Detection of regional lymph node metastases in colon cancer by using RT-PCR for matrix metalloproteinase 7, matrilysin.

Lymph node metastasis is the most important prognostic factor in colon cancer. However, more accurate screening for metastasis than that afforded by conventional pathology remains elusive. We have employed a reverse transcriptase-polymerase chain reaction (RT-PCR) assay for a matrix metalloproteinase (MMP), 'matrilysin', because this gene is epithelial-specific and consistently expressed in colorectal cancer cells. The sensitivity of this assay was examined with the matrilysin-producing rectal cancer cell line 'CaR-1'. Matrilysin mRNA was detected in this system when more than 10(4) matrilysin-positive cells existed in a lymph node of ordinary size. Fourteen of 15 (93%) primary colon cancers and none of the surrounding normal tissues expressed matrilysin. All 10 histologically-positive lymph nodes were positive for matrilysin, while of 60 histologically-negative lymph nodes, eight were positive for matrilysin. When the additional sequential sectioning and histological re-examination was performed on five of these eight 'matrilysin-positive, but histologically-negative' lymph nodes, micrometastases were detected in three. Only one of the lymph nodes that were histologically-positive, but negative by matrilysin assay was from a patient with colon cancer in which matrilysin was not detected. In conclusion, RT-PCR assay for matrilysin is a sensitive method for detecting occult metastases in patients with colon cancer, and may complement histologic examination.