Although correlations between Ki67 proliferation marker expression level and diffuse optically measured physiological parameters have not been reported, several positron emission tomography (PET) studies have found correlation between Ki67 cancer proliferation level and fluorodeoxyglucose (FDG) metabolism [40–42], but a different study reported no correlation between Ki67 and 18F-FDG uptake, and a marginal correlation between Ki67 expression level and tumor-to-background ratio of the uptake of the hypoxia-avid compound 18F-labeled fluoromisonidazole (18F-FMISO) [43]. The gene discussed is MKI67; the disease is neoplasm.