Stage-specific embryonic antigen-4 (SSEA-4) is a ganglioside consist of a glycosphingolipid with a terminal sialic acid residue (N-acetylneuraminic acid).
SSEA-4 was originally discovered to be expressed in early embryonic development as well as in pluripotent stem cells. Expression of SSEA-4 is typically not required for stem-cell pluripotency and is depleted during differentiation. However, SSEA-4 is found to increase rapidly upon tumor formation. Recent studies indicated that SSEA-4 is expressed in many cancer types, including brain cancer, renal cancer, basaloid lung cancer, ovarian cancer, breast cancer, and oral cancer. In particular, the expression of SSEA-4 is associated with poor diagnosis in basaloid lung cancer patients and chemotherapy-resistant cancer cells. On the contrary, expression of SSEA-4 in normal tissues is limited.
In addition, SSEA-4 is thought to be a potential cancer stem cell (CSC) marker in oral cancer, ovarian cancer, and breast cancer.