Introduction: There are about 60,000 diagnoses of cancer per year in Belgium. After hospital care, about 12–13% of cancer patients are readmitted within 30 days after discharge. These readmissions are partly related to drug-related problems (DRP), such as interactions or adverse drug effects (ADE). Objectives: The aim of this study is to quantify and to classify DRP readmissions within 30 days for cancer patients and to highlight risk factors potentially correlated to readmissions. Methods: This study is a 6-month observational retrospective study in two care facilities in Brussels: an academic general hospital and an academic oncology center. Patients readmitted within 30 days after their last hospital care for a potential DRP were included. Patient files were evaluated with an intermediate medication review that included interactions analysis (Lexicomp®). The probability of DRP readmission was assessed using the World Health Organization’s Uppsala Monitoring Centre (WHO-UMC) system. Results: The final population included 299 patients; among them, 123 (41.1%) were readmitted due to DRP (certain DRP (4.9%), probable DRP (49.6%), and possible DRP (45.5%)). Risks factors linked to these DRP were a low Charlson Comorbidity Index, polypharmacy, the kind of hospital, and some chemotherapies (platinum preparations). Among all readmitted patients, the D-type interactions were the most common (44.8%), which suggest a possible therapy modification. However, around 10% of interactions were X-type (drug combination to avoid). Conclusion: Almost 10% of patient readmitted within 30 days were potentially related to a DRP, most of them from adverse drug effects. Four risk factors (low Charlson Comorbidity Index, polypharmacy, the hospital, and some chemotherapies) were highlighted to prevent these readmissions. ; SCOPUS: ar.j ; info:eu-repo/semantics/published