CCL21 and small cell lung carcinoma: These results suggest that the serum proteins CCL14, CCL27, and CXCL13 are risk factors for non-small cell lung cancer, while CCL19 is a protective factor for non-small cell lung cancer, CXCL9 is a risk factor for small cell lung cancer, while CCL20 and CCL21 are protective factors for small cell lung cancer.