In solid tumor preclinical experiments, intraperitoneal (i.p.) CAR-T administration produced stronger antitumor effects than standard intravenous (i.v.) delivery. The study reported increased CAR-T persistence both systemically and within the tumor, with improved endpoint measures of tumor control and altered exhaustion-associated receptor expression. The work also used PET-CT tracking with radiolabeled CAR-T cells to compare early biodistribution, supporting the conclusion that local delivery routes can overcome delivery barriers that limit CAR-T effectiveness in solid tumors.