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 immunohistochemical staining in whole tissue sections, evaluated the tissue microarray technique, and assessed immunohistochemical heterogeneity using the proliferation marker Ki-67 in 47 histopathologic tumor blocks from 11 MFHs. Whole tissue sections were assessed counting 400 cells along a line and counting all cells in 10 high-power fields (0.16 mm2) with mean Ki-67 expression levels of 13% and 11%, respectively. For the tissue microarray technique, two to three 0.6-mm diameter biopsies were studied from each of the 47 tumor blocks. Good correlation was obtained between whole tissue immunohistochemistry and tissue microarray with the microarray method, giving on average 8.6% greater Ki-67 expression levels than the reference method. Immunohistochemical tumor heterogeneity, evaluated using the high-power field method, 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 levels for Ki-67 comparable with whole tissue methods in MFH, but because of tumor heterogeneity, several tumor blocks ideally should be studied and, because of loss of material in the microarray process, multiple biopsies should be taken. The feasibility of tissue microarray for immunohistochemical studies of soft tissue sarcomas offers new possibilities to study multiple markers in large tumor materials.