Background: KL-6 is a mucin that is increased in interstitial lung diseases (ILD), and in some malignancies. CA 15-3, a tumor marker for breast cancer, refers to the same mucin but utilizes antibodies against different epitopes.
Objective: The aim of our study was to evaluate CA 15-3 as a viable alternative to KL-6 as a for ILDs with and without fibrosis.
Design: Serum from 242 patients with ILDs and from 327 healthy controls were included and KL-6 and CA 15-3 were measured in all subjects. Regression analyses and ROC curves were used to compare the performances of both markers.
Results: KL-6 and CA 15-3 levels were both significantly higher in the ILD patients compared to the controls (p < 0.0001). A weak yet significant correlation was found between serum KL-6 and CA 15-3 levels in the controls (R = 0.39, p < 0.0001), but showed a much higher correlation in the patient group (R = 0.85, p < 0.0001). CA 15-3 correlated best with KL-6 in patients with fibrotic ILDs (R = 0.83, p < 0.0001). KL-6 performed better as a marker compared to CA 15-3 in most ILDs. Both markers performed best in identifying idiopathic pulmonary fibrosis (IPF) and were equally able to differentiate between ILDs with and without fibrosis: (sensitivity and specificity %): 100/97, 95/92, and 90/72, respectively.
Conclusion: CA 15-3 and KL-6 are equally sensitive and specific in terms of differentiating between ILDs with and without fibrosis. The wide availability, ease of use, and cost effectiveness, make CA 15-3 a viable alternative for KL-6 as a possible marker for pulmonary fibrosis.