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Background: Esophageal squamous cell carcinoma (ESCC) comprises 90% of all esophageal cancer cases globally and is the most common histology in low-resource settings. Eastern Africa has a disproportionately high incidence of ESCC., Methods: We describe the genomic profiles of 61 ESCC cases from Tanzania and compare them to profiles from an existing cohort of ESCC cases from Malawi. We also provide a comparison to ESCC tumors in The Cancer Genome Atlas (TCGA)., Results: We observed substantial transcriptional overlap with other squamous histologies via comparison with TCGA PanCan dataset. DNA analysis revealed known mutational patterns, both genome-wide as well as in genes known to be commonly mutated in ESCC. TP53 mutations were the most common somatic mutation in tumors from both Tanzania and Malawi but were detected at lower frequencies than previously reported in ESCC cases from other settings. In a combined analysis, two unique transcriptional clusters were identified: a proliferative/epithelial cluster and an invasive/migrative/mesenchymal cluster. Mutational signature analysis of the Tanzanian cohort revealed common signatures associated with aging and cytidine deaminase activity (APOBEC) and an absence of signature 29, which was previously reported in the Malawi cohort., Conclusions: This study defines the molecular characteristics of ESCC in Tanzania, and enriches the Eastern African dataset, with findings of overall similarities but also some heterogeneity across two unique sites., Impact: Despite a high burden of ESCC in Eastern Africa, investigations into the genomics in this region are nascent. This represents the largest comprehensive genomic analysis ESCC from sub-Saharan Africa to date., (©2023 American Association for Cancer Research.)

In this issue, Mmbaga and colleagues present results of a case-control study to investigate environmental and lifestyle risk factors for esophageal cancer in Tanzania, East Africa. The results contribute to the early stage of a growing evidence base aimed to inform primary prevention of a major poor prognosis cancer in East Africa. In this commentary, we first discuss considerations needed to evaluate causality of associations, a feature needed for primary prevention. There is a need for further studies across the African esophageal cancer corridor, for more refined exposure assessment and a careful consideration of potential epidemiologic biases within study designs for real-life situations in the setting. This study also forms a prime example of the broader research needs for cancer in low- and middle-income countries and in Sub-Saharan Africa, a setting with distinct and underresearched cancers and exposure patterns. While this etiologic research is challenging, it is an essential component of the ground-shot approach to global health research needed to inform primary prevention. See related article by Mmbaga et al., p. 305 ., (©2021 American Association for Cancer Research.)