We found an upward trend of the CRC incidence with a higher rate increasing in men than women in Ho Chi Minh City, consistent with the patterns in other Asian countries over recent decades. However, our result differed from these countries - an appreciably higher rising occurred in the older than younger individuals. Regarding topography, the rectum accounted for the most prevalent anatomical subsite and had the highest rising rate in both genders. Furthermore, the APC analysis indicated significant period and cohort effects among both men and women, in which people born from the 1976-1980 period increased the CRC risk strikingly.
Many decades ago, CRC was rare in developing and low-risk areas such as Asia and was most common in high Human Development Index countries. In recent years, many studies reported the rapid increase of CRC incidence in Asia nations3–5. Till 2015, the ASR of CRC in South Korea, Singapore, Japan, Taiwan, and Hong Kong was 45, 33.7, 32.2, 45.3, and 38.4, respectively.
For the underlying reasons of the elevating trend in Ho Chi Minh City, the strong period and cohort effects among either gender in the recent timeframe suggest the increase in the prevalence of exposure to risk factors and improvements in diagnostic technique and healthcare access. As similar to other Asian countries, the rising prevalence of westernized lifestyles is likely the most important etiology of increasing CRC incidence in Ho Chi Minh City6,7. The westernization of lifestyle, including unhealthy diet, physical inactivity, obesity, alcohol consumption, and smoking, were demonstrated to considerably increase CRC risk19. For recent decades, Ho Chi Minh City has been Vietnam’s fastest-growing major economic city. This economic transition and urbanization are associated with the westernized lifestyle adoption. The prevalence of overweight and obesity among adolescents in Ho Chi Minh City increased sharply from 5.8% to 13.7% during 2002-200420. In 2005, a cross-sectional study on 25-64 years old people in Ho Chi Minh City found that most adults were physically inactive, and only 56.2% of them achieving the minimum recommendation of “doing 30 minutes moderate-intensity physical activity for at least five days per week”21. In Vietnam, the overall alcohol consumption rose strikingly during 2010-2015, and the overall tobacco smoking prevalence has been slowly decreasing but was still high22. In addition, another potential etiology is the long-term antibiotic use in early to middle adulthood, which increases the risk colorectal adenoma risk23. Vietnam was reported to have a high prevalence of overuse and inappropriate use of antibiotics in hospitals and the community24. Parallel with the socioeconomic growth in Ho Chi Minh City, there have been improvements in healthcare accessibility, and more advanced diagnostic techniques introduced (colonoscopy, computed tomography, magnetic resonance imaging, ultrasound, fecal occult blood test, and fecal immunochemical test), which enhanced the detecting rate of CRC.
In accordance with previous data from most parts of the world, our study found that CRC rates were higher in men than in women1. The APC analysis revealed that men and women had the CRC rates elevate along with aging, in which the risk was much higher in men than women from the age of 60-64 years old. This discrepancy might result from the higher prevalence of risk behaviors (smoking and alcohol uptake) in men and the protective effect of endogenous estrogens against CRC tumorigenesis in postmenopausal women25.
In contrast to many other Asian nations, Ho Chi Minh City experienced a marked increasing CRC incidence trend in the old population than in the younger counterparts. A modest but significant escalating of early-onset CRC was reported in Taiwan, Korea, Japan, and Hong Kong from 1995 to 201426. This difference could result from the screening programs mature and improvement in other Asian countries while the organised CRC screening has not been implemented in Vietnam until now. Several Asian countries implemented the population-based CRC screening program in recent decades, such as Japan (since 1992), Korea (since 2004), China (since the 2000s), Taiwan (since 2004), Hong Kong (since 2017), Thailand (since 2011), and Singapore (since 2011)27–29. The starting age screening age for average-risk individuals in those programs ranged from 40 to 50 years old. Since all CRC cases in Ho Chi Minh City were opportunistic diagnosed, Ho Chi Minh City's CRC incidence might undervalue the true rate of early-onset diagnoses. Together with the overall increase of CRC incidence, particularly in people born from the 1976-1980 period, Ho Chi Minh City might be in need of launching a population-based CRC screening program to early diagnose the CRC and improve the overall disease outcome.
Regarding anatomical subsite, our study found that rectal cancer had the highest rate rising while the proximal and distal colon increased relatively in both genders. Globally, the CRC subsites trend varied widely. There has been a proximal shift in the CRC subsite distribution in various countries globally, such as the USA (1970-2000), Canada (1964-2004), Japan (1974-1994), Norway (1962-2006), and Luxembourg (1988-1998)12,30–33. Conversely, this trend has not been observed in several other countries, such as Italy (1984-1998), Iran (1994-2009), and Korea (1999-2009), as the rate increased in all CRC subsites or right-sided cancer did not increase statistically significant34–36. The reasons for these conflicting findings remain unclear but might be explained by the complex attributions of risk factors on different tumor segments. A study from Japan demonstrated that heavy tobacco smoking was linked with increased rectal cancer risk in men but not women37. This study also indicated that high alcohol consumption was substantially associated with rectal cancer risk in women while increased the risk of colon cancer in either gender insignificantly. Another study on Japanese men reported that alcohol intake was associated with a statistically significant increased risk of distal and rectal cancer, but not proximal cancer38. Regarding body mass index, overweight and obesity were reported to elevate colon cancer risk in men but not women37,39. Meanwhile, a Korean study reported that a high body mass index was associated with increased risk for proximal colon cancer among women, and a study on Asian women outlined that obesity is positively associated with colon cancer but not rectal cancer40,41. Physical inactivity had shown a strong association with the risk of proximal colon cancer in women but not with rectal cancer in both genders42. We need further studies to ascertain whether there is a true proximal shift trend of CRC in Vietnam and find associated factors. This is essential in choosing the preferred screening test modality between sigmoidoscopy and total colonoscopy.
The Ho Chi Minh Cancer Registry collected CRC archives from all hospitals in Ho Chi Minh City for a longterm. Its coverage could be representative of CRC epidemiology on a regional scale. However, the present study had some limitations. Associated factor data were not available or lack of completeness, such as family history, heredity cancer syndromes, socio-economic characteristics, the basis of diagnosis test frequency, and cancer staging. The high proportion of the other CRC subsites (26.8%) might affect the topography analysis accuracy. Many other Asian nations also reported high proportions of overlapping and unspecified lesions of CRC43. Additionally, due to the confounding and mixture among age, period, and cohort effects, the interpretations of results should be used with cautions of misleading, particularly at the individual level.