Puma Biotechnology Inc. shares took a nosedive on Thursday in the wake of newly released data from a clinical trial for its breast cancer drug neratinib.

Shares in the Westwood biopharmaceutical firm plummeted almost 19 percent to close at $170.67 on Thursday.

The firm had released an abstract, or summary of its phase three study results, that showed an unexpectedly strong showing by the placebo group that left little room for improvement, according to a research note by Tom Shrader, a New York-based analyst with Stifel Nicolaus & Co. Inc.

Invasive disease-free survival after two years in the study was 91.6 percent for the control group (those receiving a placebo) and 93.9 percent of those who took Puma’s drug.

“It’s still a positive trial to our eyes,” Shrader wrote, noting the disease-free survival rate of those on neratinib was better than expected. It just so happened that the control group results were also much better than expected.

But Shrader also pointed out that 40 percent of neratinib patients experienced severe diarrhea, making the drug’s risk/benefit less clear.

“In other words, one in 43 women will see a benefit from taking a fairly inconvenient drug for a year,” Shrader wrote. “We still believe about 40 percent of women would consider taking neratinib.”

Puma did not immediately return a request for comment.