Background Multimorbidity, defined as the coexistence of two or more chronic diseases, is increasingly common among cancer patients and is associated with higher risks of hospitalization, complications, and mortality, posing large challenges to clinical practice and health systems. Gastrointestinal (GI) cancers account for approximately one-third of cancer-related deaths worldwide. Previous studies have mainly examined the impact of multimorbidity on cancer risk factors, screening, and treatment, with most evidence coming from high-income countries in Europe and North America, and limited evidence from low- and middle-income countries. 

Objectives To analyze the incidence of GI cancer and the prevalence of multimorbidity among GI cancer patients in 2020 using a regional health information platform in China, and to examine its distribution by age, sex, ethnicity, and socioeconomic status. 

Methods This cross-sectional study used data from the Inner Mongolia regional health information platform, comprising cancer registry, medical insurance, and cause-of-death reporting system data. GI cancer patients, including esophageal, gastric, colorectal, liver, gallbladder, and pancreatic cancer, were identified using International Classification of Diseases, Tenth Revision codes. Crude incidence rates per 100,000 were calculated for each cancer type and further standardized using the Chinese population in 2000 and the 1966 Segi-Doll World standard population. Multimorbidity was defined as having at least one of eight predefined chronic conditions identified in previous studies in addition to cancer. The proportion of each condition and the prevalence of multimorbidity were calculated. Sociodemographic variables included age (5-year age group, 0-85+), sex (male or female), and ethnic group (Han or Mongolian). Socioeconomic status was measured by education level, occupation, and marital status. Analyses were conducted using R version 4.5.1. 

Results A total of 2,476, 4,954, 7,292, 4,643, 320, and 1,967 patients were identified with esophageal, gastric, colorectal, liver, gallbladder, and pancreatic cancer in 2020, respectively. The age-standardized incidence rates (ASIR) under the Chinese standard population were 6.84, 14.22, 21.39, 13.46, 0.87, and 5.51 per 100,000, respectively, with similar results under the World standard population. The incidence and all GI cancers increased rapidly after age 40. Except for gallbladder cancer, all other GI cancers had higher incidence rates in males than females, with the male-to-female ASIR ratios ranging from 1.49 to 9.09. Ethnic-specific incidence rates showed similar patterns, with the Mongolian-to-Han ASIR ratios ranging from 1.28 to 4.02, except for gallbladder cancer. Based on the literature, the eight predefined chronic conditions/diseases include diabetes, coronary heart disease, stroke, chronic obstructive pulmonary disease, depression, arthritis, dementia, and Parkinson's disease. The distribution and prevalence of multimorbidity among GI cancer patients are under analysis. 

Implications As the third largest province in China, Inner Mongolia has over four million people of Mongolian ethnicity, representing over 70% of the Mongolian population in China and about half worldwide, providing a valuable population base for studying cancer burden among ethnic minority groups. The current findings indicate a higher burden of GI cancer among males and Mongolians. Given the importance of multimorbidity in cancer management and outcomes, further investigation across sociodemographic and socioeconomic groups is warranted to inform targeted prevention.