Proliferative potential of brain metastases.

Thirteen patients with metastatic brain tumors received an intravenous infusion of bromodeoxyuridine (BUdR) 200 mg/m2 at craniotomy) to label S-phase tumor cells. Excised tumors were stained immunohistochemically for BUdR. The percentage of BUdR-positive cells was calculated to determine the BUdR labeling index (LI) (or fraction of S-phase cells), which provides an estimate of the proliferative potential. Histologically, 11 patients had adenocarcinoma (four well-differentiated, three moderately differentiated, and four poorly differentiated), one had a large cell carcinoma, and one had a small cell carcinoma. All tumors had a BUdR LI greater than 5% (mean, 13.3 +/- 7% standard deviation). Moderately and poorly differentiated adenocarcinomas had a higher LI than well-differentiated adenocarcinomas (median, 15.3% versus 8.2%). These LI values are considerably higher than those reported for primary tumors with comparable histologic features. Thus, metastatic tumors in the brain may grow faster than the primary tumors from which they originate.