Immunotherapy in Special and Rare Situations: A Brief Review

Immunotherapy has established itself as an important component of the treatment armamentarium against various solid as well as hematologic cancers. Immune checkpoint inhibitors (ICI) provide for a very well-tolerated and efficacious treatment option that has improved survival in several cancers. The approved ICIs mainly consist of antibodies targeting cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) or its ligand, programmed cell death ligand 1 (PD-L1). However, most clinical trials of ICI have excluded patients from high-risk populations, such as those with autoimmune diseases, patients on chronic steroid intake for various reasons or preexisting HIV infections. The older adults are also an underrepresented section of the population enrolled into such trials, most probably due to the higher prevalence of comorbidities and frailty affecting their Eastern Co-Operative Oncology Group performance status, and thus the eligibility for clinical trial enrollment. This paper aimed to briefly review the available evidence and thus guide the decision-making process for use of ICI in such rare and special situations.