Stent dysfunction was caused by tumor ingrowth , tumor overgrowth , and sludge formation in 0 ( 0 % ) , 3 ( 5 % ) , and 11 ( 18 % ) patients in the covered SEMSs group , and in 15 ( 25 % ) , 2 ( 3 % ) , and 6 ( 10 % ) patients in the uncovered SEMSs group , respectively .
