The objective of this study is the evaluation of serum levels of lipid-bound sialic acid (LSA) as a of marker cancer. This is a case-control study, and the levels of LSA were determined with blinded duplicates of cases and controls. Histologic verification of all cancer cases was used to confirm the diagnosis. The study included 135 patients with cancer (breast carcinoma, head and neck squamous cell carcinoma, lung cancer and gastrointestinal cancer) and 95 controls (57 normal subjects and 38 with chronic non-malignant diseases). Marker determination was done by the spectrophotometric procedure of Katopodis with resorcinol. The mean LSA level in the 57 healthy individuals was 15.09 mg/dl (95% C.I., 13.51-16.67), in the entire control group of 95 non-tumoral individuals it was 19.21 mg/dl (17.18-21.24), and in the 135 cancer patients it was 26.64 mg/dl (24.42-28.87). There was a statistically significant difference between patients with chronic non-tumoral diseases and healthy individuals (p<0.001) and also between cancer patients and healthy individuals (p<0.001), but not between cancer patients and patients with chronic non-tumoral diseases (p>0.05). The mean LSA serum values related to tumor site were (mg/dl): breast cancer, 21.49; gastrointestinal tumors, 28.45; head and neck cancer, 28.61 and lung cancer, 32.54. The means according to clinical stage were: complete remission, 18.50, significantly higher than the healthy controls (p<0.05); local disease, 23.50 (p<0.01); locoregional disease, (p<0.05); local disease, 23.50 (p < 0.01); locoregional disease, 27.21 (p < 0.001); metastatic disease, 34.49 (p < 0.001), and relapses, 20.87 (p<0.05). When comparing patients with clinically active cancer with healthy persons, the estimated cutoff value was 19.1 mg/dl, with a sensitivity of 74.7% and a specificity of 74.7%. We conclude that LSA values increase in cases of clinically active cancer and decrease in complete remission. LSA is of great value as a tumor marker in the diagnosis of disease extent.
