https://www.selleckchem.com/products/acetohydroxamic-acid.html Immune checkpoint inhibitor (ICPis) re-challenge could be an attractive therapeutic option considering its good safety profile. However, little data is available regarding anti-PD-1/anti-PD-L1 retreatment. We conducted a meta-analysis focusing on outcomes of solid cancer patients performing this strategy. Fourteen full papers involving 74 patients were included. Individual data about best response or progression-free survival (PFS) upon the first and second course of anti-PD-1/anti-PD-L1 were collected. Non-small-cell lung cancer (53%) and melanoma (34%) were the most represented cancers. Higher objective response (46% versus 24%, P=4.10 ) and disease control rates (73% versus 52%, P=7.10 ) were obtained upon the first ICPi course compared to re-challenge. No association between responses obtained with the two ICPis courses was found (P=3.10 ). The PFS upon the first ICPi (PFS1) was longer than after re-challenge (PFSR) (6.6 versus 2.8 months, hazard ratio (HR) 0.57, P=2.10 ). A longer PFSR was obtained in patients with a longer PFS1 (P=6.10 ), in those who discontinued the first ICPi due to toxicity or per protocol (8.8 versus 2.1 months if disease progression occurs, P=2.10 ), and in those not receiving intercalated treatment between the two ICPis (6.6 versus 2.1 months for the treated ones, P=1.10 ). Anti-PD-1/anti-PD-L1 re-challenge showed interesting clinical activity in selected patients, mainly in those achieving a long-term response upon the first ICPi course, that do not discontinue therapy because of disease progression, or that are able to keep a treatment-free period. Anti-PD-1/anti-PD-L1 re-challenge showed interesting clinical activity in selected patients, mainly in those achieving a long-term response upon the first ICPi course, that do not discontinue therapy because of disease progression, or that are able to keep a treatment-free period. To evaluate the effect of testosterone treatment