Suzuki J, et al. - Via involving 90 patients who had the first pulmonary metastasectomy for metastatic lung cancers from the colon and rectum (MLCR) with a tumor diameter ≦ 3.0 cm and without chemotherapy, clinicopathological factors associated with the amount of necrosis in MLCR have been elucidated. The connection between necrosis percentage (NP) and clinicopathological factors have been analyzed. In addition, tissues were analyzed by immunohistochemical staining using carbonic anhydrase IX (CAIX), CD34 antibodies, and Ki-67 antibodies, to determine whether NP was affected by tissue hypoxia, vascularization, or tumor cell proliferation. Although NP was not linked to the tumor area, in patients with a positive history of smoking it was significantly higher. There was no correlation between other clinicopathological factors and NP. Immunohistochemical analysis revealed that NP was not significantly associated with CA IX expression on tumor cells, CD34 micro-vessel density, CD34 micro-vessel area, and Ki-67 index. In the pulmonary metastasis, NP was not associated with NP at the primary site. Tumor size, tissue hypoxia, vascularization, or proliferation of tumor cells did not determine NP. A positive correlation between NP and smoking history suggests a unique lung microenvironment in smokers that increases the likelihood of MLCR necrosis.