Smoking history can both increase the risk of cancer and create a hypoxic environment within the body, leading to poor outcomes, including less-effective treatment, among patients who undergo radiotherapy.
Being either a current or former smoker was linked to a greater likelihood of adverse outcomes following adjuvant radiotherapy (RT) for breast cancer, according to review results published in Cancer Treatment and Research Communications.
With there being plenty of evidence to link smoking history and both cancer risk and diagnosis, the authors of the present review focused on whether former and current cigarette smokers were also more likely to experience adverse outcomes following RT. They searched Ovid MEDLINE, Cochrane Central Register of Controlled Trials, and Embase Classic and Embase for studies published between 1947 and January 2019, using such keywords as breast cancer, cigarette smoking, radiotherapy, and outcomes.
Seventy-three articles were included in the authors’ review, which evaluated outcomes following adjuvant RT for breast cancer in current and former smokers. The authors divided these outcomes into 6 categories:
Overall, 198 outcomes were observed between the patients with a smoking history and never-smokers, and 41% were considered significant.
Of the 28 included studies that examined the association between smoking, RT, and skin reactions, skin toxicity was seen in 50% of the patients with a smoking history, which led to significantly worse outcomes after treatment (P < .05) compared with nonsmokers. Greater likelihoods of edema, telangiectasia, breast pain and sensitivity, pigmentation, and breast deformation were also reported.
Eight of the review studies looked at the influence of smoking history on breast reconstruction outcomes after RT. Six of these reported capsular contracture, reconstruction failure, and complications to be significant (P ≤ .05), with one also reporting a greater rate of major complications in smokers compared with nonsmokers (P = .003). A higher risk of tissue expander extrusion was associated (odds ratio [OR], 3.18) with smoking in another study.
The link between CV health and smoking history was evaluated, too, in 8 studies, with 3 reporting more CV events post RT in ever-smokers. However, one of these studies also showed a 2.2-times greater HR for adverse outcomes after RT when both CV health and smoking history (HR, 3.04; 95% CI, 2.03-4.55) were taken into account vs no smoking history (HR, 1.34; 95% CI, 0.94-1.91). Cardiotoxicity and left ventricular ejection fraction below 55% were also reported more often in smokers compared with nonsmokers.
Among the 15 articles reporting on pulmonary function changes, radiation pneumonitis was reported in 9, but this risk was not deemed significant. Meanwhile, RT-induced bronchiolitis obliterans were shown to be more common in patients who smoked (OR, 3.09; 95% CI, 1.01-9.48), and smokers were more likely to have “experienced the largest negative change in forced expiratory volume,” at —8.5% vs –4.6% in nonsmokers.
For the 11 articles in the review that examined secondary carcinomas, results from just 1 study showed a significantly higher risk of breast cancer recurrence compared with never smokers (HR, 6.69; P = .002). Having a smoking history was much more often associated with developing secondary lung cancer, and this risk was shown in one of the studies to be 1.7-times greater in patients who smoked 1 or more packs per day (OR, 46.91) vs those who smoked less than 1 pack (OR, 27.40)
Results from the 3 articles that examined mortality showed both a slightly higher risk of mortality for smokers vs nonsmokers (HR, 1.25; 95% CI, 1.06-1.47; P < .05) following RT, as well as a significant difference (HR, 1.11; 95% CI, 0.52-2.37, vs HR, 0.82; 95% CI, 0.42-1.61, respectively).
“None of the articles in this review reported better outcomes among smokers than never smokers,” the authors concluded. “Cigarette smoking can pose a higher risk of posttreatment complications that can influence an individual’s quality of life, survival rate, and/or recurrence risk. Whether patients who have a history of smoking or smoked during treatment are at similar risk of adverse events to patients who continue to smoke remains unclear.”
Emphasizing smoking cessation programs, informing patients of the potential risks associated with smoking, providing in-hospital patient education, and linking to care are all suggested as possible solutions for individuals to learn about the elevated risk for cancer and adverse treatment outcomes that may accompany their decision to smoke.
Wong G, Lam E, Karam I, et al. The impact of smoking on adjuvant breast cancer radiation treatment: a systematic review. Cancer Treat Res Commun. Published online June 20, 2020. doi:10.1016/j.ctarc.2020.100185