Dissociated Responses in Patients with Metastatic Solid Tumors Treated with Immunotherapy

Background Immune checkpoint inhibitors have been demonstrated to improve overall survival. Atypical patterns of response have been reported, including dissociated response (DR). We evaluated the prevalence of DR. Patients and methods Patients had to have a baseline computed tomography (CT) scan and at least one follow-up CT scan and two target lesions (TLs). Three types of DR were evaluated using RECIST1.1: DR1, defined as at least one progressive and one responding TL; DR2, defined as at least one progressive and one stable TL; and DR3, defined as at least one stable and one responding TL. Results A total of 1244 measurements of 272 TLs were performed in 100 patients. Forty-nine out of the 272 TLs (18%) had received old or recent radiotherapy, and 42 (15%) had been biopsied. An objective response was observed in 22 patients (22%) and on 52 TLs (19%). DR1 were observed in 8% of patients. At the tumor measurement level, the response rate was lower in the case of prior radiotherapy (29% vs 34%, p = 0.01) and higher in the case of prior biopsy (40% vs 32%, p = 0.02). Conclusions A DR was observed in 8% of patients. Response rate was lower in the case of prior radiotherapy and higher in the case of prior biopsy.