0844 GMT - AstraZeneca is hedging against a key threat to its antibody drug conjugate portfolio through its collaboration with Summit Therapeutics, Citi analysts say in a research note. The agreement has limited immediate impact, but it is a sensible move by the U.K. drugmaker in case medicines like Summit's ivonescimab--known as PD-1/VEGF--become an alternative backbone therapy to existing treatments called PD-1 and PD-L1, the analysts say. AstraZeneca is testing its Datroway antibody drug conjugate in combination with its PD-L1 medicine Imfinzi for lung cancer in a late-stage clinical trial. Moreover, AstraZeneca's stake in Summit gives it exposure to PD-1/VEGF in the event the drug class takes off, the analysts add. AstraZeneca shares rise 0.1%.