The efficacy of immune checkpoint inhibitors in patients with cancer with pseudoprogression.

2620 Background: Pseudoprogression (PsP) is quite a common phenomenon in cancer patients undergoing therapy with immune checkpoint inhibitors (ICI). It could be defined as temporary increase of tumor volume or the number of tumor lesions after beginning of ICI treatment (immune unconfirmed progressive disease - iUPD) followed by clinical response. However, many specialists in real clinical practice are hesitant to continue ICI therapy in patients with iUPD because of medical or financial constraints. We aimed to evaluate the efficacy of ICI in patients with clinical evidence of PsP. Methods: We retrospectively analyzed 1001 cases of ICI treatment (male 58,4%, age 28-90 years) in patients with various solid malignancies: melanoma – 316, lung – 280, kidney – 247, GI cancer – 96, cervix of the uteri – 62. The patients were treated in 2 regional referral centers in Moscow and Moscow Region between June 2018 and Dec. 2022. Unconfirmed progressive disease (iUPD) according to iRECIST criteria was diagnosed in 316 patients at the first imaging control after the beginning of ICI treatment (31,6%). Results: Among 316 patients with iUPD the presence of progression (immune confirmed progressive disease – iCPD) was verified in 105 (33,2%): melanoma – 109 (34,5%), lung – 86 (30,7%), kidney – 75 (30,4%), GI cancer – 42 (43,8%), cervix of the uteri – 4 (6,5%). Stable disease was found in 144 (45,6%), partial response in 50 (15,8% - iPR), complete response in 17 patients (5,4% - iCR). Altogether, PsP was diagnosed in 211 of 1001 patients (21,1%). Overall objective response rate in 316 patients with iUPD reached 21,2%, control over disease was achieved in 66,8% of cases. Severe immune-mediated adverse events (3-4 st. according to CTC AE 5.0) were diagnosed in 9 patients (2,8%). Median overall survival in patients with iUPD and ORR was 16,85 mon (95% CI 15,1–18,5), in patients without iUPD and ORR – 14,93 mon (95% CI 13,78–16,0). Conclusions: PsP was diagnosed in 21,1% of patients getting ICI treatment in real clinical practice with median survival in PsP patients with objective response of about 17 months. Only 10,5% of patients had iCPD after their second follow-up. We feel that close adherence to iRECIST criteria to verify true progression is mandatory in patients under ICI treatment to exclude unnecessary cessation of treatment.