A study of 155 cancer-related clinical trials shows that few asked participants about their tobacco use, limiting our understanding of how continued use may affect treatments and outcomes.

Researchers call for standardized assessments to better understand the impact of tobacco on treatment.

Although tobacco use is a well-established risk factor for multiple cancers—and some evidence shows it can affect the course of disease and the effectiveness of treatment—many cancer-related clinical trials fail to take it into account, researchers have reported in the Journal of Clinical Oncology. Adding structured assessments of tobacco use to trials will improve understanding of its effects on treatment, they say.

Researchers representing 4 institutions reviewed protocols and enrollment forms for the 155 clinical trials in the National Cancer Institute's (NCI) Clinical Trials Cooperative Group Program that were accruing patients as of June 3, 2011. Only 29% of the clinical trials asked about tobacco use during study enrollment. Just 4.5% of the trials assessed tobacco use during follow-up appointments. None of the trials assessed nicotine dependence, asked whether participants wanted to stop using tobacco, or mentioned tobacco-cessation programs.

“It's disappointing,” says Graham Warren, MD, PhD, assistant professor of radiation oncology at Roswell Park Cancer Institute in Buffalo, NY, and the study's senior author. Many of the trials that did query tobacco use failed to ask about the type, amount, and duration of tobacco use. Instead, they only posed limited questions about whether participants are current or past users, “so saying that 29% assessed tobacco use is extremely generous,” he adds.

“This is really a missed opportunity,” says Michele Bloch, MD, PhD, acting chief of NCI's Tobacco Control Research Branch in its Division of Cancer Control and Population Sciences. Over the past few decades, researchers have gathered extraordinary amounts of data about how tobacco use causes cancer and other diseases, but what's missing, she says, is a complete, accurate picture of how continued tobacco use affects cancer treatment.

“Increasingly we realize the potential role that continued tobacco use plays in cancer outcomes,” says Bloch. “Many studies show that patients who quit have better treatment outcomes, develop fewer second cancers, and enjoy better quality of life than those who continue to use tobacco, but more and better data are still needed.”

“Tobacco use may have an even more pronounced impact than we currently realize,” Warren says, “but we don't know because we don't ask about it.”

Continuing to use tobacco after a cancer diagnosis seems to “change the intrinsic sensitivity of cancer cells to traditional cancer treatments, such as chemotherapy and radiation therapy,” explains Warren. In addition to altering drug metabolism, chemicals in tobacco and tobacco smoke may activate new oncogenic pathways, increase tumor cell migration and metastasis, and promote angiogenesis.

The study team noted that “the only method for evaluating the potential effects of tobacco use on cancer treatment is to incorporate structured and repeated tobacco assessments into clinical trials design.”

Warren says that several groups are working on assessment tools, and that creating a standard set of questions would allow comparison of results across trials. “We would like to help make that happen,” says Bloch.