Although previously relatively high tissue transglutaminase expression levels in MDA-MB-231 tumour cell lysates were observed [10], and both TG2 expression and activity were further confirmed in xenografted MDA-MB-231 tumour tissue by means of immunohistochemistry and in vitro autoradiography [19, 20], it is unknown to what extent TG2 shows transamidation activity in a biological setting such as the present MDA-MB-231 tumour model. Here, TGM2 is linked to neoplasm.