C4A and cancer: The cause of AE was identified in 59 (37%) cases: 3 (2%) patients had a low plasma C1-INH and C4 levels; 20 (12%) were ACE inhibitor-induced;12 (7%) were associated with autoimmune disorders; 7 (4%) were associated with malignancy; and 17 (11%) were related to use of NSAIDs.