After years of setback, cancer immunotherapy has begun to yield clinical dividends, which are changing the treatment landscape and offering cancer patients the potential for long-term survival, reduced treatment-related toxicity and improved quality-of-life. Using the immune system to treat cancer is known as 'Immuno-oncology' (IO) and agents are sub-classified by their ability to enhance anti-tumor response or to direct the immune system to attack cancer cells via tumor-associated antigens. Areas covered: Clinical trials have demonstrated the effectiveness of several IO agents in many disease sites such as early and advanced stage melanoma, advanced non-small cell lung cancer, bladder, head and neck, gastric, kidney as well as Hodgkin's lymphoma. Notwithstanding the therapeutic excitement generated for patients and clinicians alike, an important consideration is treatment cost, which can reach more than $US100,000 per patient annually. The cost of the drugs, coupled with high disease prevalence and the ever-expanding number of indications, means the current cost trajectory is untenable for most healthcare systems to sustain. Expert commentary: In this paper, the approved IO drugs and those in clinical development are reviewed. The issue of cost effectiveness vs. affordability is then addressed and suggestions that facilitate patient access and long-term sustainability are presented.