Smoking May Increase Risk of Second Primary Cancer

Smoking may put smokers at an increased risk of developing cancer twice.

Survivors of several cancer types, including kidney cancer, are at an increased risk for developing a second smoking-associated cancer if they smoked cigarettes prior to their first cancer diagnosis, results of a large study published in the Journal of Clinical Oncology indicated.

Specifically, patients with kidney cancer who smoked more than 20 cigarettes at baseline had a fivefold increased risk for developing a second smoking-associated cancer compared with survivors of the same cancer who never smoked. 

“As the number of cancer survivors continues to grow, understanding risk factors for second cancers is crucial,” study author Meredith S. Shiels, PhD, MHs, of the National Cancer Institute told Cancer Network. “We have shown that pre-diagnostic smoking among survivors of smoking-related cancers is associated with an increased risk of developing a new, second smoking-related cancer.”

Sheils and colleagues pooled data from five large trials that included 2,552 patients with stage I lung cancer, 6,386 with bladder cancer, 3,179 with kidney cancer, and 2,967 with head and neck cancer. They were examining data to see if an association existed between prediagnostic smoking status and risk for a second smoking-associated cancer.

Baseline smoking was higher among patients diagnosed with stage I lung (41%), bladder (20%), kidney (15%), and head and neck cancers (33%) compared with other participants.

Compared with those participants who had never smoked, smoking 20 cigarettes or more per day at the time of their first diagnosis was associated with an increased risk of second smoking-associated cancers in survivors of stage I lung (HR = 3.26; 95% CI, 0.92-11.6), bladder (HR = 3.67; 95% CI, 2.25-5.99), head and neck (HR = 4.45; 95% CI, 2.56-7.73), and kidney cancers (HR = 5.33; 95% CI, 2.55-11.1).

Sheils said that these results were not surprising given the strong associations between cigarette smoking and cancer risk. She added that “this is the largest study to date to address the association between smoking and second smoking-related cancer risk among cancer survivors.”

The data from the analysis also showed that risk for a second smoking-related cancer increased with increasing pack-years smoked at baseline for kidney and head and neck cancers, but not for stage I lung or bladder cancer survivors. In addition, among former smokers at baseline, the time since quitting was inversely associated with increased second smoking-associated cancer risk for bladder, kidney, and head and neck survivors.

“Smoking is the leading cause of preventable illness in the United States,” Sheils said. “All smokers can benefit from quitting. Health care providers should emphasize the importance of quitting to all patients, including cancer survivors.”

Smokers who need help quitting should talk to their physicians or contact the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT.