High baseline lymphocyte count is a predictive biomarker of prolonged time to progression in patients with advanced solid tumors receiving checkpoint inhibitors.

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e14532 Background: Biomarkers predicting response to checkpoint inhibitor are needed to better select patients most likely to benefit from treatment. We observed that baseline absolute lymphocyte count (ALC) can predict durable responses to anti-PD-1 antibodies in various malignancies. Methods: This is a retrospective analysis of patients with advanced solid tumors treated with anti-PD-1 antibodies. Pembrolizumab was given at 2 mg/kg every 3 weeks, Nivolumab at 3 mg/kg every 2 weeks. Peripheral ALC and absolute neutrophil count (ANC) from routine safety labs were collected at baseline, cycle 4 and cycle 8. Evaluation of response was based on irRECIST. Neutrophil lymphocyte ratio [NLR = ANC/ALC] was stratified by ≤4 or > 4. The lymphocyte count cutoff was 1000/mm3. Time to progression (TTP) and overall survival (OS) were estimated with the Kaplan-Meier method. Differences between groups were estimated with the log rank test. Results: We have retrospectively evaluated 40 patients with unresectable stage III/IV Non Small Cell Lung Cancer (squamous n. 17; 42.5%, adenocarcinoma n. 7; 17.5%), Malignant Melanoma (n.11; 27.5%), Renal Cell Carcinoma (n.5; 12.5%) treated with anti-PD-1 antibodies. 6 pts (15%) received treatment as 1st line, 14 pts (35%) as 2nd line, 20 pts (15%) as ≥ 3rd line. We observed a 29% partial response (PR), 31% stable disease (SD) and 40% progressive disease (PD). The overall response rate (ORR) was 29% [I.C. 95% 13-42]. Median TTP was 5.5 months [IC 95% 3.3-NR]. Median OS was not reached. Pts with baseline ALC ≥1000/mm3 had significantly longer TTP (median value not reached), compared with those who had ALC < 1000/mm3 (median TTP 2.8 months), p = 0.01. There was also a trend for longer TTP in patients with NLR < 4 vs ≥4 (4.9 vs 10.5 months, p 0.44). Conclusions: In our observation baseline ALC ≥1000/mm3 is a predictive biomarker of prolonged TTP in patients treated with anti-PD-1 antibodies. The potential predictive value of this test should be prospectively validated.

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