SPARC and cancer: SPARC, which is considered to be solely produced by cancer associated fibroblasts in the tumor stroma, is suggested to regulate tumor cell growth and metastasis.34, 35 In a study by Witkiewicz et al, SPARC expression was correlated to tumor recurrence in ductal carcinoma in situ (DCIS) of the breast.36 Moreover, Chang et al show that in HNSCC a higher SPARC expression correlated to a higher tumor grade,37 but the prognostic role of SPARC expression is however still inconsistent within and between cancer types.35