Table 2.

Patient characteristics, intervention, primary outcome, and follow-up time

First author	SIGN quality rating	Year	Location	Study design	Sample size	Mean age, years	Intervention	Primary outcome	Follow-up period
Albi-Feldzer [9]	High quality (++)	2013	France	RCT	236	56	Ropivacaine would infiltration	Pain brief pain inventory score at 3 months	Up to 12 months post-operatively
Amr [10]	Low quality (0)	2010	Egypt	RCT	150	44	Perioperative administration of Venlafaxine or Gabapentin	Acute pain VAS	Up to 6 months post-operatively
Andersen [11]	Acceptable (+)	2015	Denmark	Observational (prospective cohort)	545	61 (median)	Breast cancer surgery for stage I and II disease	Predictive factors for pain experienced 1 year after surgery	Up to 12 months post-operatively
Baudic [12]	Acceptable (+)	2016	France	Observational (prospective)	100	55	Mastectomy or lumpectomy with axillary node dissection	Effect of alexithymia and emotional repression on the development of post-operative pain	Up to 12 months post-operatively
Divella [13]	Acceptable (+)	2020	Italy	Observational	218	55	Conservative breast surgery including excisional biopsy and nipple sparing mastectomy	Describe incidence of chronic pain after breast cancer surgery	Up to 6 months post-operatively
Fujii [14]	Acceptable (+)	2019	Japan	RCT	80	58.15	Pectoral nerve block versus serratus plane block	Rate of pain worse than mild at six post-operative months	Up to 6 months post-operatively
Habib [15]	Acceptable (+)	2019	USA	Observational	124	58	Elective breast cancer surgery	Maximum acute pain score in the first 72 h	Up to 12 months post-operatively
Kang [16]	High quality (++)	2020	Republic of Korea	RCT	185	50.25	Intraoperative low-dose ketamine	Incidence of post-surgical site pain at 3 months after surgery	Up to 6 months post-operatively
Karki [17]	Acceptable (+)	2005	Finland	Observational	110	58.1	Elective breast cancer surgery	Describe the impairments of upper body and limb functions and structures among breast cancer patients	Up to 12 months post-operatively
Karmakar [18]	Acceptable (+)	2014	Hong Kong	RCT	180	52.66	Thoracic paravertebral block	Reduction in the incidence of chronic pain after a modified radical mastectomy when compared with general anaesthesia	Up to 6 months post-operatively
Kendall [19]	Acceptable (+)	2018	USA	RCT	148	49.5	Intraoperative systemic lidocaine	Frequency of chronic post-surgical pain	Up to 6 months post-operatively
Lötsch [20]	High quality (++)	2018	Finland	Observational	1,000	56.7	Breast-conserving surgery or mastectomy and sentinel node biopsy and/or axillary clearance	Identify parameters that predict the persistence of significant pain via supervised machine learning	Up to 36 months post-operatively
Okamoto [21]	Acceptable (+)	2018	Japan	Observational	123	59	Breast cancer surgery under general anaesthesia	Compare the predictive accuracy outcomes of the acute pain trajectory and pain intensity at 1 day after the surgery for pain prevalence at 6 months after the surgery	Up to 6 months post-operatively
Qian [22]	Acceptable (+)	2019	China	RCT	184	46.6	Pre-operative ultrasound-guided multilevel paravertebral blocks	Whether the use of ultrasound-guided multilevel paravertebral blocks with ropivacaine reduced the incidence of postmastectomy chronic pain 3 months after surgery	Up to 6 months post-operatively
Spivey [23]	Acceptable (+)	2018	USA	Observational	216	55.6	Breast surgery with or without known malignancy	Chronic pain at 6 months, collected using the breast cancer pain questionnaire first developed by Gartner et al.	Up to 6 months post-operatively
Tasmuth [24]	Acceptable (+)	1996	Finland	Observational	93	58 (median)	Breast-conserving surgery or mastectomy and/or axillary clearance	How pain and other symptoms develop during the first year after two different types of surgery (breast conservative or not) and how these symptoms are related to the psychological state of the patients	Up to 12 months post-operatively

RCT, randomized controlled trial.