Roche unit Genentech announced Friday that the Food and Drug Administration approved the injectable drug Perjeta for women with a type of breast cancer known as HER-2 positive, which makes up about a quarter of all breast cancers and has no cure.

Analysts predict the medicine could be another blockbuster cancer drug for the Swiss company.

The FDA accepted the application for the drug under priority review, meaning the agency believes the drug may represent a potentially significant advancement over existing treatments. In clinical trials, the drug kept the cancer from worsening for 6 extra months, compared to the current standard of care.

Breast cancer, the most common cancer among women worldwide, will afflict about 227,000 U.S. women in 2012, and kill about 39,500 of them, according to the American Cancer Society.

Genentech, which developed Perjeta, suffered a blow last year when the FDA revoked approval for its blockbuster drug Avastin as a treatment for breast cancer, saying the drug was not effective enough to justify its risks.

At the time, FDA advisers and other experts said Genentech should have done more trials to see exactly which subset of breast cancer patients would most benefit from the treatment.

Roche said Perjeta, known generically as pertuzumab, would only be available for women who are diagnosed with the HER2-positive form of breast cancer.

Analysts polled by Thomson Reuters have on average forecast annual pertuzumab sales of $608 million by 2016 - though some say sales could eventually climb beyond $1 billion.

Roche shares closed at 153.8 francs on Friday.

FOLLOW-ON BLOCKBUSTERS

Like other biotech drug makers, Roche is seeking to extend the longevity of its expensive brand-name medicines. Perjeta is part of that strategy, as it is a follow-on version of Herceptin, a breakthrough breast cancer drug that is the company's third-largest seller.

Herceptin, also known as tratuzumab, had 2011 global sales of $5.9 billion. The cost for a course of treatment is around $32,000.

Both Herceptin, first approved in 1998, and pertuzumab are antibodies designed to block the function of HER2, a protein produced by a cancer-linked gene. Pertuzumab binds to a different part of the same protein, which the company says makes the drug combination extra effective.

In clinical trials, women who took Perjeta in addition to Herceptin and chemotherapy had 18.5 months without their tumors growing, compared to 12.4 months for those who just took the older drugs.

Genentech is also testing Perjeta as a treatment for early-stage and advanced HER2-positive breast cancer and advanced HER2-positive stomach cancer.

Analysts at Jefferies believe the drug could reach peak sales of $8.5 billion if the company gets these additional approvals, according to a research note last week.

The company is also developing an "armed antibody" known as TDM-1 as a treatment for HER2-positive breast cancer. TDM-1 combines Herceptin with a derivative of a powerful type of chemotherapy.

(Reporting by Anna Yukhananov in Washington; Additional reporting by Adithya Venkatesan in Bangalore; Editing by Gary Hill)

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