SPARC family proteins: matricellular modulators of cancer progression and therapeutic resistance

The SPARC (secreted protein acidic and rich in cysteine) family represents a unique class of matricellular proteins - including SPARC, SPARCL1, SPOCK1-3, SMOC1-2, and FSTL1 - that regulate extracellular matrix (ECM) dynamics, cell signaling, and tissue homoeostasis. In cancer, their expression is frequently dysregulated, through epigenetic mechanisms, microRNAs, and interactions within the tumor microenvironment (TME). Dysregulation of SPARC family members is most pronounced in aggressive malignancies with SPARC, SPARCL1, SPOCK1, and SPOCK2 most consistently altered. These proteins drive tumor progression through ECM remodeling, epithelial-mesenchymal transition (EMT), maintenance of cancer stemness, immune modulation, and drug resistance acquisition. Their functions are highly context-dependent, exerting either tumor-suppressive or oncogenic effects depending on tissue types and disease stage. While their secreted nature positions family members as promising serum or plasma biomarkers, challenges such as ECM protein undruggability, functional heterogeneity, and the absence of upstream regulators have so far precluded direct therapeutic targeting, with no agents advancing to clinical trials. Nonetheless, indirect strategies leveraging their biology show preclinical promise. This review synthesizes current knowledge on SPARC family structure, regulation, and context-specific functions in cancer-TME interactions, emphasizing their dual roles as modulators of progression and resistance. By integrating mechanistic insights with translational advances, we highlight the emerging utility of SPARC family proteins in precision oncology and underscore the need for deeper understanding to enable effective biomarker development and targeted therapeutic strategies.