Wong et al. reported two patients with interstitial pneumonia (IP) associated with collagen diseases (dermatomyositis (DM) and polymyositis (PM)) who showed elevated levels of CA15-3 but did not have breast cancer.1 The authors did not measure the level of KL-6, because measurement of this parameter was available only in Japan in 2005. We examined the relationship between the serum levels of KL-6 (Picolumi® KL-6, Sanko Junyaku, Tokyo, Japan) and those of CA15-3 (Lumipulse® CA15-3, Fujirebio, Tokyo, Japan) in 20 female patients with IP associated with collagen diseases (rheumatoid arthritis (seven cases), PM (four), systemic sclerosis (three), Sjögren syndrome (three), mixed connective tissue disease (two) and DM (one)). The normal range of KL-6 and CA15-3 are <500 U/mL and ≤27.0 U/mL, respectively. As shown in Figure 1, there was a significantly positive correlation between the levels of KL-6 and those of CA15-3 (r = 0.74, P < 0.001). In five cases, the levels of CA15-3 were above the normal range, but none had a diagnosis of breast cancer by mammography. Relationship between the serum levels of KL-6 and those of CA15-3 in 20 patients with interstitial pneumonia associated with collagen diseases. A significantly positive correlation was noted by a linear regression analysis (r = 0.74, P < 0.001). KL-6 was initially identified as a tumour marker for adenocarcinoma of the lung. When the lung interstitium is injured, KL-6, which is mainly expressed on the surface of alveolar type II cells in the lung, fluxes into the blood circulation following an increase in the permeability of the damaged air–blood barrier.2 High serum levels of KL-6 are detected not only in patients with adenocarcinoma of the lung, pancreas or breast, but also in patients with IP including idiopathic pulmonary fibrosis, hypersensitivity pneumonitis, radiation pneumonitis, pulmonary sarcoidosis, collagen diseases-associated IP and methotrexate-induced IP.2 KL-6 is now used in Japan as a serum marker for the purpose of making a diagnosis of IP, and monitoring its severity and therapeutic efficacy.3 CA15-3 is a marker for the early detection of a recurrence of breast cancer and for assessing the efficacy of treatment for metastatic breast cancer.4 This antigen is recognized by two monoclonal antibodies, namely 115D8 and DF3, which react against the human milk-fat globule membrane and breast cancer cells, respectively.5, 6 High serum levels of CA15-3 are detected not only in patients with breast cancer, but also in patients with adenocarcinoma of the lung, pancreas, kidney, ovary, uterus and colon.7 Both epitopes of KL-6 and CA15-3 exist in the different positions of Mucin-1 (MUC-1) expressed on the surface of various epithelial cells.8 MUC-1, classified as one of the mucin family, is a high-molecular-weight glycoprotein rich in O-glycosylated serine and threonine residues. The upregulated expression of MUC-1 has been noted in breast and lung adenocarcinomas.9 This might be the reason why the serum levels of KL-6 positively correlated with those of CA15-3. Ogawa et al. reported that the sensitivity of KL-6 was higher than that of CA15-3 in patients with relapsed breast cancer.10 According to the results of this study, the following points are important: (i) the levels of CA15-3 may increase not only in patients with adenocarcinoma including breast cancer but also those with IP; (ii) CA15-3 might thus be usable as a parameter of IP in patients without adenocarcinoma, including breast cancer.
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