Shares of Westwood drug developer Puma Biotechnology plummeted in trading on Monday after presentations by the company and another drugmaker soured investors on their prospects.

Puma released its most recent phase two trial results for its cancer drug neratinib. The company’s stock was also hurt by the release of disappointing phase three trial results for a breast cancer drug being developed by British pharmaceutical giant GlaxoSmithKline. Puma and GlaxoSmithKline presented their results over the weekend at the American Society of Clinical Oncology conference in Chicago.

Puma touted its results as positive, but investors have shown they’re not as pleased. The trial results showed that three of 40 patients with breast cancer that had already metastasized to the brain had a partial response to the drug, or a decrease in their cancer, after taking neratinib. The results also showed that diarrhea was a common side effect of the drug.

GlaxoSmithKline disclosed that its cancer drug tykerb, when combined with existing cancer drug herceptin, did not improve outcomes for patients in a phase three trial, compared with taking just herceptin.

Puma said it is continuing trials with two other groups of patients.

Puma shares fell 25 percent in Monday trading on the New York Stock Exchange to $57.