Detection of occult tumor cells in lymph nodes from bladder cancer patients by MUC7 nested RT-PCR

Systemic progression is the prevalent form of bladder tumor recurrence after radical cystectomy. The detection of occult bladder tumor cells in histopathologically normal lymph nodes could be of prognostic value. We examined the possibility that mucin 7 (MUC7) RNA might reflect the presence of occult tumor cells in lymph nodes from bladder cancer patients. We used the polymerase chain reaction (RT-PCR), a highly sensitive assay, to monitor MUC7 RNA.

We collected 240 pelvic lymph nodes from 25 bladder cancer patients undergoing radical cystectomy. We also obtained 20 lymph nodes from patients with prostate cancer and interstitial cystitis to use as negative controls. Each lymph node was divided in two parts to provide tissue for both histopathological and PCR analysis.

166/240 lymph nodes from bladder cancer patients were usable for MUC7 RT-PCR. By conventional histopathology, six of these nodes contained metastases. MUC7 RT-PCR analysis was positive for five of the six histologically proven lymph node metastases. Histopathological reevaluation of the sixth node revealed tumor in an adjacent vein, not in the lymph node, itself. In contrast, 46/160 (29%) histologically classified normal lymph nodes (pN0) from 17 bladder cancer patients were positive for MUC7. All 20 lymph nodes from control patients were MUC7-negative.

MUC7 RT-PCR is a specific and sensitive method for the detection of occult tumor cells in lymph nodes from bladder cancer patients. Long-term observation will be necessary to evaluate the clinical value of MUC7 as a prognostic indicator of lymph node metastasis and disease progression.