SOLUBLE CD44 V5 AND V6 IN SERUM OF PATIENTS WITH BREAST-CANCER - CORRELATION WITH EXPRESSION OF CD44 V5 AND V6 VARIANTS IN PRIMARY TUMORS AND LOCATION OF DISTANT METASTASIS

Primary breast cancers were shown to overexpress CD44 v5 and v6 at the plasma membrane. However, the clinical significance of this overexpre ssion remains unclear. Overexpression of CD44 v5 and v6 in primary bre ast cancers was found to correlate with metastasis and poor prognosis by some investigators, yet this correlation could not be confirmed by others using different antibodies. In this study the influence of meta static disease, the site of metastasis, and the amount of CD44 v5 and v6 expression in the primary tumor on serum levels of the soluble form s of CD44 v5 and v6 (sCD44 v5 and v6) in breast cancer patients was in vestigated. Soluble CD44 v5 and v6 serum levels were measured by enzym e linked immune sorbent assay in a ,ans and in another group of patien ts group of breast cancer patients who developed metastases in various organs with single organ metastasis. For control, sCD44 v5 and v6 lev els were measured in breast cancer patients who remained free of metas tasis and in healthy blood donors. Expression of plasma membrane bound CD44 v5 and v6 in the primary tumors of the patients with metastasis in various organs was correlated to sCD44 v5 and v6 levels in serum. F urthermore the size of sCD44 v6 was analyzed by immunoblot using a mon oclonal antibody directed against CD44 v6. When metastases were detect ed: sCD44 v5 and v6 serum levels were increased as compared to levels measured one month after tumor surgery in patients free of metastases (p = 0.0025 and p = 0.0004). Six of 19 and 6 of 20 patients had sCD44 v5 and v6 serum levels above a cut-off level of 85 and 275 ng/mL, resp ectively. In these cases expression of CD44 v5 and v6 in the primary c ancers was also elevated. Low sCD44 v5 and v6 serum levels were associ ated with weak expression of CD44 v5 and v6 in the respective primary cancers. As shown by statistical analysis of sCD44 v5 and v6 levels in 57 patients with single organ metastases, elevated sCD44 v6 levels bu t not sCD44 v5 levels were associated with metastases in liver or bone (p = 0.0025). Immunoblot analysis of soluble CD44 proteins in serum r evealed two CD44 v6 specific signals of approximately 120 and 170 kDa. Increased sCD44 v5 and v6 serum levels in patients with breast cancer were influenced by the amount of CD44 v5 and v6 expression in the pri mary tumor by the site of metastasis. Elevated sCD44 v6 serum levels w ere preferentially found in patients with metastases in liver or bone.