Many Lung Cancer Patients Stopped Smoking Years Before Diagnosis

Norra MacReady

July 14, 2010

July 14, 2010 (Los Angeles, California) — Much of what people think they know about smoking and lung cancer might be wrong, according to findings presented here at the 11th International Lung Cancer Conference.

For example, many if not most patients with a history of smoking quit decades before. In a retrospective study of 626 people with lung cancer treated at a tertiary-care facility in Southern California, 482 (77%) had a history of smoking. Of those, only 71 patients (14.7%) were still smoking at the time of their diagnosis. Of the remaining 411 patients, 245 (60%) had not smoked for a mean of 18 years, 8 of whom had quit 51 to 60 years earlier. The other 166 (40%) had stopped smoking within 10 years of their diagnosis.

"Sixty percent of our cohort developed lung cancer despite doing the right thing by stopping smoking over 1 decade ago," according to the researchers.

These findings contradict the popular perception that most people with lung cancer are ongoing smokers who did not kick the habit until cancer symptoms appeared, the researchers note. The team was led by Cindy Mong, MD, a hematology-oncology resident at the UCLA David Geffen School of Medicine at the University of California, Los Angeles.

Other research has shown that the risk for lung cancer plummets by 50% in the first 15 years after quitting smoking, but "the risk never drops to that of nonsmokers," they warned.

Different Histologies

There was a strong relation between time since smoking cessation and tumor cell histology. Patients were much more likely to have adenocarcinoma if more than 21 years had elapsed since they last smoked (P = .0005), whereas squamous cell carcinoma was more prevalent in current smokers (15.6% of current smokers vs 8.3% of former smokers; P = .028). The prevalence of adenocarcinoma also varied inversely with the number of pack-years smoked (P < .0001).

If anything, patients in this study fared somewhat better than patients in the United States in general, the researchers say. They cite 2008 data from the Centers for Disease Control and Prevention (CDC) showing that only 16% of people in the general population with lung cancer are diagnosed with localized disease, compared with 59% of patients in their study.

According to the CDC data, 41% of patients were diagnosed with stage 3 or 4 disease, compared with 26% of the study population. In 1995, California passed one of the first antismoking laws in the nation when it banned smoking in enclosed workspaces. This might have encouraged more people to quit smoking than in other parts of the country and might help account for the preponderance of patients in the earlier stages of cancer.

Yet lung cancer remains something of a poor relation among the different cancer types, Dr. Mong said. From 1975–77 to 1996–2003, 5-year survival from breast cancer rose from 75% to 89%. Outcomes for prostate cancer were even more impressive, rising from 69% to 99% in the same time period. Lung cancer 5-year survival rates, however, went from 13% to a still-dismal 16%.

Worldwide, lung cancer is the number 1 cancer killer, but it "suffers from poor outcomes partly as a result of disproportionately low federal research, compared with breast, colon, and prostate cancer research," the researchers note.

Lung cancer suffers from a stigma.

"Lung cancer suffers from a stigma because most people assume that the patients did it to themselves," said David R. Gandara, MD, professor of medicine and associate director of clinical research, Division of Hematology and Oncology, University of California, Davis, School of Medicine.

However, that perception is changing rapidly, and funding for lung cancer research is growing, added Dr. Gandara, who was not involved in this study. "Although smoking cessation is important, it is not the total answer. One third of lung cancer patients have never smoked and have never been exposed to second-hand smoke."

Identifying the cause of these malignancies is now the focus of intense interest among investigators. "Is it viral? Is it something else? We still don't know," Dr. Gandara said.

The investigators and Dr. Gandara have disclosed no relevant financial relationships.

11th International Lung Cancer Conference (ILCC): Poster 4. Presented July 10, 2010.

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