In a pilot study by Beak and colleagues that included 10 patients with 18F-FDG PET positive NSCLC and 5 patients with breast cancer, immunohistochemical (IHC) analyses on these subjects’ pathology samples showed significant correlation between 18F-FSPG uptake and protein expression of both the SLC7A11 subunit of system xC- and the stem cell marker CD44. Here, CD44 is linked to breast cancer.