Summary of findings 8. Vitamin K antagonists versus placebo or no thromboprophylaxis.
| VKA compared with placebo or no thromboprophylaxis for primary thromboprophylaxis in ambulatory cancer patients receiving chemotherapy | |||||||
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Patient or population: ambulatory cancer patients receiving chemotherapy Settings: outpatient clinics Intervention: VKA Comparison: placebo or no thromboprophylaxis | |||||||
| Outcomes | Relative effect (95% CI) | Illustrative comparative risks* (95% CI) | Differenceb (95% CI) | No of participants (studies) | Certainty of the evidence (GRADE) | What it means | |
| Assumed riska | Corresponding risk | ||||||
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With placebo or no thromboprophylaxis Number of events per 1000 participants |
With VKA Number of events per 1000 participants |
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Symptomatic VTE Follow‐up: mean 6 months |
RR 0.15 (0.02 to 1.2) | Intermediate‐risk populationc | 37 per 1000 fewer events (43 fewer to 9 more) | 311 (1) | ⊕⊕⊝⊝ Lowd | VKA may reduce the incidence of symptomatic VTE in breast cancer. | |
| 44 per 1000 | 7 per 1000 (1 to 53) | ||||||
|
Major bleeding Follow‐up: mean 6 months |
RR 3.82 (0.97 to 15.04) | Intermediate‐risk populationc | 18 per 1000 more events (0 fewer to 88 more) | 994 (4) | ⊕⊕⊝⊝ Lowe | VKA may increase the incidence of major bleeding in breast cancer and small‐cell lung cancer. | |
| 6 per 1000 | 24 per 1000 (6 to 95) | ||||||
|
Symptomatic PE Follow‐up: mean 6 months |
RR 1.05 (0.07 to 16.58) | Intermediate‐risk populationc | 0 per 1000 fewer events (6 fewer to 101 more) | 311 (1) | ⊕⊝⊝⊝ Verylowf | We have very little confidence in the estimated effect of VKA on symptomatic PE in breast cancer. | |
| 6 per 1000 | 7 per 1000 (0 to 108) | ||||||
|
Symptomatic DVT Follow‐up: mean 6 months |
RR 0.08 (0 to 1.42) | Intermediate‐risk populationc | 35 per 1000 fewer events (38 fewer to 16 more) | 311 (1) | ⊕⊕⊝⊝ Lowd | VKA may reduce the incidence of symptomatic DVT in breast cancer. | |
| 38 per 1000 | 3 per 1000 (0 to 54) | ||||||
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Any VTE Follow‐up: NA |
NAg | Intermediate‐risk populationc | NA | NA | NA | We do not know how VKA affects any VTE across different cancer types. | |
| NA | NA | ||||||
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1‐year overall mortality Follow‐up: NA |
NAg | Intermediate‐risk populationc | NA | NA | NA | We do not know how VKA affects 1‐year overall mortality across different cancer types. | |
| NA | NA | ||||||
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Clinically relevant bleeding Follow‐up: NA |
NAg | Intermediate‐risk populationc | NA | NA | NA | We do not know how VKA affects clinically relevant bleeding across different cancer types. | |
| NA | NA | ||||||
| *The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; DVT: deep vein thrombosis; NA: not applicable; PE: pulmonary embolism; RR: risk ratio; VKA: vitamin K antagonists; VTE: venous thromboembolism. | |||||||
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GRADE Working Group grades of evidence High certainty: further research is very unlikely to change our confidence in the estimate of effect. Moderate certainty: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low certainty: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low certainty: we are very uncertain about the estimate. | |||||||
aThe assumed risk was calculated from the medium observed control group risk across the trials. bDifference calculated as the absolute risk difference between the assumed risk and corresponding risk, expressed per 1000. cIntermediate‐risk population refers to the median observed risk to experience symptomatic VTE in the trials contributing to the analyses (44 per 1000). Rates between 2% and 7% are considered intermediate risk (Khorana 2008). dDowngraded two levels because of imprecision, risk of publication bias (only 1/4 trials reported on this outcome), and potential risk of attrition bias, see Characteristics of included studies table. eDowngraded two levels because of imprecision and potential attrition bias in 2/4 trials. fDowngraded three levels because of imprecision (two levels), the risk for publication bias, as only 1/4 trials reported on this outcome, and potential attrition bias, see Characteristics of included studies table. gNo trials contributed to this outcome.