Fibroblast activation protein, a potential diagnostic and therapeutic target for cancer.

Abstract

To the Editor, Fibroblast activation protein (FAP) has long been known to be expressed in the stroma of cancer. Park et al [1] suggested that the specific and consistent expression of FAP could play an important role in the formation, remodeling, or maintenance of tumors. However, the relationship between FAP expression and tumors is still unclear. Recently, we read with great interest the article entitled “Fibroblast activation protein expression by stromal cells and tumor-associated macrophages in human breast cancer,” which indicated that the expression of FAP was abundantly shown in the stroma across all breast cancer subtypes and demonstrated that the expression of FAP could be regulated by human breast tumor–associated macrophages [2]. These findings suggest that FAP might play a crucial role in the pathogenesis of breast cancer and that FAP also might be a potential targetable molecule in the treatment of breast cancer. Interestingly, Cai et al [3] also reported that the FAP, which was targeted by short hairpin RNA, could inhibit tumor growth and improve tumor microenvironment in a mouse model. They showed that short hairpin RNA targeting of FAP in murine breast cancer reduced the expression of FAP and inhibited tumor growth. Moreover, they suggested that targeted FAP might represent a supplementary therapy for breast cancer [3]. Furthermore, Yuan et al [4] found that, in osteosarcoma, the most common primary solid tumor of the bone, the messenger RNA and protein expression of FAP both were higher than in corresponding noncancerous bone tissues. In addition, they demonstrated that FAP could be adopted as a candidate biomarker in osteosarcoma. Thus, they suggested that FAP might play a role in diagnosis and treatment of tumor development and progression in osteosarcoma [4]. Another recent study, by Schuberth et al [5], showed that FAP was expressed in all subtypes of malignant pleural mesothelioma, a rare solid organ tumor, and that FAP-specific redirected T cells could be used for the treatment of patients with malignant pleural mesothelioma. In summary, these aforementioned studies demonstrate that the expression of FAP is verified in many tumor tissues and suggest a potential role for FAP in cancer diagnosis and treatment. However, further studies need to comprehensively extend the role of FAP in cancer.