Doctors have known for years that the incidence of deadly liver cancer is on the rise, but what is causing that trend has remained a mystery. Two recent Mayo Clinic studies published in the January issue of Mayo Clinic Proceedings offer a clearer picture of the rise of hepatocellular carcinoma (HCC), or liver cancer, which has tripled in the U.S. in the last three decades and has a 10 to 12 percent five-year survival rate when detected in later stages.
"The studies illuminate the importance of identifying people with risk factors in certain populations to help catch the disease in its early, treatable stages," said W. Ray Kim, M.D., a specialist in Gastroenterology and Hepatology and principal investigator of one study.
Dr. Kim's research group looked at several decades of records in the Rochester Epidemiology Project, a database that accounts for an entire county's inpatient and outpatient care. The study found the overall incidence of HCC in the population (6.9 per 100,000) is higher than has been estimated for the nation based on data from the National Cancer Institute (5.1 per 100,000). The study also found that HCC, which two decades ago tended to be caused by liver-scarring diseases such as cirrhosis from alcohol consumption, is now occurring as a consequence of hepatitis C infection.
"The liver scarring from hepatitis C can take 20 to 30 years to develop into cancer," Dr. Kim says. "We're now seeing cancer patients in their 50s and 60s who contracted hepatitis C 30 years ago and didn't even know they were infected."
Eleven percent of cases were linked to obesity, in particular fatty liver disease.
"It's a small percentage of cases overall," Dr. Kim says. "But with the nationwide obesity epidemic, we believe the rates of liver cancer may dramatically increase in the foreseeable future."
Another study looked exclusively at the Somali population, which is growing in the U.S., particularly in Minnesota, where as many as 50,000 Somalis have settled in the last two decades. The East African country is known to have a high prevalence of hepatitis B, a risk factor for HCC.
Researchers investigating records in the Mayo Clinic Life Sciences System confirmed that hepatitis B remains a risk factor, but they were surprised to find that a significant percentage of liver cancer cases in the population are attributable to hepatitis C, which had not been known to be significantly prevalent.
"The study suggests that screening for hepatitis C would be helpful for the Somali population and would enable close surveillance of liver cancer among those at risk," says lead author Abdirashid Shire, Ph.D., a Mayo Clinic researcher. "That would greatly improve treatment and survival of Somalis with this type of cancer."