[Tumor assessment in immune checkpoint inhibitor therapy : Tumor response, progression and pseudoprogression]

In contrast to chemotherapy, treatment with immune checkpoint inhibitors occasionally results in an unconventional pattern of response. Besides an early partial or complete response or tumor progression, a so-called pseudoprogression, a "mixed response" or late responses can also be observed. Treatment beyond radiographically defined progression may therefore be appropriate in selected cases. For these treatment decisions, the clinical evaluation of the patient (performance status, symptoms, etc.), the "dynamics" of the underlying malignancy, and the availability of other treatment options are of paramount importance. However, the time to initiate another treatment should not be missed by rapid progression. In PD-1 (programmed cell death protein 1) immune checkpoint inhibition in urothelial cancer after platinum-based chemotherapy, response or progression can be observed early at week 8 in the vast majority of the cases. In contrast, in second-line treatment of renal cell carcinoma around 25% of responses are seen late, at week 24 or later (occasionally after 1 year). Therefore, immune checkpoint inhibition should be continued for stable disease. At present, it remains unclear how long to continue therapy in cases with partial or complete remission.