* Shares slip by 1.2 percent
* Roche says sales will grow despite competition from copies
ZURICH, Sept 11 (Reuters) - Roche shares fell in early trading on Monday after trial failures added to the Swiss drugmaker's challenge of replacing patent-expired medicines with lucrative new drugs.
Its skin cancer treatment Zelboraf flopped, the company said on Monday, while similar drugs from Novartis achieved their goals.
Additionally, analysts now doubt prospects for Roche's eye drug lampalizumab after it failed a separate trial, jeopardising more than $2 billion in potential annual sales.
Roche has been counting on new drugs to bolster its business as rivals produce cheaper biosimilar copies of its biggest sellers -- the $20 billion-a-year trio of cancer drugs Herceptin, Avastin and Rituxan.
But the recent flops, coupled with disappointing results this year on its immunotherapy Tecentriq and its Herceptin-Perjeta combination, underscore the challenge Roche faces.
"In a best case, lampalizumab could have been a significant driver of Roche earnings growth over the next five years," Kepler Cheuvreux analyst David Evans wrote in a note.
"Virtually removing it from models will put more pressure on Roche sales, and on Roches attempts to keep margins even flat, as biosimilars start to take hold."
Roche shares were down 1.2 percent at 241.60 Swiss francs in early trade while Switzerland's benchmark SMI rose.
Goldman Sachs analysts cut their price target on the stock to 325 francs from 335 francs.
Already, numerous versions of Roche's Rituxan, also called MabThera, have been approved in Europe and are being reviewed in the United States.
Copies of Herceptin and Avastin are hot on their heels.
Despite trial mis-steps, Roche has enjoyed several approval wins. Among top new drugs, Ocrevus is making headway in winning multiple sclerosis patients, generating 192 million Swiss francs ($201.94 million) in the first half.
Moreover, the FDA is expected by mid-February to make a decision on haemophilia medicine ACE910, which is expected eventually to add billions to Roche's bottom line.
Roche, which upgraded its sales guidance for 2017 in July, continues to expect its new drugs -- Tecentriq, Gazyva and Perjeta, at the top of the list -- to drive sales growth despite erosion because of biosimilars.
Jefferies analyst Jeffrey Holford was sanguine about the trial failures, saying they will not derail Roche's sales growth.
"Other new product development and launches, such as Ocrevus, Tecentriq and ACE910, look set to drive continued growth for the company despite approaching biosimilar headwinds," he said. ($1 = 0.9508 Swiss francs) (Reporting by John Miller; Editing by David Goodman)