The impact of single and multiple occurrences, as well as the sequence of occurrences, of primary gastrointestinal cancer on overall survival: a comprehensive analysis based on the surveillance, epidemiology, and end results database in the United States from 2016 to 2019.

Introduction: Gastrointestinal cancers encompass malignant tumors of multiple digestive system organs in humans. Each type of digestive system cancer also contains different histological types, each of which has a distinct prognosis. The survival time of cancer patients has significantly extended with the development of modern medicine, allowing for primary cancers occurring more than once in a lifetime.

Methods: The study analyzed multiple primary gastrointestinal cancers, including esophagus, stomach, liver, gallbladder, small bowel, colon, rectum, and anus, based on the Surveillance, Epidemiology, and End Results (SEER) database from 2016 to 2019 in the United States. A total of 119,760 cases were included in this study. Each gastrointestinal cancer was analyzed separately based on the International Classification of Diseases for Oncology third edition (ICD-O-3) for the common histologic type. Meanwhile, based on the sequence of cancer occurrence in the patients, they were divided into the one primary (OP) group and the multiple primaries (MP) group. The multiple primaries group was further subdivided into the first of multiple primaries (FMP) group and the non-first of multiple primaries (NFMP) group. The Kaplan-Meier method with the log-rank test was used to analyze overall survival (OS), while the Cox regression model was used for univariate and multivariate analyses.

Results: The study enrolled nine organs of the digestive system and twenty histologic types of primary gastrointestinal cancers. The characteristics of patients in different groups with various cancers, overall survival of these patients, and the risk factors for developing these cancers were comprehensively analyzed. The comprehensive analysis revealed the connection between the occurrence sequence of cancers and different outcomes for patients.

Conclusions: Different prognoses were observed in patients with different sequences of various primary gastrointestinal cancers. Patients with high mortality cancers in the FMP group may have potential factors, such as high treatment sensitivity, that could lead to improved OS. Patients with low mortality cancers in the NFMP group could benefit from positive treatment therapies.