Shares of Puma Biotechnology Inc. took a huge leap this week after stage two trials of the Westwood company’s cancer drug produced results better than analysts had expected.

Puma announced Dec. 4 that its sole product, Neratinib, was more effective in treating cancers of the breasts and lymph nodes in a small sample of preoperative patients than an established drug, Herceptin. The trials paired both drugs with chemotherapy.

Wall Street analysts weren’t expecting Neratinib to outperform Herceptin. The surprise made Puma the biggest gainer on the LABJ Index. (See page 26.) Shares closed at $80.89, up 75 percent for the week and 320 percent for the year.

“The expectation was that Neratinib would be equally as efficacious (as Herceptin),” said Eric Schmidt, an analyst who follows Puma at Cowen Group in New York. “But to beat it, by a not insignificant amount, it got people thinking about what may be a larger opportunity.”

The trial was the latest hurdle to clear for Puma, a company led by Chief Executive Alan Auerbach, a biotechnology entrepreneur and former Wall Street analyst, as the company sets its sights on approval by the Federal Drug Administration.

Auerbach sold his previous company, drug developer Cougar Biotechnology, to Johnson & Johnson for about $1 billion in 2009. Cougar’s Zytiga was approved for treatment of late-stage prostate cancer in 2011.

After the Cougar sale, Auerbach raised funds from investors to purchase the intellectual property and know-how behind Neratinib from Pfizer Inc. for about $185 million in 2011. Puma paid some of the purchase price upfront and the rest is being paid out at predetermined milestones. Most of Puma’s staff of 75 previously worked for Auerbach at Cougar.

Next up for Puma is a phase three trial of Neratinib, to begin next year on a larger sample size of patients. Schmidt said the trial will be more complex than phase two, and will likely also include results of treatments with newly approved breast cancer drug Perjeta in some form. Still, he believes Puma’s likelihood of success in phase three is quite high.

Auerbach said he’s still deciding whether Puma would take the drug to market on its own or with a joint venture partner, or whether he would look to sell the company as he did with Cougar. He did say, however, that he’ll do what’s in the best interest of his investors.

Auerbach owns about 20 percent of shares, which were valued at $469 million last week.

“The plan is to do what is in the best interests of the stockholders,” he said.