Radioimmunoconjugates in the age of modern immuno-oncology

Immunotherapy was first investigated as a therapeutic option for treating cancer more than a century ago. During this period, it has gone through numerous disappointments when the successes obtained in the laboratory were not matched clinically. However, recent advances in immuno-oncology have provided the impetus to revisit this therapeutic option. Unlike previous efforts, modern immunotherapy is now a realistic and formidable therapeutic option for patients with relapsed/refractory malignancies. Unfortunately, most of the successes obtained thus far have primarily been in patients with hematologic malignancies. While the results of immunotherapy with immune check-point inhibitors for solid tumors such as non-small cell lung cancer and melanoma are encouraging, more effective treatment methods are desirable. Many intrinsic and extrinsic factors pose as obstacles to successful immunotherapy of solid tumors. They include heterogeneity of tumor antigens, limitation in the trafficking and accessibility of the effector mechanisms to the tumor sites, the adverse anti-inflammatory tumor microenvironment, and the on-target off tumor and off-target off-tumor effects of some of these approaches. In this review, we will discuss these obstacles and examine the evidence that support the notion that radioimmunotherapy, using radioimmunoconjugates, may be the answer to overcome these obstacles in patients with metastatic cancer. Finally, we will discuss how the efficacy of radioimmunotherapy using radioimmunoconjugates might further be harnessed to maximize successes in these patients.