Why Temporal Association Isn't Causation

BUFFALO, NY – January 8, 2026 – A new #review was #published in Oncotarget (Volume 17) on January 3, 2026, titled “COVID vaccination and post-infection cancer signals: Evaluating patterns and potential biological mechanisms.” Led by Charlotte Kuperwasser from Tufts University School of Medicine and Oncotarget Editor-in-Chief Wafik S. El-Deiry from The Warren Alpert Medical School of Brown University, the review examines published reports describing cancers that appeared after COVID-19 vaccination or SARS-CoV-2 infection. The authors analyze patterns across case reports, small patient series, and large population studies, and explain why these observations are relevant for cancer research and long-term public health monitoring. Cancer remains a major global health concern, and understanding factors that may influence its behavior is important. The review covers reports published between January 2020 and October 2025 that describe cancer diagnoses, recurrence, or unusually rapid disease progression following vaccination or infection. In total, 69 publications were reviewed. Sixty-six article reports, representing more than 300 patients across multiple countries and cancer types; 2 retrospective investigations; and one longitudinal study spanning the pre-pandemic through post-pandemic periods. The review explores how immune responses triggered by infection or vaccination could, in some individuals, influence existing cancer cells or previously dormant disease. Many article reports involved blood cancers such as lymphomas and leukemias and solid tumors, including breast, lung, pancreatic, brain, and skin cancers. Some cases described rapid disease progression or cancers appearing near vaccine injection sites or nearby lymph nodes. These observations are described as hypothesis-generating rather than evidence of risk. In addition to individual case reports, the review examines findings from large population studies in South Korea, Italy, and the United States military. These studies assessed cancer trends over time in vaccinated populations and reported modest associations for certain cancer types. The authors note that these findings are limited by short follow-up periods and potential reporting and detection biases, emphasizing the need for longer-term data. The authors also discuss possible biological explanations for the reported patterns, including temporary immune changes, inflammation, or altered immune surveillance that could affect tumor behavior in people with undetected or controlled cancer. They place these observations within the broader context of how viral infections can interact with cancer biology. “Establishing causality between SARS-CoV-2 infection, COVID-19 vaccination, and cancer requires a level of evidence far beyond temporal association.” Overall, the review identifies significant gaps in current knowledge about possible associations between COVID-19 vaccination and cancer, including limited long-term cancer surveillance, lack of molecular data, and an incomplete understanding of individual susceptibility. The authors emphasize the need for carefully designed studies that integrate clinical, epidemiologic, and biological evidence. Finally, they conclude that examining these reported patterns is important for advancing cancer research and supporting informed public health discussions. DOI - https://doi.org/10.18632/oncotarget.28824 Correspondence to - Charlotte Kuperwasser - charlotte.kuperwasser@tufts.edu, and Wafik S. El-Deiry - wafik@brown.edu Abstract video - https://www.youtube.com/watch?v=5_-AaojOoR8 To learn more about Oncotarget, please visit https://www.oncotarget.com. MEDIA@IMPACTJOURNALS.COM