heterogeneous soft tissue sarcoma entity. The authors compared different methods to determine immuno histochemical staining in whole tissue sections, evaluated the tissue micro array technique, and assessed immunohistochemical heterogeneity using the p roliferation marker Ki-67 in 47 histopathologic tumor blocks from 11 MFHs. Whole tissue sections were assessed counting 400 cells along a line and cou nting all cells in 10 high-power fields (0.16 mm(2)) with mean Ki-67 expres sion levels of 13% and 11%, respectively. For the tissue microarray techniq ue, two to three 0.6-mm diameter biopsies were studied from each of the 47 tumor blocks. Good correlation was obtained between whole tissue immunohist ochemistry and tissue microarray with the microarray method, giving on aver age 8.6% greater Ki-67 expression levels than the reference method. Immunoh istochemical tumor heterogeneity, evaluated using the high-power field meth od, showed a median standard deviation of 2.3% within the tumor blocks and 2.5% between the blocks from the same tumor. The authors concluded that the tissue microarray technique yields good quality staining and expression le vels for Ki-67 comparable with whole tissue methods in MFH, but because of tumor heterogeneity, several tumor blocks ideally should be studied and, be cause of loss of material in the microarray process, multiple biopsies shou ld be taken. The feasibility of tissue microarray for immunohistochemical s tudies of soft tissue sarcomas offers new possibilities to study multiple m arkers in large tumor materials.