UPDATE 1-Pfizer drug has long-term edge over tamoxifen-data

* Women switching drug have better outcome for next 6 years

* 18 pct more likely disease-free, 14 pct less likely to die

(Adds details, background)

BERLIN, Sept 22 (Reuters) - Switching breast cancer patients onto Pfizer's PFE.N Aromasin half way through a five-year course of tamoxifen improves their chance of staying cancer-free for at least the next six years, new research shows.

Aromasin, or exemestane, belongs to a newer class of breast cancer drugs known as aromatase inhibitors. They are being increasingly used as an alternative to the older generic drug tamoxifen for post-menopausal women with early breast cancer.

“We found that six years after changing treatment, women who got exemestane (Aromasin) were 18 percent more likely to remain disease free and were 14 percent less likely to die than those who stayed on tamoxifen,” Charles Coombes, head of oncology at Imperial College in London said on Tuesday.

The updated results, presented at the ECCO-ESMO cancer conference in Berlin, confirm that the benefits of switching from tamoxifen mid-way through a 5-year course of the drug do not seem to diminish over time, he said.

There are 1.29 million cases of breast cancer diagnosed worldwide every year. About 75 percent of these cancers are oestrogen-receptor positive, meaning they are susceptible to treatment with drugs like tamoxifen and Aromasin. (Reporting by Ben Hirschler, Editing by Lin Noueihed)