Cigarette Smoking Before Diagnosis of First Cancer Is Associated With Increased Risk of Second Cancers
In a study reported in the Journal of Clinical Oncology, Shiels et al found that prediagnostic smoking among survivors of stage I lung cancer or bladder, kidney, or head/neck cancer was associated with increased risk of second lung, bladder, kidney, and head and neck cancer.
Study Details
The study involved pooled data from 2,552 patients with stage I lung cancer, 6,386 with bladder cancer, 3,179 with kidney cancer, and 2,967 with head/neck cancer surviving ≥ 5 years after diagnosis from five cohort studies. Risk for second cancers were compared for never-smokers vs current smokers of ≥ 20 and < 20 cigarettes per day at diagnosis and former smokers of ≥ 20 and < 20 per day at diagnosis.
Second primary lung, bladder, kidney, or head/neck cancers occurred in 80 (3.1%) of those with lung cancer, 385 (6.0%) of those with bladder cancer, 139 (4.4%) of those with kidney cancer, and 262 (8.8%) of those with head/neck cancer (5-year cumulative incidence 3%–8%).
Risk of First Cancer
The prevalence of current smoking at baseline was 41% in patients with stage I lung cancer, 20% for bladder cancer, 15% for kidney cancer, and 33% for head/neck cancer. Compared with never-smokers, current smoking of ≥ 20 cigarettes per day at diagnosis had a hazard ratio (HR) for second smoking-related cancers of 5.41 (95% confidence interval [CI] = 5.23–5.61). Hazard ratios were 3.72 for current smokers smoking < 20 cigarettes per day, 2.35 for former smokers who smoked ≥ 20 per day, and 1.48 for former smokers who smoked < 20 per day.
Risk of Second Cancer
Compared with never smoking, current smoking of ≥ 20 cigarettes per day at diagnosis was associated with increased second smoking-associated cancer risk among survivors of stage I lung (HR = 3.26, 95% CI = 0.92–11.6; P = .002 for trend), bladder (HR = 3.67, 95% CI = 2.25–5.99; P < .001 for trend), kidney (HR = 5.33, 95% CI = 2.55–11.1; P < .001 for trend), and head/neck cancers (HR = 4.45, 95% CI = 2.56–7.73; P < .001 for trend).
Individual hazard ratios for second cancer were significant among patients with bladder cancer (2.81), kidney cancer (3.44), and head/neck cancer (2.89) who currently smoked < 20 cigarettes per day; for patients with bladder (2.12), kidney (4.08), or head/neck cancer (2.97) who were former smokers who smoked ≥ 20 per day; and for those with bladder (1.84) or kidney cancer (1.90) who were former smokers who smoked < 20 per day.
Among former smokers at baseline, time since quitting was significantly inversely associated with increased second cancer risk among those with initial bladder (P < .001 for trend), kidney (P = .002 for trend), and head/neck cancers (P < .001 for trend) but not stage I lung cancers (P = .99 for trend).
The investigators concluded: “Understanding risk factors for second cancers among cancer survivors is crucial. Our data indicate that cigarette smoking before first cancer diagnosis increases second cancer risk among cancer survivors, and elevated cancer risk in these survivors is likely due to increased smoking prevalence. The high 5-year cumulative risks of smoking-associated cancers among current smoking survivors of stage I lung, bladder, kidney, and head/neck cancers highlight the importance of smoking cessation in patients with cancer.”
Meredith S. Shiels, PhD, MHS, of the National Cancer Institute, is the corresponding author for the Journal of Clinical Oncology article.
The study was supported by the National Cancer Institute. Laura Beane Freeman, PhD, reported employment, leadership, and stock or other ownership with Procter & Gamble.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
