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* Roche set to compete with established GSK combination
* Similar results with BRAF/MEK cocktails in melanoma
* Different side effects may determine choice of regimen
* Shares in Roche's biotech partner Exelixis jump 20 pct (Adds Exelixis share price jump, more on treatment debate)
By Ben Hirschler
MADRID, Sept 29 (Reuters) - Rival two-pill combinations formelanoma from Roche and GlaxoSmithKline hadsimilarly good results in separate clinical trials, leavingdoctors with little to choose between the two skin cancercourses.
The latest findings will fuel a wider debate about theoptimal treatment of melanoma as a new generation ofimmune-stimulating injections offers an alternative way to fightthe deadliest form of skin cancer.
Roche's combination -- which includes a drug discovered byExelixis, whose shares jumped some 20 percent inpremarket trade on the study news -- is not yet available. GSKis already marketing its combined treatment.
GSK, however, plans to sell its melanoma drugs and otheroncology products to Novartis under a deal announcedin April.
Both combinations are designed to block two proteins, knownas BRAF and MEK, that are associated with tumour growth and areimplicated in about half of all cases of metastatic melanoma,where the disease has spread to other parts of the body.
In the 495-patient study sponsored by Roche, patients giventhe company's Zelboraf drug and the experimental compound cobimetinib lived a median 9.9 months before their diseaseworsened, against 6.2 months when they took Zelboraf alone.
GSK's trial, involving 704 patients, showed its combinationof the drugs Tafinlar and Mekinist increased progression-freesurvival by 11.4 months versus 7.3 months for patients onZelboraf.
In both cases, patients were selected for inclusion in the studies after they had been shown to have a genetic mutationmaking them sensitive to such treatments.
The findings from the two studies were presented on Mondayat the European Society of Medical Oncology annual congress inMadrid. The Roche study was also published online in the NewEngland Journal of Medicine (NEJM).
Reinhard Dummer of the University of Zurich Hospital, whowas not involved in the tests, said the results were verysimilar and the clear improvement seen in both cases provided"convincing evidence" that such combination therapy should beused routinely.
"There is hardly any space for monotherapy now," he said.
SIDE EFFECTS
Given the almost identical clinical outcomes, choosingbetween the two regimens will likely come down to the slightlydifferent side effect profiles of the two BRAF inhibitors usedin the combinations, Dummer said.
GSK's Tafinlar is linked to a higher rate of fever, whileRoche's Zelboraf is linked to photosensitivity, which can causesevere sunburn. Dummer said this could make it less suitable forpatients living in sunny climates.
Roche plans to submit its combination to regulators aroundthe world for approval.
Cobimetinib, the second experimental pill in the Rochecombination, is being developed with U.S. biotech companyExelixis.
All these pills are examples of targeted cancer drugs,designed to turn off very specific molecular pathways associatedwith disease. This approach can have dramatic effects in theshort term but tumour cells tend to go on to develop resistance.
While combining two drugs extends the response, oncologistsare also looking at ways to generate a much more durable effect,with attention now focusing on immunotherapy treatments that canoffer longer-term benefits.
"Evidence suggests that these agents can lead to durabletumour responses in patients with metastatic melanoma, albeitwith lower response rates than have been observed with BRAF andMEK inhibition," researchers on the Roche study wrote in theNEJM.
Working out when to use the BRAF/MEK inhibitors and when touse immunotherapy is the next question oncologists aim to tacklewith a new programme of clinical testing.
More than 230,000 people worldwide are diagnosed withmelanoma each year, according to the World Health Organisation.If the disease is caught early, it can be cured -- but mostpeople with advanced melanoma have a poor prognosis. (Editing by David Clarke)
