Evaluation of serum KL-6, a mucin-like glycoprotein, as a tumor marker for breast cancer.

The utility of serum KL-6 as a tumor marker for breast cancer was evaluated in this study. The sera from 146 patients with breast cancer, 13 with benign breast disease, and 108 healthy individuals were measured for KL-6 titer using a sandwich enzyme immunoassay method. Carcinoembryonic antigen (CEA) and carbohydrate antigen 15-3 (CA15-3) titers were also tested in the same sera from the patients. The mean KL-6 titer of patients with primary breast cancer was 673 units/ml, which was significantly higher than that of benign and healthy individuals (P = 0.037 and P < 0.0001, respectively). The titer of patients with relapsed breast cancer was 1964 units/ml, which was also higher than that of primary cancer (P = 0.013). KL-6 titer was related to tumor stage, distant metastasis, and relapse site (P = 0.0053, P < 0.0001, and P = 0.0251, respectively). Using the cutoff value of 467 units/ml, the sensitivity of KL-6 was 31% for primary breast cancer (16% for stage I and 29% for stage II) and 73% for relapsed breast cancer (50% for local relapse and 89% for distant relapse). The specificity was 92%. The sensitivity of KL-6 was higher than that of CA15-3 and CEA. Combination of the three markers, followed by KL-6 and CEA, raised the sensitivity for primary breast cancer. Single use of KL-6 demonstrated a higher sensitivity than in each combination for relapsed breast cancer. In conclusion, serum KL-6 may be helpful for clinical use as a tumor marker for breast cancer, and it may play an important role, especially in the surveillance of disease relapse.