CCDC170 (coiled-coil domain containing 170) is a protein involved in cytoskeletal organization and cellular signaling with significant implications for bone metabolism and breast cancer. The protein plays a role in Golgi-associated microtubule organization and stabilization, contributing to cellular structural integrity [UniProt]. In bone biology, CCDC170 positively regulates bone formation, with knockdown studies demonstrating its importance in maintaining bone mineral density 1. The gene is subject to post-transcriptional regulation by multiple microRNAs (miR-153-3p, miR-374b-3p, miR-4274, miR-572, and miR-2964a-5p) through allele-specific binding at polymorphic sites 1. In breast cancer, CCDC170 exhibits tumor suppressor-like properties, promoting apoptosis through the IRE1α pathway and correlating with better disease-free survival 2. However, ESR1-CCDC170 gene fusions, found in 6-8% of luminal B breast cancers, confer endocrine therapy resistance by activating HER2/HER3/SRC/AKT signaling pathways 3. Genetic variants in the CCDC170/ESR1 locus are associated with osteoporosis risk, breast cancer susceptibility, and bone mineral density regulation 456. The protein's expression is also detected in reproductive tissues, particularly fallopian tube epithelial cells 7.