STK33 is a serine/threonine kinase primarily characterized by its essential role in male fertility. In spermatogenesis, STK33 phosphorylates fibrous sheath proteins AKAP3 and AKAP4, regulating sperm flagella assembly and axonemal structure 1. Loss-of-function STK33 mutations cause male infertility through defective sperm morphology and motility, with homozygous mutations resulting in sterility and heterozygous mutations causing oligoasthenozoospermia 1. STK33 inhibition produces reversible, nonhormonal contraceptive effects in mice without systemic toxicity 2. Beyond reproduction, STK33 contributes to cancer progression across multiple tumor types. In pancreatic neuroendocrine tumors, STK33 overexpression correlates with poor prognosis and activates the PI3K/AKT/mTOR proliferation pathway 3. In triple-negative breast cancer, STK33 is highly expressed and promotes tumor growth by phosphorylating and stabilizing CCAR1 4. In neuroblastoma, STK33 suppression via miR-454-3p induces apoptosis and autophagy 5. Additionally, STK33 is expressed in fallopian tube epithelial cells and associated with ovarian cancer risk 6. These findings establish STK33 as both a validated male contraceptive target and an emerging therapeutic target for multiple malignancies.