A systematic review of 69 peer-reviewed publications on COVID-19 and cancer identified a potential safety signal suggesting an association between COVID-19 vaccines and SARS-CoV-2, as well as certain types of cancer.
The paper, published on January 3, 2026, in Oncotarget, includes 66 case-level reports describing 333 patients from 27 countries, two retrospective population-level investigations, and one longitudinal analysis of U.S. military personnel.
The review focused on reported cases of new cancer diagnoses, cancer progression, or recurrence occurring after COVID-19 infection or vaccination. According to the study, the most frequently reported malignancies included hematologic cancers such as lymphoma and leukemia, as well as breast, colorectal, prostate, melanoma, and brain cancers.
Co-author Wafik El-Deiry, M.D., Ph.D., told The Defender that the paper “is the first most comprehensive presentation summarizing the world‘s literature on the subject matter of COVID vaccines, COVID infection and cancer” and “look[s] like a smoking gun” linking COVID-19 shots to cancer.
In case-level reports, many patients were described as previously stable or in remission before experiencing disease progression following vaccination or infection. Others were reported to have received new cancer diagnoses within weeks or months of exposure. The authors noted that the temporal proximity of these events, combined with recurring biological themes across reports, formed the basis of the observed safety signal.
Among vaccine-related reports, the majority involved mRNA vaccines, with 56% attributed to Pfizer-BioNTech’s vaccine and 25% to Moderna. An additional 5% involved patients who had received both Pfizer and Moderna across different doses.
The review also examined population-level data. One retrospective study included in the analysis evaluated national cancer registry data and reported changes in cancer incidence trends following widespread COVID-19 vaccination campaigns. Another assessed healthcare utilization and diagnostic delays during the pandemic period. A separate longitudinal study of U.S. military personnel examined cancer diagnoses over time in relation to COVID-19 infection and vaccination status.
The paper explored several biological mechanisms that could plausibly link SARS-CoV-2 infection or vaccination to cancer-related outcomes, includeding immune dysregulation, chronic inflammation, altered T-cell responses, reactivation of latent viruses, and effects on tumor suppressor pathways. However, the authors noted that immune and inflammatory responses involving spike protein appear central to many of the reported cases.
At the same time, the researchers cautioned against overinterpretation of individual reports. Case studies are inherently limited and cannot determine risk at a population level. The review did not estimate cancer incidence rates attributable to vaccination or infection, nor did it compare outcomes against unexposed control groups in most cases. Still, the authors argued that the volume of reports and their geographic diversity justified closer scrutiny. They called for prospective studies, improved postmarketing surveillance, and greater transparency in adverse event reporting systems.
Public health agencies have consistently stated that COVID-19 vaccines are safe and effective, and there is no established evidence linking vaccination to an increased risk of cancer. The authors acknowledged this consensus but argued that emerging clinical observations should not be dismissed.
