War-Related Factors and Conditional Scenario Estimates of Registered Cancer Deaths in Gaza: A Systematic Review, Meta-Analysis, and Monte Carlo Simulation Study

Abstract Objective To identify war-related factors affecting patients with cancer, synthesize their associations with cancer-specific mortality, and estimate changes in registered cancer deaths under multifactor scenarios in Gaza during October–December 2023. Methods PubMed, Web of Science, Embase, and Cochrane Library were searched. Two reviewers independently screened studies, extracted factors, and identified a cancer-patient subset. Cancer-specific mortality or survival effects were pooled for six factor groups using REML random-effects models. Gaza registered cancer deaths and population data from 2016–2022 were used to estimate a 2023 counterfactual registry baseline with a Pearson-dispersion-corrected Poisson model and 100,000 Monte Carlo simulations. Five non-environmental factors were combined with treatment delay or interruption in a primary six-factor joint model. Particulate-matter exposure was included only in exploratory analyses. Results The review identified 1,341 factor records from 413 studies and 263 standardized factors. The cancer subset contained 23 studies, 67 records, and 29 standardized factors. Twenty-eight studies contributed 29 poolable estimates. Diagnostic delay (HR 1.401, 95% CI 1.077–1.822) and psychosocial stress (HR 1.237, 1.019–1.501) were positively associated with cancer-specific mortality. The particulate-matter estimate was highly heterogeneous (HR 1.427, 1.075–1.894; I²=98.7%). The counterfactual baseline was 997.2 registered deaths (95% UI 834.4–1189.3). Under the no-attenuation upper-bound assumption of g = 1.00, the primary six-factor model estimated 173.5 additional registered deaths (90.9–286.5). Across g = 0.35–1.00, the increment ranged from 60.7 to 173.5 deaths. A flat-rate baseline sensitivity produced 127.8 additional deaths (65.5–215.0). Exploratory addition of particulate-matter exposure increased the estimate to 239.8 deaths (131.2–391.6). Conclusion War-related cancer factors were concentrated in health services and systems. Diagnostic delay and psychosocial stress showed positive pooled associations, while particulate matter remained exploratory. The estimated increments are conditional scenarios rather than observed or directly war-attributable deaths and depend on assumptions about baseline trends, exposure mapping, effect transport, overlap, and pathway coverage.