Study design
We conducted a case-only prospective cohort study nested in Polycyclic Aromatic hydrocarbon exposures and Dietary Risk of Esophageal squamous cell carcinoma in southwestern Uganda (PADRE) study a case-control study that enrolled participants between January 2018 and March 2020 in the endoscopy unit of Mbarara Regional Referral Hospital (MRRH), southwestern Uganda previously described.[10]. Briefly, patients with gastrointestinal symptoms are referred from within MRRH and southwestern Uganda for esophagogastroscopy at MRRH. In this setting, patients for upper gastrointestinal endoscopy often present with advanced ESCC disease (stage III or stage IV). For this study, participants were patients who were diagnosed with ESCC at esophagogastroscopy and tissue histology. To be eligible for the study, ESCC cases had to be 18 years or greater, never have been diagnosed or treated for ESCC. Patients with no features of esophageal masses on EGD and histology findings other than ESCC were excluded.
After written informed consent, esophagogastroscopy was performed to characterize abnormalities in the esophagus and collect esophageal tissue for histology. During diagnostic upper gastrointestinal endoscopy, we collected information about any suspicious esophageal lesions, describing the location i.e., upper third (15–24 cm), middle third (24–32 cm), and lower third (32–40 cm), traversibility (accessing if one could pass the scope beyond the lesion – indicating if the lesion was obstructive in nature), and collecting 3 esophageal biopsies for histology.[10] At the MUST histopathology laboratory, esophageal biopsies were processed and stained with Hematoxylin and eosin.
Slides containing the stained histopathological specimens were then examined using standard diagnostic criteria for microscopic atypia for esophageal squamous cell carcinoma, pathologist reported features such as presence of nuclear atypia, prominent keratinization and evidence of invasion. [11]
Interviews were conducted at the endoscopy unit of Mbarara Regional Referral Hospital (MRRH) to obtain socio-demographic information including age, gender, and socioeconomic status based on ownership of household items. We also extracted clinical data from clinical records including family history of diagnosed gastrointestinal cancer, symptoms at presentation to MRRH and associated durations.
Of note, participants had the discretion to accept/decline chemotherapy and cancer management was at the discretion of the Oncology physicians. The chemotherapeutic regimen used for ESCC at MRRH is Cisplatin and 5-fluorouracil (5-FU). This is provided free of charge when available otherwise if not available patients’ pay out of pocket from private pharmacies. Radiotherapy is only administered at Uganda Cancer Institute (UCI), Kampala.
Each participant was requested to provide a list of at least 3 of their telephone contacts, those of a relative living with participant or neighbor to enable locating the participant. Participants were actively followed every month post-hospital discharge until death.
Data analysis
We used principal component analysis to generate an assets index score based on household utilities and assets to derive composite measures of socioeconomic status with highest discriminatory capabilities. Participants were divided into tertiles (low, fair, and high socioeconomic status).
Participant demographic and clinical characteristics were summarized for the entire group: means (sd) for continuous variables and counts (percentages) for categorical variables. The follow-up time was the time interval from EGD test to death. Participants who were alive at their last follow-up were censored at the last follow-up date (December 1, 2020).
The primary outcome was overall survival over one year of follow-up. Kaplan-Meier analysis was used for estimating survival probabilities for the overall sample, gender, and socioeconomic status.
Multivariable Cox proportional hazards regression analysis was performed to identify potential factors associated with hazard of death. We adjusted for Age, gender, socioeconomic status, and family history of upper gastrointestinal cancer (Buccal cavity, esophagus, and stomach) (model 1). In model 2, we further adjusted model 1 for measures of disease severity such as untraversability of esophageal lesion during EGD (obstruction), anemia (hemoglobin <7mg/dL), histological features (cell differentiation and invasion of the stromal layer) and in model 3 we adjusted model 2 for receipt of chemoradiotherapy to control the possibility of confounding by indication. We conducted these analyses in a sample with all available data and those with complete data on all covariates.
For comparability of mortality rates across regions and time, we calculated age-standardized mortality rates (SMRs) separately for men and women within the age groups (30 to 45, 45 to 54, 55 to 64, 65 to 74, and 75 or greater) using direct standardization to the World Health Organization Standard Population age-structure for the period 2000-2025.[12] The overall rates by strata indicate the rate that would result if all populations had the same age distribution.[13]
All analyses were performed using Stata version 15.1 (Stata Corp., TX, USA). We determined statistical significance by a 2-sided p-value of less than 0.05.