The data presented here defines the CIZ1b plasma biomarker as a small CIZ1 fragment spanning the exon 14b/15 junction stably complexed with fibrinogen alpha chain, and has lead to proof of concept validation of a quantitative sandwich ELISA that can detect the CIZ1b/fibrinogen alpha complex in lung cancer patients, via a simple immunoassay of blood. The gene discussed is CIZ1; the disease is lung carcinoma.