Haemoccult test properties according to type and number of positive slides in mass screening for colorectal cancer

Despite encouraging results from recent studies, there is still no consensus to undertake mass screening using the Haemoccult test in the general population. The success of mass screening for colorectal cancer depends among other things on Haemoccult test properties. In on-going screening programmes, the Haemoccult test consists of six slides and a test is considered positive if at least one slide is coloured. The aim of this work was to study the influence of the type and number of positive slides on the Haemoccult test's positive predictive value and characteristics of screened lesions. This work focuses on 63,958 first tests in a mass screening programme in Calvados (France) among people aged 45-74 years. There was a linear relation between the positive predictive value for cancer or an adenoma larger than 1 cm and the number of positive slides (P < 10(-4)). The positive predictive value for cancer or large adenoma was significantly higher when 4-6 slides were positive (44.3%) than when only 1-3 were positive (19.1%) (P < 10(-4)). In this latter group, the subjects in whom tumours were detected were younger and had significantly less extensive cancers. Borderline tests (no slides positive and at least one slide with a blue coloration confined to the edges) had a positive predictive value for cancer or an adenoma larger than 1 cm no different to that of tests with 1-3 positive slides. Subjects with borderline results were markedly younger than the others and had less extensive cancers and rectal localisation more often than the others. Our results suggest that (1) increasing the number of positive slides required to declare a test positive leads to an increase in the positive predictive value but is not to be recommended because of the sensitivity of the test and (2) considering borderline Haemoccult tests as positive in on-going and future mass screening campaigns would allow an increase in the sensitivity of the test, especially for rectal cancer and low extensive tumours without any decrease in its positive predictive value.

Participants' characteristics in a French colorectal cancer mass screening campaign

BACKGROUND

Participation by the target population is clearly a key element in the success of mass screening programs for colorectal cancer. In France, involvement of general practitioners in test distribution is essential to reach a satisfactory participation rate, but other forms of recruitment also have to be organized. The aim of this study was to determine the influence of demographic characteristics such as sex, age, and place of residence on the participation rate in a French mass screening according to different recruitment methods.

METHODS

The Hemoccult IIR test was proposed in three consecutive ways: spontaneously by general practitioners and occupational doctors during appointments (phase 1), by postal invitation (phase 2), and finally by direct mailing of the test (phase 3). The target population consisted of 11,947 people between 45 and 74 years of age, living in a district of the French county of Calvados, between March 1991 and April 1993.

RESULTS

The overall participation rate was 51.3%. Forty-nine percent of all the tests were done during phase 1, 31% during phase 2, and 20% during phase 3. The overall participation rate varied essentially according to the place of residence, from 65.5% in urban areas and 48.9% in intermediate areas to 27.7% in rural areas. The overall participation rate was also higher for females (57%) than for males (45%) and for those 60 years and older (53.9%) than for those below this age (49.2%). The proportion of tests done during phase 1 was lowest among the youngest and the oldest age groups (37.5% in the 45- to 49-year class and 45.2% in the 70- to 74-year class) and among people living in the rural environment (respectively 55.3%, 45.5%, and 35.9% in urban, intermediate, and rural areas).

CONCLUSIONS

This study shows that place of residence strongly influences the global participation rate in mass screening for colorectal cancer in France, whereas sex and age have little influence. Recruitment methods complementary to distribution by general practitioners must be organized, especially for the youngest and oldest age groups (45-49 years and 70-74 years) and above all for people living in rural areas. The social, cultural, and psychological reasons for these differences remain to be investigated, with the aim of adapting mass screening strategies to the different population groups.

Protein tyrosine kinase activation is required for LPS and PMA induction of tissue factor mRNA in human blood monocytes

Tissue factor (TF) is a transmembrane glycoprotein which assembles with factor VIIa on cell surfaces to form a proteolytically active cofactor-enzyme complex; the TF/VIIa complex initiates the coagulation protease cascade. In response to bacterial lipopolysaccharide (LPS) and phorbol-12 myristate 13-acetate (PMA), monocytes synthesize and express TF on their surface. However, the mechanisms by which LPS and PMA activate TF synthesis by human blood monocytes are not fully understood. As it has been established that LPS and PMA activate protein tyrosine kinase (PTK) in monocytes, we studied the role of PTK in LPS and PMA induction of TF by human blood monocytes. Both LPS- and PMA-induced TF activity was inhibited in a concentration-dependent manner by the protein tyrosine kinase-specific inhibitors herbimycin A and genistein. TF antigen determination confirmed that LPS- and PMA-induced cell surface TF protein levels decreased in parallel to TF functional activity under herbimycin A and genistein treatment. Northern blot analysis of total RNA from LPS- and PMA-stimulated monocytes showed a concentration-dependent decrease in TF mRNA levels in response to herbimycin A and genistein. The rate of decay of LPS-induced TF mRNA, evaluated after the arrest of transcription by actinomycin D was not affected by genistein and herbimycin A, suggesting that the inhibitory effects occur at least partly at the transcriptional level. We conclude that LPS- and PMA-induced TF production by human monocytes is dependent on tyrosine kinase activation.

