Tumor Texture Analysis in PET: Where Do We Stand?

The coexistence of different tumor cells that show distinct morphologic and phenotypic features either within a tumor or between tumors defines tumor heterogeneity. The identification, characterization, understanding, and, possibly, treatment of tumor heterogeneity are key challenges in oncology and should help design effective therapeutic and monitoring strategies (1). Because biopsies probe only parts of the tumors, they do not necessarily reflect tumor heterogeneity (2). Additional techniques are needed, among which imaging is an appealing approach to comprehensively detect, depict, and quantify local variations in tumor morphology and function. Several hundred published articles have investigated the beneficial information that can be extracted from the analysis of tumor heterogeneity using imaging since the beginning of the nineties, mostly involving MR and ultrasonography (.70% of the articles) (3), with a significant increase in publications since 2008. The interest in exploring tumor heterogeneity using PET dates back to 2009 (4) and is conceptually quite appealing given that PET reflects the biology of the tumor. Yet, a synthetic synopsis of the published results and subsequent