South Korea’s gastric cancer screening (GC) program has reduced disease-related mortality by 41%.
Japan’s? Not at all.
These findings suggest that the benefits of nationwide gastric cancer screening may vary widely between countries while offering insights into program best practices, reported lead author Dianqin Sun, a PhD candidate at the University Medical Center, Rotterdam, the Netherlands, and colleagues.
Mr. Sun
Dianqin Sun
“Despite the lack of evidence from randomized controlled trials, South Korea and Japan, two countries with a high GC incidence, have been at the forefront of GC secondary prevention and have implemented nationwide organized GC screening programs for decades using endoscopy or upper gastrointestinal series,” the investigators wrote in Gastroenterology.
Although individual-level data from both programs supports their efficacy in reducing GC-related death, the investigators noted that these studies have been limited by volunteer bias, and population-level data remain scarce.
To address this knowledge gap, Mr. Sun and colleagues used the flexible synthetic control method to determine how screening programs affected GC mortality rate, as well as a composite mortality rate for esophageal cancer and peptic ulcer.
“The concept of the synthetic control method is to construct a synthetic control for the treated country by deriving a weighted average of multiple control countries without intervention,” the investigators wrote. “The weight of controls is determined in a data-driven way to minimize the differences in preintervention outcomes (i.e., GC mortality before the introduction of nationwide screening) and other covariates associated with GC mortality between the treated country and the synthetic control.”
This approach revealed starkly different benefits for South Korea and Japan.
Compared with the synthetic control, South Korea’s screening program was associated with a 17% reduction in GC mortality risk on average, with risk dropping as far as 41% after the 15th year of screening. The Korean program was also associated with a 28% reduction in mortality from esophageal cancer and peptic ulcer, with this rate decreasing as much as 53% after 15 years of screening.
In sharp contrast, Japan’s mortality rates for GC and the other GI diseases were not significantly different from the synthetic control after 34 years of screening.
The investigators suggested several possible factors behind the lack of benefit in Japan, including the absence of a recommendation for endoscopic screening until 2014. In 2015, just 19% of municipalities in Japan were using endoscopy for screening, compared with more than 72% in South Korea in 2011. Furthermore, guideline adherence and screening program adherence are lower in Japan, they noted.
“Therefore, the findings in our study may have been expected,” the investigators wrote. “However, it is important to note that certain covariates were unavailable for the analysis in Japan, which may have introduced potential biases, the directions of which are unclear. Further studies are needed to compare the screening impact in South Korea and Japan.”
Meanwhile, the present results could guide screening programs around the world, Mr. Sun and colleagues suggested.
“This [study] highlights the significance of a well-planned organizational structure and evidence-based decision making when organized screening is started,” they wrote. “With a quasi-experimental design, this study will facilitate triangulating current observational evidence and provide valuable insights while the GC screening randomized controlled trials are still underway. The data and experience from South Korea and Japan will inform GC screening policy in other countries.”
The investigators disclosed no conflicts of interest.
