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Western blotting of serum sialyl Lewis X-i antigen could become a diagnostic tool after research in Japan has shown that it helps to separate lung adenocarcinoma from idiopathic pulmonary fibrosis (IPF). High serum concentrations of the antigen are used as a marker for lung adenocarcinoma, but these also occur in IPF, bronchiectasis, and diffuse panbronchiolitis, without cancer. Furthermore, patients with IPF have increased risk of developing cancer, so those with high serum antigen have invasive and expensive confirmatory tests for cancer.

Working from the premise that glycoprotein antigens—like Lewis X-i—have variable core proteins, Satoh et al evaluated Western blotting as a method to differentiate between the major disease types. They compared the molecular bands resulting from serum samples of 23 patients with confirmed lung adenocarcinoma or other lung disease—IPF, bronchiolitis, and diffuse panbronchiolitis—all of whom had sialyl Lewis X-i antigen >50 U/ml. Excluded from the cancer group were patients with infection or fibrotic lung changes and from the IPF group any who developed cancer over three years' follow up.

The banding pattern was essentially the same in patients with the same diagnosis. A signature band of MW 120/130 kD occurred in 13 of 14 patients with carcinoma , with three further bands <97.4 kD in two of them, and 2/3 bands <97.4 kD occurred in five of six patients with IPF. The test's sensitivity; specificity; and positive and negative likelihood ratios were favourable, so provided the results are replicated in a larger study, this is an important advance.

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