Within the next decade or so, more women than men could face a lung cancer diagnosis, even though it's thought today that more men contract the disease, says a University of Michigan researcher.

Closing the Gap Gregory Kalemkerian, MD, headed a study published in the journal Chest this month that suggests that the incidence of lung cancer in women "has reached a plateau", thus narrowing the gap between men and women.1 "Although the incidence of lung cancer in men has been declining for years, most studies have reported a continued increase in incidence in women," wrote Kalemkerian and his team. But while there appear to be gender-based differences both in survival and in signs and symptoms in lung cancer, information about this in the medical literature is conflicting, they pointed out. Ties to Lung Fibrosis Lung cancer is the second most common type of cancer diagnosed in women in the United States today, according to the study authors. In 2003, it was estimated that nearly half of new lung cancer cases and 44% of related deaths would occur in women, the investigators wrote.1 Lung cancer is a frequent complication in people with idiopathic pulmonary fibrosis (IPF),2 a disease characterized by scarring in the lungs. One study of a group of IPF patients found that a third of them had contracted lung cancer, with about 66 percent of them having a smoking history of over 40 years.3 IPF affects an estimated 5 million people around the world, with about 200,000 alone in the United States. The scarring causes lung tissue to become thicker, which in turn, causes an irreversible loss of the tissue's ability to transfer oxygen to the bloodstream. Symptoms include shortness of breath, particularly with exertion; chronic cough; fatigue and weakness; chest discomfort; loss of appetite; and rapid weight loss.4 IPF can be associated in some cases with pulmonary hypertension.5 More Younger Women Contract Lung Cancer In hopes of better understanding the gender differences in the incidence and epidemiology of lung cancer, Kalemkerian and his colleagues analyzed information on demographics, cancer stage, lung health, initial therapy, and survival odds related to 228,572 lung cancer patients that was entered into a National Cancer Institute-sponsored, population-based cancer database between 1975 and 1999. Overall, they found that nearly 36 percent of the patients were female, the median age at diagnosis was 66 years for both men and women, and women accounted for about 41 percent of patients under age 50. By contrast, 35.4 percent of older patients (greater than or equal to age 50) were women, the study noted. Drop in Lung Cancer Incidence Stopped in Women Kalemkerian's group also learned that the incidence of lung cancer among men during the 15-year study period peaked in 1984, then declined steadily each year until 1999. However, the incidence of the disease in women continued to rise until 1991, then held steady each year until the end of the study period in 1999. "This has resulted in a dramatic narrowing of the male/female incidence …," the authors noted. At its peak in 1984, the rate of lung cancer in men was about 72 cases per 100,000 men per year, then steadily plunged to 47 cases per 100,000 men per year in 1999, the study found. But in women, the rate peaked in 1991 at 33 cases per 100,000 women per year before it plateaued to between 30 and 32 cases per 100,000 women per year between 1991 and 1999. In younger patients, the decrease in the number of cancer diagnoses in men was greater. In patients greater than age 50, however, the rate of lung cancer cases decreased in men, but increased in women, Kalemkerian and his team found, closing the gap even further. Lung Cancer Rates by Therapy Offered The researchers also learned that more women than men who had localized disease had surgery during the 15-year period. For those with minimal metastasis, similar proportions of men and women were initially treated with both surgery and radiation therapy. For those with advanced metastasis, about 50 percent of men versus approximately 47 percent of women were given radiation therapy. Despite the finding that the gap in lung cancer cases between men and women is narrowing, the study also noted that women, overall, had significantly better survival odds at every stage of the disease than men. Overall survival rates did increase, however, in both genders. Reasons Why Lung Cancer Holds Steady in Women The reasons that rates of lung cancer among women are catching up to men isn't precisely known, wrote Kalemkerian and his colleagues. "Although many investigators have suggested that female smokers have an increased susceptibility to the development of lung cancer, prior epidemiologic studies have come to no uniform conclusion on this issue," they wrote. It is possible, though not proven, "that women may have an increased susceptibility to tobacco carcinogens", the study authors added, noting that many more women than men below age 50 had been diagnosed with cancer during the study period. "If the current trends continue, the rates of lung cancer in men and women in the United States will be equal within 10 to 15 years," the researchers predicted. "Despite the good news that the incidence rate for lung cancer in women is no longer rising, the prolonged plateau that has persisted throughout the 1990s without an apparent downward trend is rather disturbing …" 1. Fu JB, Kau TY, Severson RK, Kalemkerian GP. Lung cancer in women: analysis of the national surveillance, epidemiology, and end results database. Chest 2005 Mar;127(3):768-77. 2. Yoshimura A, Kudoh S. Idiopathic pulmonary fibrosis and lung cancer. [Translated from Japanese]. Gan To Kagaku Ryoho 2003 Feb;30(2):215-22. 3. Nagai A, Chiyotani A, Nakadate T, Konno K. Lung cancer in patients with idiopathic pulmonary fibrosis. Tohoku J Exp Med 1992 Jul;167(3):231-7. 4. Pulmonary Fibrosis Foundation. What is Pulmonary Fibrosis? Available at: http://www.pulmonaryfibrosis.org/ipf.htm. Accessed March 17, 2005. 5. Olschewski H, Ghofrani HA, Walmrath D et al. Inhaled prostacyclin and iloprost in severe pulmonary hypertension secondary to lung fibrosis. Am J Respir Crit Care Med 1999 Aug;160(2):600-7. John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.

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