Background:
Previous studies indicate that quitting smoking significantly improves health-related quality of life (QOL) in patients with lung and head and neck cancer. However, few prospective studies have investigated the role of smoking status on QOL across patients diagnosed with a wide range of cancers. The aim of the present study was to examine quality of life (depression, pain, and fatigue) changes over time as a function of smoking status.

Methods:
Participants were 351 cancer patients (e.g., gynecological, breast, thoracic, head and neck, genitourinary, hematological, cutaneous) who reported smoking abstinence within the previous 120 days. Smoking status and QOL (depression, pain severity, fatigue severity, and fatigue interference) were assessed at baseline, 2, 6, and 12 month follow-ups. Within a Structural Equation Modeling (SEM) framework, growth curve models with smoking status as a time varying covariate were employed to examine the effect of smoking status change in QOL measures over time. Baseline demographics (e.g., sex, income) and smoking history (e.g., nicotine dependence) were controlled.

Results:
Overall, models with both time-varying covariates (smoking status) and time-invariant covariates (demographics, nicotine dependence) were good-to-excellent fits with the data. Smoking status had a main effect and an interaction with time upon depression and pain severity. For fatigue severity and fatigue interference, smoking status interacted with time, i.e., smoking abstinence at the 6 and 12 months follow-ups were associated with lower fatigue scores across the estimated growth curve.

Conclusions:
These results extend previous findings showing that QOL improves in cancer patients who quit smoking. Specifically, patients who quit smoking experience a greater reduction in depression and pain levels at all time points, and the reduction increases over time. In the case of fatigue, the results suggest that patients experience the greatest improvement with longer (≥ 4 months) abstinence.