Patterns of Response and Progression to Immunotherapy

Patterns of response and progression to immunotherapy may differ from those observed with drugs such as chemotherapy and molecularly targeted agents. Specifically, some patients experience a response after progression that is retrospectively named pseudoprogression. This phenomenon of pseudoprogression, first reported in patients with melanoma who were treated with ipilimumab, has led to the development of immune-specific related response criteria, such as irRC (immune-related response criteria), irRECIST (immune-related RECIST), and iRECIST (immunotherapy RECIST) that allow continued treatment beyond progression. However, the rate of pseudoprogression has never exceeded 10% of patients across tumor types. Conversely, rapid progressions after immunotherapy, called hyperprogressions, were reported by three different teams in 9% to 29% of patients treated with immunotherapy. Because of the absence of control arms in these studies, it remains to be determined whether these rapid progressions reflect a detrimental effect of immunotherapy in these patients. Finally, preliminary data suggest that immunotherapy might also affect response to subsequent standard therapies. In total, given the rarity of pseudoprogressions across tumor types and the recent description of hyperprogressions, classic RECIST remains a reasonable and rational method to assess response to immunotherapy. Continuation of treatment beyond progression should be proposed only in carefully selected patients whose clinical conditions have improved and who have not experienced severe toxicities. Although there is an urgent need to identify predictive biomarkers of efficacy to immunotherapy, there is an equally urgent need to identify predictive factors of progression or possibly hyperprogression.