Pharmaceutical giants AstraZeneca and Merck said Thursday they had agreed a multi-billion-dollar deal to jointly develop key cancer drugs.   "The strategic collaboration is expected to further increase the number of treatment options available to patients," British company AstraZeneca and its US peer said in a statement.    Merck will pay AstraZeneca up to $8.5 billion (7.2 billion euros) under the deal struck to develop and commercialise the drugs. source:AFP