* Doctors, payers see biosimilars as way to cut cancer costs
* Roche faces first biosimilar in EU, others coming
* 40 pct sales fall forecast for three Roche drugs by 2021
By Ben Hirschler
LONDON, Sept 18 (Reuters) - The long-heralded threat of cut-price competition to its top-selling biological cancer medicines is finally becoming a reality for Roche, the world's biggest maker of oncology treatments.
Last Friday's green light for a copy of its breast cancer drug Herceptin heralds the arrival of the second so-called cancer biosimilar in Europe this year, following the launch six months ago of copies of MabThera/Rituxan for blood cancers.
Across the Atlantic, U.S. regulators have approved a biosimilar version of Avastin for a range of cancers, although outstanding patents mean it is likely to be a couple of years before cheap copies of this product hit the market.
The pace of sales erosion due to such biosimilars is expected to be gradual yet relentless.
Rituxan, Herceptin and Avastin together had 2016 revenue of 20.9 billion Swiss francs ($21.8 billion) - equal to more than half Roche's pharmaceuticals business - but their combined sales are expected to fall more than 40 percent by 2022, according to consensus analyst forecasts compiled by Thomson Reuters.
The Swiss drugmaker needs to run fast to offset that big hit by making a success of its new cancer drugs, such as Perjeta, Gazyva and Tecentriq.
Biosimilars - medicines that are highly similar to the original drug, making them safe and effective to use - offer a route to more affordable cancer care at a time when the price of modern therapies to fight tumours is going through the roof.
Leading cancer doctors meeting at this month's European Society for Medical Oncology (ESMO) congress made clear that optimising use of cheaper copies of such antibody medicines, which are given as injections or infusions, was now a priority.
"Once they have gone through all the proper processes of registration and approval by health authorities, the use of biosimilars should be encouraged because they are an important way to deliver sustainable cancer care," ESMO President Fortunato Ciardiello told Reuters.
So far, Roche has seen little impact from the arrival of biosimilar MabThera in Europe, a company spokeswoman said. The first impact from Herceptin biosimilars is expected by the end of this year.
But experts believe the pressure will grow steadily.
By 2021, European healthcare systems are likely to enjoy annual savings of close to 2 billion euros ($2.4 billion) due to biosimilar competition to Roche's three giant oncology medicines, according to Murray Aitken, head of the QuintilesIMS Institute, an authority on prescription drug sales trends.
That compares to an estimated 300 million euros of savings from Rituxan biosimilars alone in 2017.
The potential of biosimilars is a lure for rival manufacturers, including established generic drug suppliers such as Mylan and Novartis's Sandoz division, as well as South Korean specialists Celltrion and Samsung Bioepis.
It is also a significant opportunity for cash-strapped healthcare providers across Europe.
NHS England head Simon Stevens highlighted the opportunity to save hundreds of millions of pounds by using biosimilars in a speech last week, adding their introduction had the dual advantage of also driving down the cost of the original drugs.
Stevens noted the first biosimilar antibody drug for rheumatoid arthritis and gastrointestinal disorders, infliximab, had driven down cost of treatment by nearly two-thirds to 6.84 pounds ($9.26) a day from 16.80 pounds. ($1 = 0.8372 euros) ($1 = 0.7386 pounds) ($1 = 0.9594 Swiss francs) (Additional reporting by John Miller in Zurich; editing by Susan Thomas)