Introduction
Liver cancer is the sixth most common neoplasm and the third leading cause of cancer mortality globally in 2020 [
1,
2], with the highest incidence in Eastern Asia. According to the most recent statistics in 2020 of the Hong Kong Cancer Registry (HKCaR) [
3], liver cancer is the fifth most often diagnosed cancer and the third most common cause of cancer deaths in Hong Kong. Over the last three decades, the incidence of liver cancer in Hong Kong has shown a remarkable decline, aligning with the overall trend observed in Eastern Asia [
1,
4].
Hepatocellular carcinoma (HCC) is the predominant histologic type of liver cancer in Hong Kong [
5,
6]. The major causes of HCC are chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), exposure to aflatoxin-contaminated food, excessive alcohol use, obesity, type 2 diabetes, and smoking [
1,
2]. However, the incidence of HCC in Hong Kong may not be related to either HCV infection or aflatoxin contamination, as the prevalence of HCV in Hong Kong is low, at 0.3% [
7], and aflatoxin contamination is rare [
8]. Over the past three decades, the incidence of liver cancer in Hong Kong has declined, mainly due to the decreasing prevalence of HBV in the population [
9‐
11]. Furthermore, as the prevalence of HBV decreases, other risk factors for liver cancer, such as obesity and type 2 diabetes, may become more prevalent and shift the pattern of liver cancer in Hong Kong.
The risk of developing liver cancer varies between birth cohorts due to differences in the prevalence of HBV and HCV infection and other risk factors over time [
1,
2,
9‐
12]. Age-period-cohort (APC) modelling can separate and analyze the effects of temporal changes and birth cohort variation on the incidence of liver cancer [
13,
14]. Knowledge of the incidence trends of liver cancer in Hong Kong can improve disease prevention efforts. In this study, we analyzed the incidence trend of liver cancer in Hong Kong using high-quality population-based cancer registry data. We also examined how age, calendar period, and birth cohort interact and are related to liver cancer incidence in Hong Kong. Furthermore, we projected the future incidence of liver cancer in Hong Kong up to 2030 and decomposed changes in new liver cancer cases into demographic and epidemiological factors.
Discussion
In this study, we employed APC analysis to determine the causes of the incidence trend of liver cancer in Hong Kong. We observed a significant decline in the age-standardized incidence rate of liver cancer in both sexes. Although demographic changes increased the number of liver cancer cases, they were primarily offset by epidemiological changes. We identified a decreasing trend in the period and cohort risk of developing liver cancer for both sexes. Our research findings demonstrated that demographic factors account for the majority of new liver cancer cases in Hong Kong, and the diminishing cohort effects suggest a transition in the risk factors for liver cancer in the population. Continued epidemiological surveillance and preventative approaches are essential for addressing this disease.
The declining trend in the period and cohort risk of developing liver cancer in Hong Kong is encouraging. It suggests that the efforts to prevent and control hepatitis B have been effective. In Hong Kong, the seroprevalence of hepatitis B surface antigen (HBsAg) has declined in several populations with no obvious HBV risk, such as new blood donors and pregnant women [
24]. Hong Kong has transitioned from a high-intermediate to an intermediate-low hepatitis B endemicity over the last few decades. In addition, antiviral treatment for hepatitis B carriers in the late 1990s has led to a sustained decline in the period risk of developing liver cancer [
25,
26]. According to a series of vaccination coverage surveys [
27], the coverage of the third dose of the hepatitis B vaccine has consistently been around 99% or higher among children aged 3–5, implying that the cohort risk of developing liver cancer will continue to wane for birth cohort after 1988. Adults in their 30s who did not receive protection from the universal neonatal hepatitis B vaccination program, which began in 1988, bear the burden of HBV infection. Recent research indicated that the overall HBsAg seroprevalence is as high as 7.2% [
7], implying that over 500,000 people have chronic hepatitis B in Hong Kong. To further reduce the burden of liver cancer in Hong Kong, it is essential to improve prevention measures against mother-to-child transmission and provide access to appropriate medical management for those who have chronic hepatitis B.
Another significant contribution of this study is predicting the trend of liver cancer incidence in Hong Kong. Our analysis indicates a significant downward trend in the age-standardized incidence of liver cancer, but the number of cases remains high. The inconsistency is mainly due to demographic changes in Hong Kong, namely, ageing. In addition to viral infections, other factors such as excessive alcohol consumption, overweight, type 2 diabetes, and smoking may increase, particularly in males [
23,
28]. Demographic changes, such as population ageing and growth, may exacerbate the role of these risk factors in liver cancer development. In individuals without hepatitis virus infection, the abovementioned risk plays a more significant role in developing liver cancer. According to the Hong Kong Department of Health [
27], 8.8% of people aged 15 and above drink alcohol regularly, with the highest rate of 12% observed among those aged 55–64. Additionally, 29.9% of the population is obese, and 20.1% are overweight. The prevalence of diabetes is 8.4%, and the prevalence of smoking remains above 10.5%. As the population ages, the increasing incidence of diabetes and obesity [
23,
28] will continue to contribute to the development of liver cancer, and the proportion of liver cancers caused by metabolic disorders will increase. However, it should be noted that our dataset lacks specific data on risk factors.
In Hong Kong, liver cancer incidence is significantly higher in males than females, with females experiencing less than one-third of the incidence observed in males due to differences in risk factors. While the contribution of epidemiological factors remained stable for females after 2020, demographic factors, particularly population aging, continued to influence liver cancer incidence. Unlike males, where demographic and epidemiological factors combined to decrease incidence, the stable contribution of epidemiological factors in females could not offset the impact of demographics. This may result in a potential increase in the absolute number of liver cancer cases in females, albeit at a lower level compared to males. Despite this, the incidence rate and number of liver cancer cases in females in Hong Kong remain significantly lower than in males, underscoring the need for gender-specific risk factor considerations in liver cancer prevention and control strategies.
This study possesses several notable strengths that contribute to understanding liver cancer incidence in Hong Kong. Firstly, it is the most extensive epidemiological study on age-period-cohort associations with liver cancer, analyzing nearly all liver cancer cases in the region over 30 years. This extensive dataset provides robust and reliable estimates of the period and cohort effects on liver cancer incidence. Moreover, the study offers valuable insights into the future incidence of liver cancer in Hong Kong. By projecting the trends observed in the data, the study provides essential information for public health planning and resource allocation.
However, our study also has some limitations. First, liver cancer can be classified into two subtypes: HCC and intrahepatic cholangiocarcinomas, each with distinct risk factors, carcinogenesis, and epidemiological patterns. However, the HKCaR does not differentiate between these subtypes, which limits our ability to analyze and interpret the data accurately. Second, the HKCaR lacks essential individual-level information, such as hepatitis virus infection status, alcohol consumption, obesity, diabetes, or smoking history. This lack of data on crucial risk factors hampers our ability to comprehensively examine the population’s underlying causes of liver cancer. Third, the population structure and size of Hong Kong were derived from the UN World Population Prospects, which may contain significant biases. These biases could affect the accuracy of our findings and projections. Finally, using different modelling approaches introduces variations that could impact the accuracy of our predictions. Care should be taken in interpreting the results and considering the potential uncertainties associated with the modelling techniques employed. Future research should address our study’s limitations by incorporating subtype-specific data, including individual-level risk factor information, and refining population data.
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