Immunotherapy has lately emerged as a very effective anticancer therapy applied in fighting different types of resistant tumors using immune checkpoints blockade. New patterns of tumor responses have been observed following immunotherapy: an aggressive progression of disease and acceleration in tumor growth coupled with clinical deterioration known as hyperprogression and a transient tumor progression followed by a response to treatment known as pseudoprogression. Although many explanations were proposed to unfold the physiology behind these two phenomena and their underlying biological mechanisms, our understanding of these patterns of response is still limited. This is mainly due to the heterogeneity among studies in the tumor types, treatment modalities, and implemented therapeutic agents and to the lack of consensus on unified diagnostic criteria. It is important to differentiate between these two types of responses to avoid the harm to patients in the case of hyperprogression and the unnecessary discontinuation of treatment in the case of pseudoprogression. Therefore, it is necessary to further investigate these patterns by setting consensual diagnostic criteria. In this review, we define hyperprogression and pseudoprogression, and we present the latest findings that discuss the underlying pathophysiology, predictive factors, current diagnostic criteria, and plans of treatment beyond progression.