Background: Red blood cell (RBC) alloimmunization is an important complication following repeated packed RBC transfusions in patients with anemia. We aimed to determine the prevalence of RBC alloimmunization and the characteristics of the RBC antibodies among patients with solid tumors in Hospital Universiti Sains Malaysia (Hospital USM). 
Methods: A cross-sectional study was performed from May 2018 to May 2019 in the Transfusion Medicine Unit of Hospital USM, on 322 adult patients with solid tumors. The blood samples were screened for the presence of RBC alloantibodies. Samples with positive antibody screening were subjected for antibody identification. 
Results:  The mean age of the patients was 52 years old. Most were Malays (91%) and female (61.2%). The three most common cancers were breast (32.3%), gastrointestinal (16.8%) and head and neck (14.0%). The overall prevalence of RBC alloimmunization was 5.3%. Most alloimmunized patients had a single alloantibody (88.2%). The anti-Mia comprised the most common alloantibody (26.3%) followed by anti-E (10.5%) and anti-Lea (10.5%). 
Conclusion: This study showed low prevalence of RBC alloimmunization among patients with cancers. The alloantibodies were clinically non-significant. Thus, routine antibody screening and extensive RBC phenotyping in cancer patients who need multiple transfusions is not warranted.