Shares of

Schering-Plough

(SGP)

slipped Friday, in reaction to the announcement after the market closed Thursday that the company had stopped enrolling patients in a test of an experimental drug for treating nonsmall lung cancer.

Recently, shares of the Kenilworth, N.J.-based drugmaker had lost 26 cents, or 1.4%, to trade at $18.71.

The company said it had stopped enrolling patients in a phase III trial of Sarasar because an analysis of interim data "led to the conclusion that the study will not provide sufficient evidence of efficacy to warrant further enrollment." Phase III is the last clinical study of drugs conducted by companies before they seek marketing approval by the Food and Drug Administration.

Schering-Plough said it would continue to study Sarasar in other types of cancer. The company is in the midst of Phase II clinical tests of the drug for treating leukemia and several solid tumors.