of hyaluronidases in cancer has been historically controversial due to contradictory observations, namely that levels of hyaluronidase (HYAL1/2) are increased in some cancers (colorectal, bladder, prostate, breast and brain), whereas low expression of HYAL1 is correlated with a decrease in survival of pancreatic adenocarcinoma patients. The reason for this apparent contradiction is that both the accumulation of HA (due to increased HAS levels and decreased HYAL levels), and the degradation of HA into HA oligosaccharides by high HYAL levels result in increased tumor malignancy. Elevated tissue expression of hyaluronic acid and hyaluronidase validates the HA-HAase urine test for bladder cancer. Limited data support a role of lysosomal hyaluronidases in metastasis, while other data support a role in tumor suppression. Other studies suggest no contribution or effects independent of enzyme activity. Non-specific inhibitors (apigenin, sulfated glycosaminoglycans) or crude enzyme extracts have been used to test most hypotheses, making data difficult to interpret. It has been hypothesized that, by helping degrade the ECM surrounding the tumor, hyaluronidases help cancer cells escape from primary tumor masses. However, studies show that removal of hyaluronan from tumors prevents tumor invasion. Hyaluronidases are also thought to play a role in the process of angiogenesis, although most hyaluronidase preparations are contaminated with large amounts of angiogenic growth factors. Role in pathogenesis Some bacteria, such as Staphylococcus aureus, Streptococcus pyogenes, and Clostridium perfringens, produce hyaluronidase as a means of using hyaluronan as a carbon source. It is often speculated that Streptococcus and Staphylococcus pathogens use hyaluronidase as a virulence factor to destroy the polysaccharide that holds animal cells together, making it easier for the pathogen to spread through the tissues of the host organism, but no valid experimental data are available to support this hypothesis. Hyaluronidases are found in the venom of certain lizards and snakes, as well as honeybees, where they are referred to as "spreading factors", having a function akin to bacterial hyaluronidases. Role in immune response White blood cells produce hyaluronidase to move more easily through connective tissue to get to infected sites. Role in fertilization In mammalian fertilization, hyaluronidase is released by the acrosome of the sperm cell after it has reached the oocyte, by digesting hyaluronan in the corona radiata, thus enabling conception. Gene-targeting studies show that hyaluronidases such as PH20 are not essential for fertilization, although exogenous hyaluronidases can disrupt the cumulus matrix. The majority of mammalian ova are covered in a