ADDITIONAL SUMMARY OF FINDING [Explanation]

Should regional anaesthesia or conventional pain control be used to prevent persistent pain following breast cancer surgery
Patient or population: women with breast cancer undergoing elective surgery Settings: cancer, community and university hospitals in Europe, China and North America Intervention: various regional anaesthesia techniques including paravertebral block, nerve blocks or local infiltration Comparison: conventional pain control
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence Comments (GRADE)	Comments
	Assumed risk	Corresponding risk
	Conventional pain control	Paravertebral block
Persistent pain 3 to 12 months after breast cancer surgery (We def ined persistent postsurgical pain as new pain that did not exist before the operation, measured using dif ferences in scores based on validated pain scales; patient inter-view between 3 to 12 months af ter surgery.)	Study population		OR 0.43 (0.28 to 0.68)	1297 (18 studies)	⊕⊕⊕⚪ low1,2	Conventional pain control with opioids and NSAID was the comparator Event rates of persistent pain af ter breast cancer were reported around 30% Pooling all studies, regional anaesthesia may prevent persistent pain after breast surgery in one out of every seven women. Limiting the analysis to paravertebral block, the number of women needed to treat for one person to benef it was 11
	427 per 1000	239 per 1000 (162 to 340)
	Low
	200 per 1000	95 per 1000 (61 to 147)
	High
	600 per 1000	387 per 1000 (281 to 509)
Adverse effects of paravertebral block for breast cancer surgery	See comment	See comment	Not estimable	-	See comment	Adverse ef fects of regional anaesthesia after breast surgery were not systematically reported and due to their low f requency are better investigated in registries

^*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; NSAID: nonsteroidal anti-inf lammatory drugs; OR: odds ratio

GRADE Working Group grades of evidence

High quality: we are very confident that the true effect lies close to that of the estimate of the effect.

Moderate quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different.

Low quality: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of effect, but there is a possibility that it is substantially different.

Very low quality: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect

¹We downgraded quality of evidence by one level because conclusions may be considerably weakened by performance bias, shortcomings in allocation concealment, considerable attrition and incomplete outcome data.

²We downgraded quality of evidence by one level because there was evidence of heterogeneity. The ef fect estimates were contingent on the type of surgery and the anaesthesia intervention.