a biochemical procedure for diagnosis of three important properties of cells in a biopsy or blood sample : tumor type i . e ., the tissue type that has become neoplastic ; tissue of origin if the tumor has arisen from a metastasis ; and degree of malignancy . the procedure can also be used to obtain antibodies which can be used to determine tissue of origin by immunostaining and to detect tumor antigens appearing in blood by radioimmunoassay . the procedure consists of isolating and analyzing components of a specific subcellular fraction referred to here as the &# 34 ; nuclear matrix &# 34 ;. the nuclear matrix consists of proteins specific to different cell types and nuclear matrix associated dna . the electrophoretic pattern of the proteins and restriction endonuclease digested dna is unique and reproducible within a particular cell type and is therefore useful in diagnosing cell type . changes in these patterns following transformation to a malignant phenotype provide additional diagnostic information .