Heparin, dextran 1000 and metastasis formation after I.V. tumour cell injection in dextran non-sensitive rats

A meta-analysis and systematic review of the efficacy and safety of anticoagulants as cancer treatment: impact on survival and bleeding complications

BACKGROUND

Preclinical evidence suggests that anticoagulants, in particular the low-molecular-weight heparins (LMWH), exert an antitumor effect, whereas clinical trials have reported conflicting results. The authors conducted a comprehensive, systematic review and meta-analysis of the evidence from randomized controlled trials (RCTs), to evaluate the impact of anticoagulants on survival and safety in cancer patients without venous thromboembolism.

METHODS

A comprehensive systematic literature review of RCTs was performed without language restrictions through May 2006 with subsequent updates to the end of 2006, including an exhaustive search of electronic databases, major conference proceedings, article references, and content experts. Two reviewers extracted data independently. Primary study outcomes were 1-year overall mortality and all bleeding complications. Major and fatal bleeding complications were secondary outcomes.

RESULTS

Across all 11 studies that were identified, anticoagulation significantly decreased 1-year overall mortality with a relative risk (RR) of 0.905 (95% confidence interval [95% CI], 0.847-0.967; P = .003). The RR for mortality was 0.877 (95% CI, 0.789-0.975; P = .015) for LMWH, compared with an RR of 0.942 (95% CI, 0.854-1.040; P = .239) for warfarin, resulting in an absolute risk difference (ARD) of 8% for LMWH and an ARD of 3% for warfarin. Improved survival with anticoagulation may be dependent on tumor type. Major bleeding episodes occurred less frequently in patients who received LMWH (ARD, 1%) compared with patients who received warfarin (ARD, 11.5%; P < .0001). Overall, fatal bleeding occurred rarely (ARD, 0.32%; P = .542).

CONCLUSIONS

Anticoagulants, particularly LMWH, significantly improved overall survival in cancer patients without venous thrombosis while increasing the risk for bleeding complications. However, given the limitations of available data, the use of anticoagulants as antineoplastic therapy cannot be recommended until additional RCTs confirm these results.

Basic mechanisms of metastasis

Metastatic disease is responsible for the majority of deaths caused by cancer. The process of metastasis is an orderly, stepwise process that results in the selection of cells that possess the capability to establish viable metastases. These cells must be locally invasive and be able to survive the physical traumas of dissemination and normal host defenses. Once metastatic cells have been arrested in a capillary bed, they must be able to invade the host organ parenchyma and survive in that milieu. Studies in a number of model systems have documented the phenotypic alterations in cells that have "metastatic potential." These differences may stem from normal tumor cell heterogeneity and surprisingly reflect only minor differences in gene expression. The role of activated oncogenes in metastasis is unclear, but a number of laboratories have documented that transfection with activated Ha-Ras results in increased metastatic potential. An increased understanding of the genetic basis of metastatic potential may suggest new directions for intervening in this deadly process.

The correlation of pretreatment transurethral resection of prostatic cancer with tumor dissemination and disease-free survival. A univariate and multivariate analysis

A multivariate Cox's hazard function analysis was performed on the prognostic variables selected from 240 patients with localized carcinoma of the prostate who received external beam radiotherapy to analyze the association between the method of biopsy and disease-free survival. The patients received 4500 cGy to the pelvis followed by a 2-week treatment rest and then an additional 2000 cGy to the reduced prostatic volume. Median follow-up was 4 years (range, 1-9 years). The 5-year actuarial local control rate was 91%. There was no difference in local control relative to the method of biopsy (needle biopsy or transurethral resection of the prostate [TURP]). The 5-year actuarial risks of metastases were 28% and 48% for the needle biopsy and TURP groups, respectively (P less than 0.01). The 5-year disease-free survival for the needle biopsy and TURP groups were 55% and 42%, respectively (P less than 0.05). This difference maintained statistical significance for Stage C and Grade III tumors. A multivariate analysis demonstrated that "method of biopsy" was the third most powerful variable after serum acid phosphatase level and modified Broders' grade in predicting disease-free survival. Patients who had TURP had an almost twofold higher relative risk of disease progression than those who had needle biopsy. This study established the correlation of the method of biopsy with a lower probability of disease-free survival over and above the information obtained from the clinical stage, histologic grade, presence or absence of symptoms of obstruction, acid phosphatase level, and lymph node status. The association of TURP with tumor dissemination is discussed with reference to the mechanism of metastasis formation and prevention.

