Methylthioadenosine phosphorylase in human breast cancer.

Methylthioadenosine (MTA) phosphorylase activity was measured in 47 biopsies from primary breast cancers (n = 34) and metastatic tumors (n = 13). Most specimens were also evaluated by DNA flow cytometry and determination of estrogen and progesterone receptor contents. Median MTA phosphorylase activity was 317 pmol/mg protein/min (range 50-1312 pmol/mg protein/min), but great variations were observed. Samples from four individuals had very low MTA phosphorylase activity (less than or equal to 70 pmol/mg protein/min). No correlation with aneuploidy, receptor status, or the presence of metastases in the lymph nodes could be demonstrated. However, MTA phosphorylase activity showed a significant (p = 0.009) negative correlation with the fraction of cells in the S-phase of the cell cycle.