Study of Pomalidomide Combination with Rituximab and Anti-PD-1 Antibody （PPR） in Third or Later Line Therapy of DLBCL

"All patients will receive the PPR regimen (a total of 4-6 cycles, 28 days for each cycle):~* pomalidomide: 4 mg, orally, once daily from Day 1 to Day 21.~* Rituximab: 375 mg/m², administered on Day 1.~* PD-1: 200 mg, administered on Days 1."