Interleukin-10 and pentoxifylline inhibit C-reactive protein-induced tissue factor gene expression in peripheral human blood monocytes

Fibrin deposition is an integral feature of the inflammatory response. In response to C-reactive protein (CRP), an acute-phase reactant, blood monocytes synthesize and express tissue factor (TF), the main initiator of blood coagulation. We report the inhibitory effect of interleukin 10 (IL-10) and that of pentoxifylline, a methyl xanthine derivative, on monocyte expression of TF activity, TF protein and TF mRNA in response to CRP. These agents may be of use in diseases where a TF-induced prothrombotic state is detrimental.

Endotoxin-induced tissue factor in human monocytes is dependent upon protein kinase C activation

Tissue factor (TF) is a transmembrane receptor which, in association with factors VII and VIIa, activates factor IX and X, thereby activating the coagulation protease cascades. In response to bacterial lipopolysaccharide (LPS) monocytes transcribe, synthesize and express TF on their surface. We investigated whether LPS-induced TF in human monocytes is mediated by protein kinase C (PKC) activation. The PKC agonists phorbol 12-myristate 13-acetate (PMA) and phorbol 12, 13 dibutyrate (PdBu) were both potent inducers of TF in human monocytes, whereas 4 alpha-12, 13 didecanoate (4 alpha-Pdd) had no such effect. Both LPS- and PMA-induced TF activity were inhibited, in a concentration dependent manner, by three different PKC inhibitors: H7, staurosporine and calphostin C. TF antigen determination confirmed that LPS-induced cell-surface TF protein levels decreased in parallel to TF functional activity under staurosporine treatment. Moreover, Northern blot analysis of total RNA from LPS- or PMA-stimulated monocytes showed a concentration-dependent decrease in TF mRNA levels in response to H7 and staurosporine. The decay rate of LPS-induced TF mRNA evaluated after the arrest of transcription by actinomycin D was not affected by the addition of staurosporine, suggesting that its inhibitory effect occurred at a transcriptional level. We conclude that LPS-induced production of TF and its mRNA by human monocytes are dependent on PKC activation.

Interleukin-10 inhibits endotoxin-induced tissue factor mRNA production by human monocytes

In Gram-negative septic shock, human monocytes synthesize and express on their cytoplasmic membrane tissue factor (TF), a potent activator of the coagulation cascades. The role of TF in triggering disseminated intravascular coagulation (DIC) in these patients appears to be clear. We report the suppressive effect of interleukin-10 (IL-10) on endotoxin-induced TF activity and antigen levels, and on the expression of TF mRNA levels in human monocytes. These results emphasize the potential therapeutic value of this cytokine in septic shock, a condition still associated with a high mortality rate.

Interleukin 4 prevents the induction of tissue factor mRNA in human monocytes in response to LPS or PMA stimulation

Increased expression of tissue factor (TF) procoagulant activity by blood monocytes and tissue macrophages is implicated in a number of thrombotic disorders, as well as in fibrin deposition associated with inflammatory lesions and immunological diseases. We found that interleukin 4 (IL-4), a T lymphocyte-derived cytokine known to regulate a number of monocyte functions, inhibited the production of TF by monocytes in response to endotoxin and phorbol myristate acetate (PMA) in vitro. IL-4 had a concentration-dependent inhibitory effect on functional TF procoagulant activity (PCA) and reduced the binding of an anti-TF antibody, as assessed by flow cytometry analysis. Moreover, IL-4 reduced LPS- and PMA-induced TF mRNA levels. TF mRNA stability was not modified by IL-4 after the arrest of transcription by actinomycin D. We thus conclude that mRNA suppression is mediated by an effect occurring at the transcriptional level. Our results also show that the suppressive effect of IL-4 is independent of an increase in the intracellular concentration of cyclic AMP, another established inhibitor of TF production. Locally produced IL-4 might thus contribute to limiting the consequences of monocyte activation.

