HSPA6 and neoplasm: As seen with other HSP proteins that are often increased in tumor settings without thermo-stimulation due to the proteotoxic stressful conditions that cancer cells face, including nutrient deprivation, the presence of free reactive oxygen species, hypoxia, acidosis, and high levels of mutant proteins 82, 83, the HSP70B promoter (HSP70B-NIS-MSC) showed increased basal activity within the tumor microenvironment in vivo as evidenced by gamma camera images in the 37 °C control group.