An elevated level of the free deaminated
sialic acid,
2-keto-3-deoxy-D-glycero-D-galacto-nononic acid (KDN), was first discovered in human
ovarian cancers (OCs), suggesting that KDN may be an oncodevelopmental
antigen (Inoue S, Lin SL, Chang T, Wu SH, Yao CW, Chu TY, Troy FA II, Inoue Y. 1998. J Biol Chem. 273(42):27199-27204). To determine if this unexpected finding was unique to OC, we developed an LC-MS/MS glycomic approach to quantitatively determine the level of free and conjugated forms of KDN, Neu5Ac and Neu5Gc in head and
neck cancers of the throat, and in a subpopulation of matched lymph nodes. These findings were correlated with
tumor (T), nodal (N), metastatic (M) involvement and the differentiation status of the
tumors. The following new findings are reported: (i) The level of free KDN in 49 throat
cancers and a subpopulation of 10 regional lymph nodes accounted for 94.5 and 93.3%, respectively, of the total level of KDN (∼2 µg/g); (ii) in marked contrast, the level of free Neu5Ac in throat
cancer and lymph nodes accounted for only 6.5 and 5.1% of the total level of Neu5Ac (85 µg/g); (3) The level of Neu5Gc (0.03 µg/g) in throat
cancers was 0.30% of the level of Neu5Ac, two-thirds were conjugated and one-third was free. The central importance of these new findings is that the elevated level of free KDN relative to free Neu5Ac and Neu5GC in throat
cancers showing no
lymphatic metastasis, and which are poorly to moderately differentiated, suggests that free KDN may be useful as a
biomarker for detecting some early-stage
cancers at biopsy, and be of possible prognostic value in determining the potential degree of
malignancy.