CA 15-3

Last revised by Dr Daniel J Bell on 05 Jan 2022

CA 15-3 is a tumor marker used in monitoring breast cancer. The test detects levels of MUC-1, a mucin protein in the blood. MUC-1 is thought to be important in the invasiveness and metastasization of cancer cells.

Mucin-1 is a normal epithelial cellular glycoprotein localized to the apical membrane. In the transformed cell MUC-1 is present on both the complete membrane, and cytoplasmically. Abnormal genetic expression also results in changes to the sugar side chains such that various protein antigens are uncovered, increasing the likelihood of antibodies cross-linking MUC-1. The upthrust of these changes is a greater concentration of MUC-1, which is more antigenic, enabling its use as a tumor marker.

To monitor response of metastatic breast cancer to treatment and recurrence of disease.

CA 15-3 was discovered in 1985 by a Japanese group, and was originally called cancer antigen 15-3 2.

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