Recurrence of a cancer is a serious event, in particular the appearance of distant metastases, which can no longer be resected. The cure rate of patients in this situation is generally very poor. Patients with a high risk of recurrent disease are therefore given adjuvant treatment already after radical surgery, although the existence of remaining tumour cells cannot be diagnosed at this stage. Thus, there is a great need for a method to diagnose these patients, in order to be able to give them an adequate treatment from the very beginning of the post-surgical period.
Several factors of prognostic significance for colorectal cancer (CRC) have been identified. Dukes' classification or staging based on the TNM classification gives good prognostic information, but still there is a great need for tests giving more detailed prognostic information especially for patients with Dukes' B and C or stage II and III cancers. Therefore the prognostic value of several molecular and genetic factors has been investigated. So far no single parameter, which allows individual monitoring of CRC patients, has been described. Cancer is often associated with a systemic chronic inflammation resulting in production of cytokines e.g. interleukin-6 (IL-6) and TNF-α and induction of acute phase reactants, such as C-reactive protein (CRP). High serum levels of CRP has been reported to correlate to poor prognosis, but still a fairly high recurrence rate is found in patients with normal serum levels of CRP, thus reducing the value of this parameter for individual monitoring of cancer patients. Therefore, scores based on several parameters, e.g. serum level of CRP and TNM-stage has been proposed. The importance of the immune system for the control and/or prognosis of CRC is suggested by the correlation between infiltration of lymphocytes and good prognosis/prolonged survival.
Cancer related immunosuppression is often associated with a systemic, chronic inflammation with increased pathological production of several cytokines, wherein cytokines are chemical mediators released by cells that affect the behaviour of other cells, (eg. IL-1βS, IL-1Ra IL-6, IL-10, IL-17, TNF-α, PGE2, TGF-β). IL-6, and TNF-α are involved in a paraneoplastic syndrome frequently found in cancer patients. This syndrome is characterized by a poor performance status, low-grade fever, anorexia, weight-loss, fatigue and distortion of various biochemical laboratory parameters. This condition is said to correlate to the tumour burden of the patient, being worse in more advanced disease. In particular, IL-6, a pleiotropic, proinflammatory cytokine, is of importance for the regulation of immune reactivity (Lotz: 1995. Cancer Treat Res 80:209; Barton B E. 1996. Med Res Rev 16:87). In addition to its regulatory role in immune and inflammatory responses, it regulates hepatic acute-phase protein synthesis, hematopoiesis and bone metabolism. IL-6 production can be induced by a large variety of stimuli which includes;                Other cytokines (such as IL-1β, IL-17 and TNF-α)        Microbial products (such as endotoxins, e.g. lipopolysaccharide from Gram-negative bacteria like Escherichia coli, formalin fixed or dried Staphylococcus aureus, mycobacterial cell wall components or synthetic constructs thereof (muramyl dipeptide) and Staphylococcus aureus anterotixins A (SEA) and B (SEB)        Mitogens, such as Phytohemagglutinin (PHA) and Concanavalin A (ConA)        Plasma/serum factors, such as IgG, IgA, immunocomplexes and fibrinogen or fibrin degradation products, e.g. D-dimer        Complement factors, such as C3a and C5a        Acute-phase reactants, such as C-reactive protein (CRP)        Extracellular matrix (ECM) components, such as fibronectin, vitronectin or proteolytic fragments or synthetic peptides thereof        Neuropeptides        
In addition, other pro-inflammatory cytokines (TNF-α, IL-1 and IL-8) can be induced in mononuclear cells by P-selectin (from platelets), free hemoglobin and soluble CD23. An increased serum concentration of IL-6 is often found in cancer patients, especially in patients with advanced disease and has been reported to correlate with a poor prognosis in various types of cancer, e.g. multiple myeloma, chronic lymphocytic leukemia, renal cell carcinoma, prostate cancer, ovarian cancer, metastatic breast cancer, pancreatic carcinoma and colorectal cancer. IL-6 may also be involved in the malignant process as an autocrine or paracrine growth factor in cancers like renal cell carcinoma, multiple myeloma, prostate cancer, colon cancer and Kaposi's sarcoma. Except for a possible prognostic value, the information provided by determination of serum concentrations of factors such as IL-6 can, can be questioned. The cellular origin of these serum factors is often unknown, they are immensely diluted in serum and their half-life is not accounted for. The information obtained from serum determinations of such factors is therefore most likely just a faint reflection of the mechanisms behind their appearance in serum.
An increased systemic concentration of IL-6 has been reported to correlate with a poor response to chemotherapy and it is well documented that patients with increased IL-6 and/or CRP serum levels cannot be successfully treated with immunotherapy.
The source of serum IL-6 in cancer patients is still somewhat unclear. Although IL-6 can be produced by a broad range of normal cells such as fibroblasts, monocytes, T lymphocytes, endothelial cells and keratinocytes it is generally assumed to be derived from the tumour as it may be produced by certain malignant cells. In a study of 12 colon cancer patients, IL-6 mRNA was expressed in tumour tissue in 83% of the cases but only in one patient in normal mucosa (Piancatelli et al. 1999. J Immunother 22:25) and in another study by Kinoshita et al. it was shown that the IL-6 concentration in tumour tissue of colorectal carcinoma patients were significantly higher than in normal mucosa and was correlated with the serum IL-6 concentration. In addition, serum level of IL-6 was correlated with such parameters as tumour size and proliferative activity of the tumour (Kinoshita et al. 1999 Cancer 85:2526)
Based on these observations IL-6 was chosen as an interesting parameter of dysregulation of the immune system in cancer patients. In the present study LPS-induced IL-6 production by blood cells from CRC patients was determined preoperatively and a possible correlation to the prognosis of these patients was analysed.