Summary of findings for the main comparison. LMWH initial treatment compared to UFH initial treatment in people with cancer with VTE.

LMWH initial treatment compared to UFH initial treatment in people with cancer with VTE
P: people with cancer and a confirmed diagnosis of VTE S: inpatient/outpatient I: LMWH initial treatment C: UFH initial treatment
Outcomes	No of participants (studies)	Certainty of the evidence (GRADE)	Relative effect (95% CI)	Anticipated absolute effects* (95% CI)
				Risk with UFH initial treatment	Risk difference with LMWH initial treatment
Mortality follow‐up: 3 months	418 (5 RCTs)	⊕⊕⊕⊝ Moderate1	RR 0.66 (0.40 to 1.10)	Study population
				168 per 1000	57 fewer per 1000 (101 fewer to 17 more)
Recurrent VTE follow‐up: 3 months	422 (3 RCTs)	⊕⊕⊕⊝ Moderate2	RR 0.69 (0.27 to 1.76)	Study population
				96 per 1000	30 fewer per 1000 (70 fewer to 73 more)
*The risk in the intervention group (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; LMWH: low molecular weight heparin; RCT: randomized controlled trial; RR: risk ratio; UFH: unfractionated heparin; VTE: venous thromboembolism.
GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

¹95% CI was consistent with the possibility for important benefit (101 per 1000 absolute reduction) and possibility of important harm (17 per 1000 absolute increase), including 59 events in total.

²95% CI was consistent with the possibility for important benefit (70 per 1000 absolute reduction) and possibility of important harm (73 per 1000 absolute increase), including only 34 events in total.