For many years, transfusion of allogeneic red blood cells, platelet concentrates, and plasma units has been part of the standard therapeutic arsenal used along the surgical and nonsurgical treatment of patients with malignancies. Although the benefits of these blood products are not a matter of debate in specific pathological conditions associated with life-threatening low blood cell counts or bleeding, increasing clinical evidence is nevertheless suggesting that deliberate transfusion of these blood components may actually lead to negative clinical outcomes by affecting patient's immune defense, stimulating tumor growth, tethering, and dissemination. Rigorous preclinical and clinical studies are needed to dimension the clinical relevance, benefits, and risks of transfusion of blood components in cancer patients and understand the amplitude of problems. There is also a need to consider validating preparation methods of blood components for so far ignored biological markers, such as microparticles and biological response modifiers. Meanwhile, blood component transfusions should be regarded as a personalized medicine, taking into careful consideration the status and specificities of the patient, rather than as a routine hospital procedure.