C4A and lung carcinoma: CYFRA 21-1 has long been proposed as a lung cancer biomarker in bronchial fluids [7, 14], plasma proteins are increased in BAL fluids from lung cancer patients [15], C4 is an abundant plasma protein from which C4d is generated after complement activation [16], and C5a is an active complement fragment increased in plasma samples from patients with non-small cell lung cancer [17].