Aberrant expression of tumor suppressors CADM1 and 4.1B in invasive lesions of primary breast cancer.

BACKGROUND: The tumor suppressor genes CADM1/TSLC1 and DAL-1/4.1B are frequently inactivated by promoter methylation in non-small cell lung cancer. The proteins they encode, CADM1 and 4.1B, form a complex in human epithelial cells and are involved in cell-cell adhesion.
METHODS: Expression of CADM1 and 4.1B proteins was examined by immunohistochemistry in 67 primary breast cancer and adjacent noncancerous tissues. CADM1 and 4.1B messenger RNA (mRNA) was detected by reverse-transcription polymerase chain reaction (RT-PCR). The methylation status of the CADM1 and 4.1B promoters was determined quantitatively by bisulfite treatment followed by pyrosequencing.
RESULTS: CADM1 and 4.1B protein signals were detected along the cell membrane in normal mammary epithelia. By contrast, 47 (70%) and 49 (73%) of 67 primary breast cancers showed aberrant CADM1 and 4.1B staining, respectively. Aberrant CADM1 staining was more frequently observed in pT2 and pT3 tumors and for stages II and III (P = 0.045 and P = 0.020, respectively), while aberrant 4.1B staining was more often observed in tumors with lymph node metastasis, for pT2 and pT3 tumors, and for stages II and III (P = 0.0058, P = 0.0098, and P = 0.0007, respectively). Furthermore, aberrant CADM1 and 4.1B expression was preferentially observed in invasive relative to noninvasive lesions from the same specimen (P = 0.036 and P = 0.0009, respectively). Finally, hypermethylation of CADM1 and 4.1B genes was detected in 46% and 42% of primary breast cancers, respectively.
CONCLUSIONS: Our findings suggest that aberrant CADM1 and 4.1B expression is involved in progression of breast cancer, especially in invasion into the stroma and metastasis.