Smoking cessation after cancer diagnosis reduces the risk of severe cancer pain: A longitudinal cohort study.

BACKGROUND: Whether abstinence from smoking among cancer patients reduces cancer pain is still unclear. Opioids can act as a surrogate index for evaluating the incidence of severe cancer pain in countries where opioid abuse is infrequent. This study aimed to investigate whether changed smoking behavior after cancer diagnosis influences the incidence of severe cancer pain as determined by strong opioid use. METHODS: Using a large Japanese insurance claims database (n = 4,797,329), we selected 794,702 insured employees whose annual health checkup data could be confirmed ≥6 times between January 2009 and December 2018. We selected 591 study subjects from 3,256 employees who were diagnosed with cancer pain and had health checkup data at the year of cancer pain diagnosis. RESULTS: A significantly greater proportion of patients who continued smoking after cancer diagnosis ("current smoker", n = 133) received strong opioids (36.8%) compared with patients who had never smoked or had stopped before cancer diagnosis ("non-smoker", n = 383, 20.6%; p<0.05) but also compared with patients who had quit smoking after cancer diagnosis ("abstainer:", n = 75, 24.0%; p<0.05). In multivariable Cox proportional hazards regression analysis, abstainers had a significantly lower risk of receiving strong opioids than current smokers (hazard ratio: 0.57, 95% CI: 0.328 to 0.997). These findings were consistent across multiple sensitivity analyses. CONCLUSION: Our study demonstrated that patients who quit smoking after cancer diagnosis have a lower risk of severe cancer pain. This information adds clinical incentives for improving quality of life among those who smoked at the time of cancer diagnosis.