PRF1 and neoplasm: The CD27+ CD11b− immature NK subset in the liver was found to protect against liver metastasis, but not pulmonary metastasis, through a NK cell perforin-dependent cytotoxic mechanism, while the (CD27− CD11b+) mature NK cell subset found in the lung whilst unable to efficiently prevent metastasis formation, yet controlled tumor load (fewer pulmonary nodules).