Biopharmaceutical company NeoPharm Inc. said Monday that in a clinical trial its experimental treatment for malignant tumors of the central nervous system didn't prove to be more effective than an existing treatment.

Shares of the company tumbled on the news, shedding $4.69, or 69.7 percent, to $2.03 in morning trading on the Nasdaq. Earlier in the session, the stock slumped to a fresh 52-week low of $1.80, well below its prior trough of $4.32.

The company said it was evaluating cintredekin besudotox for the treatment of recurrent glioblastoma mulitforme against Gliadel Wafer, which is implanted in the cavity the tumor once occupied after surgery. The wafer is made by MGI Pharma Inc.

Neopharm said its drug didn't show a statistically significant difference in the overall survival cures of patients with the tumors in a Phase III trial.

The company said it would work with its scientists and regulators to decided the best path forward for the drug.