Figure 9c.

Pseudoprogression after initiation of nivolumab in a 69-year-old man with metastatic clear cell RCC. (a) Baseline axial CT image of the chest shows several right pulmonary metastases (arrows), which had enlarged when compared with prior images (not shown). (b) Axial CT image from a follow-up examination 1 month after treatment with nivolumab shows continued enlargement of the pulmonary metastases (arrows). Images of the abdomen at that time also showed new hepatic and pancreatic metastases (not shown). Given these findings and poor performance status, the patient decided to forego further treatment and pursue hospice care. After 6 months, the patient returned to clinical care with substantially improved performance status. (c) Axial CT image obtained at that time shows substantial improvement in pulmonary disease. Several of the pulmonary metastases previously visualized in the right middle and lower lobes are no longer seen. The hepatic and pancreatic metastases had decreased substantially in size (not shown). The rapid enlargement on the initial follow-up image in b is in keeping with pseudoprogression, which is the result of a transient inflammatory infiltration to the tumor by immune cells and a part of the pathophysiology of response for immune checkpoint inhibitors.