FOLR1 and breast carcinoma: Some studies have investigated resistance patterns of FRα-CAR T cells by analyzing markers such as levels of carcinoma-associated fibroblasts (CAFs), which regulate cancer progression through IL-6, which in turn can promote PD-L1 expression, which is linked to FRα-CAR T resistance/ineffective CAR T killing in patients with breast cancer receiving doxorubicin [40].