UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase 6 (ppGalNAc-T6) mRNA as a potential new marker for detection of bone marrow-disseminated breast cancer cells.

The evaluation of disseminated epithelial tumor cells in patients with early stages of breast cancer has generated considerable interest because of its potential association with poor clinical outcome. Considering that O-glycosylation pathways are frequently altered in breast cancer, we performed this work to evaluate the potential usefulness of UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts) (a family of glycosyltransferases which catalyze the first key step of mucin-type O-glycosylation) to detect disseminated cells in bone marrow samples from patients with operable breast cancer. Using RT-PCR assays, we studied the gene expression of 9 enzymes (ppGalNAc-T1-T9). Among the ppGalNAc-Ts expressed by breast tumors (-T1, -T2, -T3, -T6 and -T7), the best specificity (negative results on all PBMN cell samples from healthy donors) was shown for ppGalNAc-T6. Thus, we selected this enzyme as a target gene for further evaluation. ppGalNAc-T6 mRNA was found in 22/25 (88%) breast cancer samples, in all 3 human breast cancer cell lines evaluated (MCF-7, ZR75-1 and T47D), in 1/30 (3%) PBMN cells and 0/19 bone marrow samples obtained from patients without cancer. Using this method, 22/61 (36%) patients with breast cancer, who underwent curative surgery, showed positive ppGalNAc-T6 mRNA in bone marrow aspirates obtained prior to surgery, including 11/34 patients with stage-I or -II, without histopathological lymph node involvement. In a preliminary follow-up evaluation, 19/61 patients experienced recurrence of the disease. ppGalNAc-T6 was positive in 11/19 (57.9%) of these patients. Interestingly, in the group of patients without lymph node involvement, disease recurrence was observed in 54.5% of patients who showed ppGalNAc-T6 mRNA-positive bone marrow aspirates and only in 4.3% of patients when ppGalNAc-T6 was negative (p = 0.014). These results indicate that ppGalNAc-T6 mRNA could be a specific marker applicable to the molecular diagnosis of breast cancer cells dissemination.