IMPORTANCE: Surgical cancer treatments may be delayed for patients who smoke over concerns for increased risk of complications. Quantifying risks for people who had recently smoked can inform any trade-offs of delaying surgery. OBJECTIVE: To investigate the association between smoking status or smoking cessation time and complications after cancer surgery. DATA SOURCES: Embase, CINAHL, Medline COMPLETE, and Cochrane Library were systematically searched for studies published from January 1, 2000, to August 10, 2023. STUDY SELECTION: Observational and interventional studies comparing the incidence of complications in patients undergoing cancer surgery who do and do not smoke. DATA EXTRACTION AND SYNTHESIS: Two reviewers screened results and extracted data according to the Meta-Analyses of Observational Studies in Epidemiology (MOOSE) reporting guidelines. Data were pooled with a random-effects model and adjusted analysis was performed. MAIN OUTCOMES AND MEASURES: The odds ratio (OR) of postoperative complications (of any type) for people who smoke currently vs in the past (4-week preoperative cutoff), currently smoked vs never smoked, and smoked within shorter (2-week cutoff) and longer (1-year cutoff) time frames. RESULTS: The meta-analyses across 24 studies with a pooled sample of 39 499 participants indicated that smoking within 4 weeks preoperatively was associated with higher odds of postoperative complications compared with ceasing smoking for at least 4 weeks (OR, 1.31 [95% CI, 1.10-1.55]
n = 14 547 [17 studies]) and having never smoked (OR, 2.83 [95% CI, 2.06-3.88]
n = 9726 [14 studies]). Within the shorter term, there was no statistically significant difference in postoperative complications between people who had smoked within 2 weeks preoperatively and those who had stopped between 2 weeks and 3 months in postoperative complications (OR, 1.19 [95% CI, 0.89-1.59]
n = 5341 [10 studies]), although the odds of complications among people who smoked within a year of surgery were higher compared with those who had quit smoking for at least 1 year (OR, 1.13 [95% CI, 1.00-1.29]
N = 31 238 [13 studies]). The results from adjusted analyses were consistent with the key findings. CONCLUSIONS AND RELEVANCE: In this systematic review and meta-analysis of smoking cessation and complications after cancer surgery, people with cancer who had stopped smoking for at least 4 weeks before surgery had fewer postoperative complications than those smoking closer to surgery. High quality, intervention-based evidence is needed to identify the optimal cessation period and inform clinicians on the trade-offs of delaying cancer surgery.