In patients with locally advanced prostate cancer and negative results on lymph node examination, immunochemical testing of the lymph node cells can spot the spread of cancer cells that are not detected at initial tissue examination, a study shows.

Moreover, the presence of hidden prostate cancer cells that have spread (metastasized) to the lymph nodes increases the risk of recurrence and death, the study investigators report in the Journal of Clinical Oncology.

Therefore, when hidden lymph node metastases are detected in patients with locally advanced prostate cancer, “our results suggest they should be treated as high-risk patients,” advise Dr. Richard J. Cote and colleagues from the University of Southern California in Los Angeles.

They studied 274 patients with locally advanced prostate cancer who underwent surgery to remove the prostate and had cell samples taken from the lymph nodes in the groin, a common site of cancer metastases. Of these patients, 180 were diagnosed with lymph node-negative disease based on the results of routine tissue examination.

A total of 3,914 lymph nodes from the node-negative patients, an average of 21.7 nodes per patient, were then evaluated for hidden metastases using immunochemical methods, which looked for prostate-specific antigen (PSA) and certain antibodies associated with this cancer.

The results revealed hidden tumor cells in 24 patients (13.3 percent), according to the team.

Compared with patients without hidden tumor cells in the lymph nodes, the presence of these cells more than doubled the risk of prostate cancer recurrence and mortality.

These findings may have “profound implications” for the early initiation of systemic treatment after prostate cancer surgery in patients with localized prostate cancer and whose lymph nodes appear to be negative using routine tissue analysis, Cote and colleagues conclude.

SOURCE: Journal of Clinical Oncology, June 20, 2006.