Systematic Review of Malignancy Risk with Biologic, Advanced Small-Molecule, and Thiopurine Therapies for Inflammatory Bowel Disease

Patients with inflammatory bowel disease (IBD) often require long-term immunosuppressive or advanced therapy, raising concerns about treatment-associated malignancy risk. This systematic review evaluated malignancy outcomes associated with biologic, advanced small-molecule, and thiopurine therapies in adults with IBD. PubMed, Embase, the Cochrane Library, and Web of Science were searched from inception through June 2025, with supplementary screening of Google Scholar and reference lists. Eligible primary studies included randomized controlled trials and prospective or retrospective cohort studies evaluating malignancy outcomes. Thiopurines were included because they remain clinically important comparators and are central to combination-therapy risk. The Newcastle–Ottawa Scale and the Cochrane risk-of-bias tool were used for observational studies and randomized trials, respectively. Because of substantial clinical and methodological heterogeneity, we did not perform a de novo meta-analysis; pooled estimates from previously published meta-analyses are reported only as contextual evidence. Twenty-eight studies met the inclusion criteria. Thiopurines showed the most consistent malignancy associations, including lymphoma, non-melanoma skin cancer (NMSC), acute myeloid leukemia/myelodysplastic syndrome, and urinary tract cancer. Anti-tumor necrosis factor (anti-TNF) monotherapy was not associated with a clear increase in overall cancer incidence, although a modest lymphoma signal was reported in some datasets. Combination anti-TNF plus thiopurine therapy showed the strongest lymphoma signal. Current evidence has not demonstrated an increased malignancy risk with vedolizumab or ustekinumab, including in available cohorts of patients with prior malignancy; however, confidence is limited by observational designs, small event numbers, heterogeneous cancer histories, and limited follow-up. IBD-specific data for Janus kinase inhibitors and sphingosine-1-phosphate receptor modulators remain comparatively immature, and long-term surveillance is required. Overall, treatment decisions should integrate absolute baseline risk, age, smoking, prior malignancy, prior NMSC, Epstein–Barr virus-related risk, disease-related cancer risk, and cumulative immunosuppressive exposure.