Patients aged 18 years or older with advanced pancreatic cancer were randomly assigned ( 1:1 ) , via a permutated computer-generated block allocation scheme ( block size of six ) to receive intravenous gemcitabine ( 1000 mg/m ( 2 ) ) on days 1 , 8 , and 15 every 4 weeks and oral erlotinib ( 100mg ) once daily in combination with either oral metformin or placebo twice daily .