BACKGROUND Tumor metastasis involves a sequence of interrelated steps, of which penetration beyond the basement membrane is an essential component. Hyaluronic acid (HA) is a major structural component of the complex proteoglycans found in extracellular matrices and basement membranes. Hyaluronidase (PH-20) degrades HA, resulting in the disruption of basement membrane integrity and possible tumor dissemination. METHODS Total RNA was extracted from samples (n = 51) of normal breast tissue (n = 12), ductal carcinoma in situ (DCIS) (n = 12), infiltrating ductal breast adenocarcinoma (n = 13), and metastatic breast cancer to lymph nodes (n = 14). RT-PCR was used to determine the relative level of PH-20 in each specimen. RESULTS PH-20 was detected in 41/51 (80.4%) of the specimens evaluated. PH-20 was present in 12/12 (100%) normal breast tissues; 8/12 (66.7%) DCIS; 13/13 (100%) invasive breast cancers; and 8/14 (57.1%) metastases. Of those specimens in which PH-20 was detected, there were increased levels of PH-20 in metastatic breast cancer to lymph nodes compared to DCIS and invasive breast cancer. Stratification of specimen by race revealed that African American women had higher levels of PH-20 with invasive and metastatic beast cancer. CONCLUSIONS Increased levels of PH-20 are noted in invasive and metastatic breast cancer compared to DCIS. Tumors from African American women with invasive and metastatic breast cancer demonstrated higher levels of PH-20 than Caucasians. Varying levels of PH-20 in mammary tissue may contribute to early invasion and metastasis of breast cancer.