Metastasis in the androgen-insensitive Nb rat prostatic carcinoma system

This unit has in the past evaluated the Nb rat prostatic adenocarcinoma model with respect to chemotherapies. Recently, this unit has been evaluating agents that may have a role in decreasing metastatic rate. The three androgen-insensitive tumors, Nb Pr A.I. I, II, III, have been evaluated herein. Agents that have been used include indomethacin, heparin, heparin plus cortisone, and heparan sulfate (SP54). It has been shown that these agents do play a role in reducing the metastasis. In evaluation of Nb Pr A.I, I, control animals had a metastatic rate of 57%. In treatment with indocin, only 21% of the animals, three of 14 animals treated, had a metastasis, and treatment with heparin and cortisone resulted in one of 14 animals having metastasis. Similar observations were seen when treatment with SP54 and heparin was evaluated in the Nb Pr A.I. III; 18 and 27% of treatment group animals had metastasis, whereas 55% of control groups had metastasis. Similarly, in the Nb Pr A.I. II evaluation, control animals having a metastatic rate of 43% had heparin plus cortisone and heparin alone, and this particular tumor model revealed complete resolution with no animals having metastatic disease. The majority of these agents have not effected tumor volume in terms of reduction as much as the best chemotherapeutic agents in this model system include cyclophosphamide and cis-platinum.

Control of metastases in the Nb rat prostatic adenocarcinoma model

Chemotherapeutic agents, as well as acetyl-salicylic acid, heparin, and indocin, were evaluated in regard to their effect on the rate of metastasis in the androgen-insensitive Noble rat prostate adenocarcinoma system. Acetyl salicylic acid, heparin and indocin were similar to the chemotherapeutic agents cyclophosphamide and adriamycin in reducing the incidence of metastases, but had less effect on tumor volume. In the heparin and indocin groups, the rate of metastases was approximately one half that of the control group (25% vs. 59%). In all three experiments evaluating heparin and indocin, there was a decrease in the number of animals with metastasis compared with control groups.

Studies on mechanisms involved in metastasis formation from circulating tumor cells. Factors influencing tumor cell lodgement during normal and post-traumatic conditions

As shown in earlier studies the formation of metastases after i.v. tumor cell injection in rats is increased in the immediate post-traumatic period and treatment with heparin, thrombocytopenia, and defibrinogenation decreases the formation of metastases. Thrombocytopenia also inhibits the stimulating effect of trauma on metastasis formation. The results of the studies reported in this paper show that the changes of metastasis formation induced by the factors mentioned above with few exceptions are well correlated to the lodgement of the injected tumor cells. Thus, heparin treatment and thrombocytopenia decrease the pulmonary lodgement of i.v. injected tumor cells. Trauma increases the pulmonary lodgement of i.v. injected tumor cells but when trauma is combined with thrombocytopenia, the effect of thrombocytopenia dominates and the pulmonary lodgement of tumor cells decreases when compared to control conditions. Despite this, trauma still gives rise to increased tumor cell lodgement during thrombocytopenia.

Initial tumor cell arrest in animals of defined coagulative status

Experiments were made to evaluate the potential role played by thrombogenic factors on the hematogenous arrest of circulating tumor cells in mice with demonstrable coagulopathies associated with the presence of a primary tumor, by administration of "therapeutic" doses of anticoagulants. The effects of warfarin, aspirin and heparin administration on the early arrest patterns of 125IdUrd-labelled TA3 carcinoma and Gardner lymphosarcoma cells injected intravenously into tumor-bearing mice were examined. Several hematologic parameters of carcinoma- and lymphosarcoma-bearing animals were measured prior to anticoagulation experiments and the results indicated that mice had coagulopathies similar to those found in cancer patients with disseminated intravascular coagulation syndrome, i.e., thrombocytopenia and elevated fibrinogen levels. Despite the presence of coagulation abnormalities and effective anticoagulation in recipient animals, all three agents were without effect on localization patterns of both tumor types. It was concluded that the proposed involvement of thrombogenesis in metastasis was probably not due to any role played by those clotting factors inhibited by aspirin, warfarin and heparin in early intravascular tumor cell arrest.

Pulmonary metastasis formation after intravenous tumour cell injection in defibrinogenated rats

In this study a state of temporary defibrinogenation was induced in rats by Defibrase treatment. It was found that the formation of pulmonary metastases after intravenous tumour cell injection was decreased in defibrinogenated rats. However, defibrinogenation did not influence the effect of trauma and infusion of dextran 1000 on metastasis formation. Both these procedures stimulated the formation of metastases in defibrinogenated rats. These results indicate, that fibrinogen and/or fibrin are of importance for the formation of metastases but that the stimulating effect of trauma and dextran 1000 on metastasis formation is independent of fibrinogen and/or fibrin.