Effects of a self-determination theory-based smoking cessation intervention plus instant messaging via instant messaging for smokers with cancer: A randomized controlled trial.

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Background: Continued smoking after a cancer diagnosis is associated with increased all-cause mortality and reduced treatment efficacy, yet many patients persist in smoking. This study evaluated the effectiveness of a self-determination theory–based smoking cessation intervention, supplemented with instant messaging, in helping smokers with cancer quit smoking. Methods: We conducted an assessor-blinded, multicenter randomized controlled trial involving 1,448 smokers with cancer attending outpatient clinics across five major acute care hospitals in Hong Kong. Participants in the intervention group received brief advice (5–8 minutes) from research nurses and selected their preferred quit schedule (immediate or progressive). For the first 6 months, they received smoking cessation advice via instant messaging weekly for 3 months and then monthly, plus four educational videos; those choosing progressive quitting also received a smoking reduction leaflet. Control participants received brief advice recommending immediate cessation, along with instant messaging containing general health advice on the same schedule. The primary outcome was biochemically validated smoking abstinence at 6 months, confirmed by both saliva cotinine and expired-air carbon monoxide levels. Results: Participants (N = 1448) included 1316 men (90.9%); the mean (SD) age at baseline was 63.0 (10.8) years. Among participants who self-reported abstinence at 6 months, 21.9% (69 of 315) had biochemical validation by both an exhaled carbon monoxide test and a saliva cotinine test. Compared with the control group, the intervention group had statistically higher biochemically validated abstinence at 6 months: 6.2% (45 of 724) vs 3.3% (24 of 724) ( P = 0.01), with an adjusted relative risk of 1.94 (95% CI, 1.50-2.51; P < 0.001). The intervention group also had higher self-reported quit rates at 6 months (26.2% [190 of 724] vs 17.3% [125 of 724], P < 0.001), with adjusted RR of 1.50 (95% CI, 1.32-1.70; P < 0.001). Conclusions: This brief, low-cost intervention grounded in self-determination theory significantly improved biochemically validated quit rates among smokers with cancer in outpatient settings. If implemented routinely, it could represent a scalable, cost-effective approach to promote smoking cessation in this high-risk population. Clinical trial information: NCT05643469 .