TIPIN (TIMELESS interacting protein) is a DNA replication checkpoint protein that functions as part of the TIMELESS-TIPIN complex to maintain replication fork stability and enable cell survival following DNA damage. The complex plays a central role in protecting the replisome during early S phase; it interacts directly with the replicative helicase CMG and stimulates DNA polymerase ε activity while modulating MCM helicase function 123. TIPIN is essential for the ATR-CHEK1 replication checkpoint pathway activated by replication stress or ultraviolet damage, and coordinates sister chr15 cohesion through interactions with cohesin 4. Recent evidence reveals that PARP1, TIMELESS, and TIPIN cooperatively protect replisomes from transcription-replication conflicts in early S phase, and that PARP inhibitor efficacy in homologous recombination-deficient cancers depends on this protection mechanism 5. TIPIN also suppresses local replication initiation at double-strand break sites, preventing genomic instability 6. TIPIN mutations create synthetic lethality with BRCA1 deficiency in breast cancer cells through chr15 destabilization 7, highlighting its clinical relevance as a potential therapeutic target in HR-deficient malignancies, including combination strategies with PARP inhibitors and ATR inhibitors.