Puma Biotechnology Inc. might have been a little too optimistic.

The Westwood company, whose sole product is neratinib, a drug for the treatment of breast cancer, had expected to file study data with the Food & Drug Administration after its new drug application.

But the FDA didn’t like that timing. Instead, it asked for the data, from a study to see whether neratinib is linked to an increased risk of secondary cancer, at the time the application is submitted. That led the company to announce last week that it would delay the filing, which was expected in the next six months, to the first quarter of 2016. The news sent shares of the company down 12 percent to close at $197.67 on Wednesday, making it one of the biggest losers on the LABJ Stock Index. (See page 28.)

Puma originally believed that neratinib’s first use would be for patients with a more progressed form of the cancer whose life expectancy was just a year or two. That would have allowed the company to forgo a study on increased risk of developing a secondary cancer over the long term. But neratinib’s Phase III trial showed positive results in the early stage breast cancer patient population in July. In those cases, the FDA requires the studies to be submitted with the application.

In a conference call with analysts last week to discuss the news, Chief Executive Alan Auerbach acknowledged that other drugs approved for treatment of early breast cancer all submitted the result from their carcinogenicity studies either before or at the time of their application filing.

Yatin Suneja, an analyst in the New York office of Cowen & Co., said Puma’s management team might have gotten a little bit carried away.

“They should have realized when they changed their strategy, the FDA will not budge,” he said.

Still, he called the news not a big issue.

“We still think it’s going to get approved and has the potential of a $5 billion-plus drug,” Suneja said. “We need to wait another nine to 12 months.”

The decline in share price, he added, was to be expected. Some investors see that revenue won’t be coming as early as they thought, and not everybody intends to hold a stock for the long term.

Puma shares skyrocketed nearly 300 percent in July on news of neratinib’s Phase III clinical trials resulting in test participants having a 33 percent better disease-free survival rate than those who were given a placebo. The bump made Auerbach L.A.’s newest billionaire at the time, as his 6.4 million shares, warrants and options were worth about $1.5 billion. Those shares were worth $1.25 billion at last week’s lower price.