Further investigation revealed that FAP5-CAR-transduced T cells might target FAP-positive multipotent bone marrow stromal cells, which could explain the observed bone marrow toxicity.328 Similarly, Roberts et al. reported that the depletion of FAP+ stromal cells results in muscle wasting and altered hematopoiesis.329 Collectively, these observations implicate fibroblasts as critical regulators of muscle homeostasis, and the absence of fibroblasts in skeletal muscle can contribute to muscle atrophy in cancer cachexia. Here, FAP is linked to cancer.