BackgroundLectin pathway proteases activate coagulation and may theoretically play a role in the increased thrombosis risk in cancer, which is especially high during surgery. AimsTo investigate lectin pathway proteins during lung cancer surgery, the influence of low molecular weight heparin (LMWH) on lectin pathway proteins, and correlations between lectin pathway proteins and coagulation. MethodsFifty lung cancer patients undergoing video-assisted thoracoscopic surgery lobectomy were randomised to LMWH, n = 26, or no anticoagulant (control), n = 24. Pre-, intra- and postoperative lectin pathway protein concentrations (mannose-binding lectin (MBL), H– and M-ficolin, collectin liver-1, MBL-associated serine protease (MASP)-1, -2 and -3, MBL-associated proteins MAp44 and MAp19) were assessed using a time-resolved immunofluorometric assay, and fibrinogen, fibrin d-dimer, and thrombin generation were analysed. ResultsFor all proteins except MASP-1, concentrations decreased during surgery in both groups; most markedly M-ficolin which decreased 49% (median: 2836 [quartiles:2297–3505] to 1424 [1187–2199] ng/ml) (LMWH group) and 43% (2974 [2539–3510] to 1685 [1391–2076] ng/ml) (control group), while MBL decreased 12% (1936 [823–2801] to 1702 [676–2830] ng/ml) (LMWH) and 23% (1526 [250–2412] to 1175 [229–1947]) (controls). No differences in postoperative change were observed between groups except for MAp19 (p = 0.03) which decreased 9% (401 [337–467] to 364 [288–416] ng/ml) (LMWH) vs 28% (370 [272–468] to 268 [212–379] ng/ml) (controls). No correlation was found between lectin pathway proteins and coagulation (r = −0.23–0.28, p > 0.06) except for M-ficolin and fibrinogen (r = 0.29–0.36, p = 0.01–0.04). ConclusionLectin pathway proteins were influenced by surgery but not by LMWH. No consistent correlation was found between lectin pathway proteins and coagulation.