Elevation of serum riboflavin carrier protein in breast cancer.

Presently available tumor markers have had a limited clinical impact. Riboflavin carrier protein (RCP) is an estrogen inducible protein that occupies a key position in riboflavin metabolism. Because other vitamin carrier proteins (VCP) have been shown to be overexpressed in patients with malignant disease, we evaluated serum RCP levels in patients with adenocarcinoma of the breast. In this prospective blinded study, patients with breast cancer, benign breast disease, and healthy controls were analyzed for RCP levels. Using a highly sensitive RIA, we observed that serum RCP levels were significantly elevated in women with breast cancer (n = 52) as compared with control subjects [n = 50; 6.06 +/- 7.27 ng/ml versus 0.70 +/- 0.19 ng/ml (mean +/- SD), respectively; P < 0.0001]. A serum RCP level of > or = 1.0 ng/ml was highly predictive of the presence of breast cancer, detecting 88% of tumors in stages I-II and 100% of tumors in stages III-IV. Overall, this RCP assay has a sensitivity of 92.3%, a specificity of 88%, a positive predictive value of 88.9%, and a negative predictive value of 91.7%. These results show increased serum levels of RCP in breast adenocarcinoma patients and suggest that RCP levels may be useful as a new marker for breast cancer. The positive predictive value in early-stage breast cancer suggests that the RCP assay may be a useful adjunct to present screening technology.