In an interview with <em>Targeted Oncology</em>, Katherine A. McGlynn, PhD, MPH, discussed the population attributable fraction of non-alcoholic fatty liver disease in developing hepatocellular carcinoma, as well as related disorders, in the United States that contribute to the risk of mortality.<br />
Katherine A. McGlynn, PhD, MPH
Although the rate of hepatocellular carcinoma (HCC) has been on the decline since 2012 in the United States, patients with non-alcoholic fatty liver disease (NAFLD) have an increased risk of mortality and of developing HCC, according to a presentation at the 2019 International Liver Cancer Association Annual Conference.
In a recent analysis, investigators looked at data from patients who underwent an abdominal ultrasound in the Third National Health and Nutrition Examination Survey (NHANES III) study between 1988 and 1994. This allowed for 21 to 27 years of follow-up of mortality after the initial ultrasound.
NAFLD was seen in 33% of the patients examined in this analysis, where 35% were males and 31% were females. Additionally, NAFLD was seen more commonly in Mexican Americans, around 40%, compared with 32% in Caucasians and 29% in African Americans. Age also appeared to play a role in the development of NAFLD, where about 40% of patients over the age of 50 had NAFLD compared with 20% in younger patients.
About one-third of deaths in patients were caused by cardiovascular disease, with cancernotably HCC—as the second leading cause. Other risk factors that played a role in mortality among these patients included excessive alcohol consumption, smoking, and obesity.
In an interview withTargeted Oncology, Katherine A. McGlynn, PhD, MPH, senior investigator in the Division of Cancer Epidemiology and Genetics at the National Cancer Institute, discussed the population attributable fraction of NAFLD in developing HCC, as well as related disorders, in the United States that contribute to the risk of mortality.
TARGETED ONCOLOGY:Could you share an overview of your session at the 2019 ILCA Annual Conference?
McGlynn:We opened with talking about rates of HCC around the world and in the United States. It looks like rates in the United States may have plateaued and started to decline, which is very good news. However, several years ago when we started studying why rates were going up, we calculated population attributable fractions, which we did for all of the risk factors that we could [measure] using data from the SEER Medicare Program. The cancer diagnosis comes from SEER, the data come from Medicare, and this gives you a good idea of what the contribution of risk factors make.
We calculated odds ratios. Using odds ratio and prevalence of the population, we calculated population attributable risks for the risk factors. We found that although hepatitis C virus (HCV) and hepatitis B virus (HBV) have, by far, the biggest odds ratios [for developing HCC], and are the biggest risk to the individual themselves, on a population basis, the metabolic disorders and NAFLD make a much bigger contribution because they are much more common in the population.
We also looked at the contribution of NAFLD to overall mortality in the population because if you’re just concentrating on HCC, that is a fairly rare outcome, but in terms of total population mortality, we use data from the NHANES III population to look at risk of mortality among people who had NAFLD and people who did not. We found that there is a significantly increased risk of mortality in people who have NAFLD, and there was a significantly increased risk of diabetes mortality. Among men, there was also a significantly increased risk in liver disease mortality. I think those are very important findings and will need to be followed because unfortunately, the risk of NAFLD is increasing in the population with the risk of obesity.
TARGETED ONCOLOGY:What do you think is contributing to this decline in HCC in the United States?
McGlynn:We are not entirely sure, but it could be that HCV as a risk factor is maybe diminishing now, although the rate of decline started around 2012. That was before any of the direct-acting antivirals were able to have a big effect in the population. We are not entirely sure what’s going on because the percentage of the population that was supposed to have the big HCV effect were the Baby Boomers born between 1945 and 1965. The projections on the [Baby Boomers] we were going to see in HCC were based on them having a big risk of HCC overtime. However, the decline started happening when the average Baby Boomer was 57 years old, which is before the age of HCC. In the population, the mean age of HCC in men is about 62 and in women, it’s about 68. Having this peak out when Baby Boomers were 57 was a little unexpected, but it could be that [those with] HCV are just doing better. There’s probably very little effect in treating HBV because HBV is a much less significant risk factor in the population, so we are not quite sure what’s going on yet.
TARGETED ONCOLOGY:What risk factors did you look at?
McGlynn:The ones that we looked at were [those with] HCV, obviously, which was long thought to be a driving risk in the United States. We looked at HBV, excessive alcohol consumption, smoking to some extent, rare genetic disorders, and the metabolic disorders. We found that, obviously, the biggest increased risk to the person was HCV. There was about a 50-fold increased risk if you have an HCV infection of developing HCC. With HBV, the risk was about 18-fold or higher. The genetic disorders and alcohol consumption were about a 7-fold increased risk. The metabolic disorders, comparatively, were about a 3-fold increased risk, so you think by looking at that, metabolic disorders aren’t contributing much, but you have to keep in mind that when you calculate odds ratios, you’re talking about the risk in a person who has that risk factor. It’s not a population perspective, really. It’s just if you have a particular risk factor.
