Tn antigen is the immediate precursor of the carcinoma (CA)-associated T antigen; both are masked in non-CA tissues. Tn antigen was detected by absorption of human anti-Tn antibody in 46 of 50 primary breast CAs and in all 6 metastases originating from Tn-positive primary CAs. Thirteen of 25 (52%) anaplastic CAs, but only 2 of 15 (13%) well differentiated CAs had more Tn than T; 1 anaplastic CA had neither antigen. Eighteen of 20 benign breast lesions had no Tn; the 2 positive lesions were premalignant. All 19 breast CAs, studied immunohistochemically, reacted strongly with human polyclonal anti-Tn; benign or normal glandular tissues had minimal or no reactivity. Among live cancer cell lines, the most malignant sublines had more Tn than T on their cell surfaces. Preliminary studies with rodent monoclonal anti-Tn and anti-T antibodies gave immunohistochemical reactivity patterns similar to those of the polyclonal antibodies, but the former were less sensitive in absorption tests. Tn is a CA marker that promises to be useful in tumor detection. Cancer 55561-569, 1985. H E Tn and T blood group precursor antigens are T present, but are masked in most human They are usually covered by covalently linked carbohyd r a t e ~. ~-~
Sometimes, however, spatial arrangement' or high negative charge density due to sialic acid (NAN)E may suffice to render Tn and T antigenic determinants inaccessible to recognition by the immune system, from which they may also be physically oc~luded.~ Because these antigens are ordinarily inaccessible to the immune system, all persons have anti-Tn2 and anti-T antibodies' evoked predominantly by their intestinal flora.loSl1 Both Tn and T antigens are immediate precursors ofthe blood From the