Pentoxifylline inhibits the expression of tissue factor mRNA in endotoxin-activated human monocytes

Tissue factor (TF) is a transmembrane glycoprotein which, in association with factor VII(a), is the main activator of coagulation. In illnesses such as Gram-negative endotoxemia, circulating monocytes synthesize and express substantial TF activity, resulting in extensive disseminated intravascular coagulation. We investigated the way in which TF is suppressed by pentoxifylline (PTX), and found that PTX down-regulates immunologic TF expression and specific mRNA production in response to LPS. Since TF mRNA stability is not altered, this effect appears to take place at the transcriptional level.

Involvement of general practitioners in mass screening. Experience of a colorectal cancer mass screening programme in the Calvados region (France)

Good compliance with screening programmes is essential and experience from ongoing studies points to the importance of involving general practitioners (GPs). The aim of this study was to evaluate factors influencing the participation of GPs in a screening programme, as well as acceptance of the test by the population. Fifty GPs were randomly chosen among the 117 practices of three districts in Calvados (France) where haemoccult test-based mass screening for colorectal cancer was underway. Each GP was asked to fill in a personal questionnaire as well as a detailed record for each patient between 45 and 74 years seen in the practice during a 1-week period. The GPs offered the test to 95% of the patients. The overall refusal rate was 7.8%, and was higher in women than in men (9.9% vs 5.9%; P < 0.05). Manual workers had a lower refusal rate than other occupational groups (2.5% vs 8.5%; P < 0.05). The GP's motivation was an important factor in patient compliance: the refusal rate was 5.4% in the case of highly motivated GPs, against 20.0% when the GP was poorly motivated (P < 0.01). GP motivation was higher in urban than in rural areas (P < 0.05) but did not depend on sex, age or the duration or type of practice. According to the GPs, motivating factors were the perceived need for screening, involvement in planning the campaign, and regular feedback. Conversely, a lack of time and the possibility of false-negative results were the most important impediments. This study demonstrates that patient compliance is closely linked to practitioner motivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin-induced tissue factor messenger RNA in human monocytes is negatively regulated by a cyclic AMP-dependent mechanism

Tissue factor (TF) is a transmembrane receptor that serves as the major cofactor for factor VIIa-catalyzed proteolytic activation of factors IX and X. In response to bacterial lipopolysaccharide (LPS), monocytes transcribe, synthesize, and express TF on their surface, thereby conveying to activated monocytes the ability to initiate the blood coagulation protease cascades. Agents that elevate cellular cyclic AMP (cAMP) inhibit the functional expression of TF by LPS-stimulated monocytes. In this study, we investigated the mechanism of this suppression. Northern blot analysis of total RNA from LPS-stimulated monocytes showed a concentration-dependent decrease in TF messenger RNA (mRNA) levels in response to dibutyryl-cAMP (dBt-cAMP). TF mRNA and procoagulant activity were inhibited as early as 1 hour after the addition of dBt-cAMP and the inhibition persisted through 4 hours. Suppression of specific mRNA abundance was also observed with agents, including forskolin and iso-butyl-methyl-xanthine (IBMX), that increase cAMP levels by independent mechanisms. Flow immunocytometric analysis confirmed that cell-surface TF protein levels declined in parallel with TF functional activity. The rate of decay of TF mRNA after the arrest of transcription by actinomycin D was not altered by the addition of dBt-cAMP, IBMX, or forskolin, thus excluding effects on TF mRNA stability. We conclude that elevated cAMP levels suppress TF mRNA by reducing the rate of TF gene transcription.

Procoagulant activity of endotoxin or tumor necrosis factor activated monocytes is enhanced by IgG from patients with lupus anticoagulant

The effect of lupus anticoagulant (LA) positive plasma on the expression of human monocyte procoagulant activity (PCA) was studied. LA positive plasma were able to enhance the endotoxin or TNF alpha induced monocyte associated PCA. The monocyte PCA had the characteristic of tissue factor activity (factor VII, factor X dependence). The enhancement of monocyte PCA could be confirmed using purified LA positive IgG. The stimulating effect was supported by the F(ab')2 fragments.

n-3 polyunsaturated fatty acids raise low-density lipoproteins, high-density lipoprotein 2, and plasminogen-activator inhibitor in healthy young men

The effects of a moderate supplementation in n-3 polyunsaturated fatty acids (PUFAs) were investigated in 36 young healthy adult males. Factors investigated were lipoprotein (including HDL subfractions and apolipoproteins) and hemostasis indexes, assessed by platelet aggregation and plasminogen-activator-inhibitor (PAI) activity. Fat-controlled diets were prescribed, one with and one without a fish-oil supplement (control diet), successively during 3 wk in random order. Total calorie, fat, and cholesterol intakes were similar in the two diets. Triglycerides in serum and very-low-density lipoproteins were lower and high-density-lipoprotein 2 cholesterol was higher with the n-3 PUFA-supplemented diet. These effects as well as a significant decrease in platelet aggregation can be considered beneficial in terms of cardiovascular risk. However, significant increases in low-density-lipoprotein cholesterol and PAI activity occurred and were correlated. This latter effect could be detrimental.

