The Roche AG (RHHBY) breast cancer drug Perjeta notched an important win in the closely followed "Aphinity" clinical trial, promising to add billions of dollars in sales to the Swiss drugmaker's top line.

Perjeta's success spells big trouble for Puma Biotechnology (PBYI) - Get Report , which could see its competing, but still unapproved, breast cancer drug neratinib without any patients to treat.

Roche gained more than 5.2%, the biggest single-day advance in at least a year, to change hands at a seven-month high of Srf259.1 each and rose to the top of the benchmark SMI index in Zurich.  Puma shares are down 20% to $30.45 in pre-market Nasdaq trading. 

In a statement Thursday, Roche said breast cancer patients treated with Perjeta combined with Herceptin and chemotherapy after surgery (the adjuvant setting) had a lower risk of death or the return of their tumors compared to patients treated with Herceptin and chemotherapy alone. Roche did not disclose the magnitude of the Perjeta benefit demonstrated in the "Aphinity" study on Thursday. Those important details will likely be presented at the ASCO cancer conference in June. 

"These results from the positive APHINITY study represent an important addition to the body of data for Perjeta in the treatment of people with HER2-positive early breast cancer," said Sandra Horning, Chief Medical Officer and Head of Global Product Development at Roche. "We look forward to discussing these adjuvant results with global regulatory authorities."

Roche was counting on a successful outcome from the "Aphinity" study to grow Perjeta sales and defend its mainstay Herceptin breast cancer drug from looming generic competition. Herceptin generated around Sfr6.78 billion ($6.7 billion) in sales for Roche last year, up 4% from 2015, while Perjeta had top line growth of 26% last year to Sfr1.85 billion.

"Current Herceptin monotherapy treatment is already highly successful and represents a high hurdle to beat which makes the positive "Aphinity" outcome all the more impressive," analysts at Jeffries said Thursday. "Nonetheless, for the Perjeta / Herceptin combination to become widely used as a new standard of care, we will likely need to see a strong clinical benefit demonstrated by the data, as well as the statistically significant benefit."

Analysts from Berenberg in London said the HER2 franchise -- Herceptin and Perjeta -- is likely to grow from Sfr9.5 billion last year to around Sff11.4 billion in the next five years.

Puma finds itself on the losing side of the positive Perjeta study outcome.

The Los Angeles-based biotech company is seeking FDA and European approval for neratinib as an extended adjuvant breast cancer therapy. That means treating post-surgery breast cancer patients first with one year Herceptin/chemo (standard adjuvant therapy) and then switching them to one year of neratinib.

But with the "Aphinity" study success, Perjeta/Herceptin is likely to becomes the new standard of care for adjuvant breast cancer therapy. That squeezes out neratinib, in part because there are no data to support the use of neratinib after Perjeta/Herceptin. Even without the Perjeta competitive risk, Neratinib's approval chances were weighed down by clinical data demonstrating a small benefit for breast cancer patients and extremely high rates of serious diarrhea.

Puma had no comment yet Thursday but in the past, CEO Alan Auerbach has insisted neratinib is still viable even with the addition of Perjeta to adjuvant breast cancer therapy.

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