Sigma S, a measure of reactive sulfur groups of immunoglobulin G, is a sensitive tumor marker discriminating different stages of breast cancer.

Sigma S is a measure of the disulfide bonds and free thiol groups of serum immunoglobulin (Ig) G, as determined by the reaction with dithionitrobenzoate. Significant decreases of sigma S previously were detected in malignant compared with benign diseases of various organs. This study shows the application of sigma S for the diagnosis of breast cancer. The following results were obtained. First, 132 patients with benign breast diseases showed a sigma S of 1.48 +/- 0.29 (standard deviation) per mole IgG; this was not different from 1.51 +/- 0.36 found in 182 controls. In contrast, IgG from 198 patients with primary breast carcinoma of all four stages (tumor-node-metastasis system) gave a sigma S of 1.22 +/- 0.29, a significant (P less than 0.0001) decrease of sigma S from benign to malignant breast disease. Second, sigma S values of single Stages I, II, III, and IV, were 1.27 (n = 59), 1.23 (n = 83), 1.19 (n = 35), and 1.10 (n = 21), respectively, each significantly different from sigma S in benign disease and showing a decreasing trend with increasing tumor progress. Differences were significant between Stages I and IV (P less than 0.025) and II and IV (P less than 0.05). Third, 63% of Stage I breast carcinoma patients had sigma S values below a critical threshold of 1.38. This serum positivity rose to 90% in Stage IV. These values exceeded those reported with other tumor markers. The overall power of sigma S to distinguish between benign and malignant breast disease had a specificity of 61% and a sensitivity of 78%. Early stages (I and II) of breast cancer could be distinguished from benign diseases with 64% specificity and 69% sensitivity. Advanced Stage IV could be discriminated from early Stages I and II with 55% specificity and 71% sensitivity. Thus, the analysis of sigma S may significantly contribute to the surveillance of patients with breast cancer.