What we did then to calculate the population’s attributable risk is you take into account both the odds of developing HCC and the prevalence in the population to calculate the risk factor. Once you do that, metabolic disorders rise to the top; about 35% of tumors were related to the metabolic disorders, including NAFLD-impaired, fasting-glucose, metabolic syndrome. We also got medical codes for obesity and diabetes in there. It was basically any of this whole group of disorders that are very highly correlated, so 35% of tumors in the population related to those [disorders] is fairly impressive.
HCV was second in about 20% of tumors, and then, as you went down, there were fewer and fewer percentages of tumors related. HBV was only about 4%, for example. Of course, they differed by sex, race, and ethnicity. HCV had a much bigger effect in blacks. The metabolic disorders have a bigger effect in whites and Hispanics. It’s always good to keep in mind that we are a multi-racial, multi-ethnic population, so you have to account for differences. Also, there were differences by sex.
TARGETED ONCOLOGY:Could you discuss the risk of mortality in these patients?
McGlynn:This, as I mentioned, was done in the NHANES III study. The NHANES III study is a cross-sectional study of the population that is going on in the United States somewhere all the time. We use data from the [portion of the] NHANES III, however, which took place between 1988 and 1994. We wanted to use that particular version of it because abdominal ultrasound was done for the adults during that part of the study, and you get a much better feel for NAFLD using abdominal ultrasound than you do using any of these indices, which rely on the combination of things like liver enzymes and so on and so forth.
The other thing we wanted to use NHANES III for was that there was sufficient time for mortality events to occur. If you figure people were enrolled between 1988 and 1994, it had been about 21 to 27 years of follow-up. Some of the other analyses that had been done were done after like 10 years of follow-up, which is insufficient time for deaths [to occur].
In the population, what we found was that about 35% of the population had NAFLD, which is a little bit higher than you’ve heard from some other [data] are coming out. It was based on ultrasound, so I think this is accurate. It was more common among males, about 35% of males and 31% of females have NAFLD. Overall it was more like 32% to 33%. It was higher in Mexican Americans, which has been widely reported previously, at about 40%. About 32% of whites and again, it’s been reported in a lower percentage among blacks, around 29%. It was higher with age. By the time you got to 50 and over, about 40% of the population had NAFLD versus 20% in younger patients.
We took those outcomes and we looked at the deaths and causes of death. About a third, around 1500 deaths, occurred among the individuals with NAFLD. Over a third of those were due to cardiovascular disease; again, that was not a surprise because it was previously reported, cancers were next, and then we had deaths from liver disease, kidney disease, and diabetes. Of these, the ones that were significantly higher among individuals with NAFLD were all-cause mortality with about a 20% increased risk in diabetes mortality, which was about a 2-and-a-quarter-fold increased risk of death.
If you then calculate the population of attributable fraction, it turns out that about 7.5% of people who die in the United States, at least in 2015, had a NAFLD-related mortality. That doesn’t sound huge; it’s about 200,000 deaths out of about 2.7 million deaths that year. However, if you look at some other risk factors, it puts it into perceptive because smoking accounts for anywhere between 18% and 25% of deaths. Obesity is probably around 18%, and that is, of course, a co-traveler with NAFLD. Alcohol is lower, at around 2% to 6%. Smoking is going down in the population, so in terms of being a major risk factor contributing to death, smoking, hopefully, will become less and less of a factor. Unfortunately, obesity and as a result NAFLD, are increasing, so the latest data from NHANES III show that we had thought the obesity epidemic had leveled off in the United States, but according to these data, it has unfortunately not. It’s gone up again, so it is a contributing cause of death. I think it’s a real problem, and 1 that needs to be taken seriously.
TARGETED ONCOLOGY:Is there anything in particular you’d like to highlight from this analysis?
McGlynn:We were surprised to see that the rates may be going down, but they may again level off because HCV can run a much higher risk to the person, so if you have had HCV, your likelihood of developing HCC was great. That may have contributed to this big rise. Maybe what we are seeing is just a leveling off, and we will see it plateauing with NAFLD because NAFLD does not, by any chance, have the same effect that HCV does. However, we all recognize with NAFLD that the biggest risk is not in developing HCC; it’s in developing cardiovascular disease. Cardiovascular disease rates have been going down in the United States for many years, so hopefully this is not going to bring them back up again.