FAM170B (family with sequence similarity 170 member B) is a testis-specific acrosomal protein with primary roles in male reproduction. During spermiogenesis, FAM170B localizes to the perinuclear region adjacent to the Golgi and acrosome in elongating spermatids and mature spermatozoa 1. The protein interacts with GOPC (Golgi-associated PDZ and coiled-coil motif containing protein) during acrosome formation 1, and anti-FAM170B antibodies specifically inhibit the acrosome reaction in vitro 1, indicating a functional role in fertilization. However, CRISPR/Cas9-generated Fam170b knockout mice produced normal litter sizes with no defects in sperm counts, motility, or morphology, demonstrating that FAM170B is dispensable for male fertility in mice 2. This contrasts with FAM170A, its paralogous protein, which is essential for male fertility 2. Beyond reproduction, FAM170B-AS1 (an antisense transcript) has emerged as a potential disease biomarker. This lncRNA is upregulated in breast cancer sera and associated with cancer stage, grade, and lymph node metastasis 3. FAM170B-AS1 was also identified as a novel locus susceptible to early-onset coronary artery disease in Japanese populations 4. These findings suggest FAM170B has context-dependent biological functions with potential clinical significance in cancer diagnosis and cardiovascular disease risk assessment.