Table 4.

Studies evaluating warfarin and cancer risks.

Study	Country	Study design	Population	N	Follow-up time	Cancer types	Comparison	Results (95%CI)
Schulman 2000 [37, 38]	Sweden	Post-hoc analysis of RCT	First episode of VTE	419 Warfarin for 6 weeks 435 Warfarin for 6 months	8 years	Any	Warfarin 6 weeks vs. 6 months	OR 1.6 (1.1 – 2.4) * Difference mainly due to urogenital cancers: OR 2.5 (1.3-5.0)
Taliani 2003 [47, 49]	Italy	Post-hoc analysis of RCT	First episode of VTE	210 Warfarin for 3 months 219 Warfarin for 12 months	3.6 years	Any	Warfarin 3 months vs. 12 months	RR 0.71 (0.36 – 1.41)
Blumentals 2004 [48]	USA	Retrospective case-control (single cohort)	White male patients seen at hospital	330 Cases 1293 Controls	NR	Bladder	Warfarin vs. no warfarin	OR 1.27 (0.85 – 1.89)
Tagalakis 2007 [39]	Canada	Retrospective case-control (Administrative database)	Men age ≥50	19412 Cases 116470 Controls	NR	Urogenital	Warfarin (4-year use) vs. no warfarin	IRR 0.80 (0.65 – 0.99) * Only significant in prostate cancer: IRR 0.67 (0.53 – 0.86) *
Pengo 2011 [40]	Italy	Retrospective cohort (Administrative database)	Age 65-90 without prior cancer or VTE	3231 Warfarin 72777 No warfarin	8.2 years	Any	Warfarin vs. no warfarin	HR 0.88 (0.80 – 0.98) * Only significant in prostate cancer: HR 0.69 (0.50 – 0.97) *
Ahern 2011 [43]	USA	Retrospective cohort (Administrative database)	Danish population	8724 Heart valve replacement 87240 No heart valve replacement	NR	Any	Warfarin vs. no warfarin (heart valve replacement was used a proxy for warfarin)	No significant difference in all cancers
Pottegard 2013 [44]	Denmark	Retrospective case-control (Administrative database)	Danish population	238196 Cases 1713176 Controls	NR	Any	Warfarin for ≥ 3 years vs. no warfarin	OR 1.11 (1.07 – 1.15) Only significant in prostate cancer: OR 0.94 (0.76 – 1.17) *
Blanclapierre [45]	Canada	Retrospective case-control (single cohort)	Men age ≤75	1588 Cases 1618 Controls	NR	Prostate	Warfarin vs. no warfarin	OR 0.76 (0.50 – 1.16)
Kinnunen 2016 [50]	Finland	Retrospective cohort (Administrative database)	Men age 55 – 67	12747 Warfarin 55674 No anticoagulants	NR	Prostate	Warfarin vs. no anticoagulants	HR 1.11 (1.01 – 1.22) * (risk only elevated in low-dose short-term use)
Haaland 2017 [41]	Norway	Retrospective cohort (Administrative database)	Age >50	92942 Warfarin 1163783 No warfarin	NR	Any	Warfarin for ≥ 2 years vs. no warfarin	IRR 0.84 (0.2-0.86) * Significant in many cancers including lung, breast, and prostate.
Kristensen 2019 [46]	Denmark	Retrospective cohort (Administrative database)	Men age 40 – 85	38832 Cases 388320 Controls	NR	Prostate	VKAs for ≥ 3 years vs. no VKA	OR 1.03 (0.97 – 1.10)
Parker 2020 [42]	Sweden	Retrospective case-control (Administrative database)	Men	31591 Cases 156802 Controls	NR	Prostate	Warfarin vs. no warfarin DOACs vs. no DOACs	OR 0.92 (0.88 – 0.96)* OR 0.97 (0.90 – 1.06)