In one of the first studies to examine the risk of liver cancer in smokers in the United States, doctors say they've found that the habit may be detrimental to the health of the organ.1
"The effects of smoking on the respiratory system are well known and well documented through research," said Lee Kaplan, MD, PhD, director of the MGH Weight Center at Massachusetts General Hospital in Boston, in a news release about the study. "Recognizing that this high-risk behavior also hurts the digestive system is fundamental in preventing life-threatening cancers and improving overall health."
Is the Risk Similar in the US?
Studies from around the world have examined the association between smoking and hepatocellular carcinoma—the medical term for liver cancer.2-5 But according to Paul Kwo, MD, a gastroenterologist at Indiana University Medical Center, and his colleagues, little research on the risk of liver cancer in smokers have been conducted in North America.
"The impetus for the study was to see if smoking, which appears to raise the risk of hepatocellular carcinoma (HCC) in Asian populations where there is a high prevalence of HBV-related cirrhosis, also raises the risk in a US population where the demographics and risk factors for cancer are different," explained Kwo, the study's senior author, in an interview with Priority Healthcare.
Smoking Risk Compared to Other Factors
To answer the question, Kwo's group collected the records of 272 patients diagnosed with liver cancer at Indiana University Medical Center over an 8-year period. Diagnoses had been confirmed either through biopsy analysis or CT scans. To form a control, or comparison group, Kwo and his colleagues collected the records of 196 patients with chronic liver disease who were not diagnosed with hepatocellular carcinoma during the same period.
The researchers then looked at various potential risk factors for each patient, such as their smoking history, history of alcohol use, diabetes, history of hepatitis and individual demographic information. This information, collected on patients with liver cancer, was compared with patients without cancer.
To further analyze the risk of liver cancer in smokers, the patients were subdivided into two groups: those who smoked less and more often.
Smoking's Apparent Link Found
When all of the risk factors were analyzed, none except smoking more often was associated with a significantly higher risk of developing liver cancer. On average, those who smoked the most faced more than twice the risk of developing the cancer, Kwo and his colleagues found.
One other risk factor that boosted the risk related to race. "African American smokers appeared to have a greater risk of developing HCC than Caucasian smokers," the investigators wrote, though they didn't investigate the reason for that in this study. African Americans smokers faced three times the risk, on average, than Caucasians who smoked, the research found.
"It is not known why the risks are higher in smokers and African-Americans, but could be related to … liver enzymes that metabolize toxins," Kwo said. "African-Americans have a higher risk of HCV infection, which could explain the higher incidence of HCV infection, and we are actively looking at this right now."
A Common Liver Cancer
Hepatocellular carcinoma is considered the most frequent primary tumor of the liver, and ranks as the fifth most common cancer around the world. Cirrhosis is believed to be one of the strongest risk factors associated with liver cancer, with hepatitis B and C one of the main causes of cirrhosis, experts say.6
It's estimated that 17,550 new cases of liver cancer will be diagnosed this year in the United States.7
"As with other organs in the body, the effects of tobacco can have damaging consequences on the liver, significantly increasing the risk of developing liver cancer," said Kwo. "Smoking cessation is one major way that patients can be proactive in preventing liver cancer, especially if they already suffer from chronic liver disease."
1. Kwo PY et al. Cigarette smoking and hepatocellular carcinoma: a case control study in the United States. Digestive Disease Week 2005. 2005 May 14-19. Chicago, IL.
2. Jee SH, Ohrr H, Sull JW, Samet JM. Cigarette smoking, alcohol drinking, hepatitis B, and risk for hepatocellular carcinoma in Korea. J Natl Cancer Inst 2004 Dec 15;96(24):1851-6.
3. Wang LY, You SL, Lu SN et al. Risk of hepatocellular carcinoma and habits of alcohol drinking, betel quid chewing and cigarette smoking: a cohort of 2416 HBsAg-seropositive and 9421 HBsAg-seronegative male residents in Taiwan. Cancer Causes Control 2003 Apr;14(3):241-50.
4. Ogimoto I, Shibata A, Kurozawa Y et al. Risk of death due to hepatocellular carcinoma among smokers and ex-smokers. Univariate analysis of JACC study data. Kurume Med J 2004;51(1):71-81.
5. Mori M, Hara M, Wada I et al. Prospective study of hepatitis B and C viral infections, cigarette smoking, alcohol consumption, and other factors associated with hepatocellular carcinoma risk in Japan. Am J Epidemiol 2000 Jan 15;151(2):131-9.
6. Pons-Renedo F, Llovet JM Hepatocellular carcinoma: a clinical update. Med Gen Med 2003 Jul 22;5(3):11.
7. American Cancer Society. Overview: Liver Cancer. How Many People Get Liver Cancer? Available at: http://www.cancer.org/docroot/CRI/content/CRI_2_2_1X_
How_many_people_get_liver_cancer_25.asp?rnav=cri. Accessed May 26, 2005.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
