TFRC and neoplasm: That said, should the radiotracer biodistribution be attributable to leukocyte accumulation in the tumor microenvironment rather than tumor autonomous TFRC expression, the observation that the leukocytes only measurably accumulated in 4 of 14 hepatic lesions is thought-provoking and could provide the foundation for hypothesis-driven research on the mechanism of leukocyte tropism to tumors.