Increased monocyte procoagulant activity independent of the lupus anticoagulant in patients with systemic lupus erythematosus

Monocytes can play a role in the activation of coagulation via increased procoagulant activity (PCA). We investigated the level of monocyte PCA in 19 patients with systemic lupus erythematosus (SLE), given the high rate of thrombotic events in this condition. Nine of these subjects also presented the lupus anticoagulant (LA). The PCA generated by patient monocytes was significantly higher than control values and was identified as tissue factor-like. Moreover, the number of monocytes with membrane-associated D dimer, a parameter which we have shown to be correlated with the PCA expressed in vitro by endotoxin-activated monocytes, was also significantly increased. Serum from both groups of patients (i.e. SLE and SLE + LA) stimulated the generation of PCA by control monocytes. By contrast, purified IgG from both patient groups had the same effect as control IgG on PCA generation by control monocytes. The nature of the stimulating agent in the serum was not identified. In conclusion, increased monocyte PCA may account for the increased incidence of thrombosis in SLE patients, although other, superimposed, factors would appear to exist in SLE + LA patients, given the higher incidence of thrombosis in this subgroup.

Pentoxifylline inhibition of procoagulant activity generated by activated mononuclear phagocytes

When appropriately stimulated, monocytes are able to initiate blood coagulation through the membrane expression of tissue factor. This procoagulant activity is thought to play a role in activating coagulation in response to inflammatory stimuli in vivo. We found that pentoxifylline, a methylxanthine derivative already reported to regulate some monocyte functions, inhibits the procoagulant activity developed by U937 cells and monocytes in vitro in response to endotoxin. This effect was accompanied by an early increase in intracellular levels of cyclic AMP and was mimicked by compounds that induce an increase in the level of cyclic AMP levels. These results suggest that the suppressive effect of pentoxifylline occurs at least in part via an increase in intracellular cyclic AMP levels.

Monocyte procoagulant activity and membrane-associated D dimer after knee replacement surgery

We have recently shown that monocyte membrane-associated cross-linked fibrin derivatives (D dimer) can be evidenced by immunogold staining. Using this method, the procoagulant activity (PCA) expressed in vitro by endotoxin-stimulated monocytes has been found to correlate significantly with the number of D dimer-positive monocytes. The incidence of postoperative thrombosis in patients undergoing total knee replacement has been reported by Stulberg et al to be 57%. Since monocytes can play a role, via increased PCA, in the activation of intravascular coagulation, we sought to determine the level of monocyte PCA ex vivo after knee replacement surgery and its possible correlation with the number of D dimer-positive monocytes. Finally, we examined the possible link between these modifications and the occurrence of postoperative deep vein thrombosis (DVT). The PCA expressed by monocytes with or without suboptimal stimulation, the number of D dimer-positive monocytes and the plasma level of D dimer were measured pre- and post-operatively in 11 patients undergoing total knee replacement. Phlebography was performed on day 10 after surgery. A significant increase in the PCA of stimulated monocytes was observed on day 10 after surgery. Moreover, both the number of D dimer-positive monocytes and the plasma level of D dimer increased significantly post-operatively. The number of D dimer-positive monocytes correlated with both monocyte PCA and the plasma D dimer level. The relation between these parameters is discussed. However, neither monocyte PCA nor the number of D dimer-positive monocytes was found to correlate with the occurrence of deep vein thrombosis.

Binding of an anti D dimer monoclonal antibody to endotoxin-activated monocytes. Demonstration by immunogold-silver staining

Blood monocytes exposed to a variety of stimuli, of which endotoxin is a potent one, produce and express on their membrane a procoagulant activity (PCA) which can trigger the formation of pericellular fibrin. We have developed an immunogold silver method using a monoclonal anti-D dimer antibody to detect the presence of crosslinked fibrin in derivatives on the monocyte membrane. The in vitro PCA of endotoxin-stimulated monocyte was shown to correlate significantly with the number of D dimer-positive monocytes. We suggest that this method could be used to identify activated monocytes expressing increased PCA.