Exane BNP Paribas sees at least a 50% chance that US pharmaceutical giant Pfizer will return with a sweetened offer for UK rival AstraZeneca (AZN) following its failed takeover earlier this year.The bank said it expects another approach in November, when restrictions under takeover panel rules expire, as AZN is unlikely to invite Pfizer to talk."The manner in which the two companies approached the possible take-over last time was less than optimal for their respective shareholders, who were left frustrated by the failure of the parties to engage in meaningful discussions," said analyst David Finch."However, AZN's attractiveness for Pfizer is unchanged (and possibly enhanced by recent pipeline data)."Finch speculated that an offer of around £56-58 a share for AZN may be enough to get its board "to engage", following the rejected £55-a-share offer in May."November is only four months away, not that long to wait given the potential upside of around 30%."AZN shares were up 0.6% at 4,339.5p by 11:25.BC