Publisher Summary DS6 is a newly developed antibody that uses human serous ovarian carcinoma as the immunogen. In immunohistochemical studies, the DS6 antibody detects a tumor-associated glycoprotein antigen in human tissues that has been provisionally named CA6. The DS6 antibody shows immunohistochemical reactivity in both acetone-permeablized frozen sections and in formalin-fixed, paraffin-embedded (FFPE) human tissue sections. The immunohistochemical reactivity of DS6 with normal adult human tissues and human neoplasms has been discussed in the chapter. Studies have shown that CA6 has a limited distribution in normal human tissues. The relationship of CA6 expression to tumor grade or prognosis has not been systematically evaluated in breast carcinomas, so the significance of CA6 expression in breast carcinomas is uncertain.