Astrazenca was leading the pharmaceuticals sector higher on Thursday on the back of speculation that US drug giant Pfizer could return with a fresh offer in the coming days.The reports lifted others in the sector higher in afternoon trading with peers such as Glaxosmithkline, Hikma and BTG making decent gains.Pfizer, which walked away from its attempted £71bn takeover in May, will not be able to initiate talks with the British-Swedish group until 26 November because of the six-month two-stage 'cooling-off' period under UK Takeover Panel rules.However, Astrazeneca could invite the US company back to the table from 26 August.Astrazeneca was resolute in its defence against a bid earlier in the year, reassuring investors that it is better off as an independent company with attractive growth prospects and a decent pipeline. However, it is thought that heightened pressure from shareholders who had wanted the original deal to go through could prompt management to revise its stance.Astrazeneca's shares were up 2.4% at 4,386.5p by 14:29.With Pfizer still on the lookout for deals - in an effort to cut its tax bill through inversion and gain a new drug pipeline - reports suggest that it is considering other targets such as Ireland's Actavis or even Astrazeneca's bigger rival Glaxosmithkline.However, Astrazeneca is widely seen as the more attractive fit.Top performing sectors so far todayConstruction & Materials 3,936.21 +1.66%Pharmaceuticals & Biotechnology 12,857.84 +1.32%Health Care Equipment & Services 5,943.56 +0.99%Aerospace and Defence 4,907.25 +0.81%Forestry & Paper 10,900.61 +0.80%Bottom performing sectors so far todayElectricity 9,590.35 -0.49%Industrial Transportation 2,805.96 -0.39%Media 6,168.80 -0.19%Mining 17,847.95 -0.19%Mobile Telecommunications 4,524.77 -0.18%BC