Blood protein may improve lung cancer diagnosis and treatment
MedWire News: Patients with lung cancer have significantly higher levels of serum amyloid A (SAA) protein than healthy controls, indicating that the protein may serve as a useful marker of lung adenocarcinoma, say researchers.
SAA, an acute phase protein, is also implicated in lung cancer metastasis and may therefore represent a therapeutic target for the inhibition of disease progression, they add.
Je-Yoel Cho (Kyungpook National University, Daegu, Korea) and colleagues explain that early detection of lung cancer could significantly improve the currently poor survival rates associated with the disease, but X-ray and computed tomography screening methods are limited by poor specificity and high cost.
They therefore screened serum samples from patients with lung adenocarcinoma and healthy controls to search for differentially expressed proteins that could be used as lung cancer biomarkers.
Liquid chromatography-mass spectometry analysis showed that SAA was present in the pooled sera of five lung cancer patients but not in that of five healthy controls. Western blot analysis confirmed this finding, with SAA detected in 42 (52.5%) of 80 serum or plasma samples from adenocarcinoma patients compared with only one (1.7%) of 60 samples from healthy controls.
The researchers report that patients with lung adenocarcinoma (n=170) had serum/plasma SAA levels that were approximately 14 times higher than those of healthy controls (n=180), at 190.5 vs 13.9 μg/ml.
Moreover, SAA level did not vary significantly with cancer stage (I-IV). This, says the team, indicates that the protein may have diagnostic usefulness in both early- and late-stage cancer.
To test the specificity of SAA to lung cancer, the researchers measured SAA levels in samples from patients with tuberculosis (TB), idiopathic pulmonary fibrosis, bronchial asthma, stomach cancer, and breast cancer.
They found that SAA levels were significantly lower in samples from patients with each of these conditions compared with those from patients with adenocarinoma, with the exception of TB where this difference did not quite reach significance.
Further in vitro experiments showed that SAA stimulated the expression of matrix metalloproteinase-9 by macrophages, an occurrence which the researchers believe promotes metastasis. In addition, overexpression of SAA increased the metastatic characteristics of Lewis lung carcinoma (LLC) cells in vivo.
Writing in the Journal of Proteome Research, the researchers say that the higher levels of SAA present in serum/plasma samples from lung cancer patients can be explained, in part, by direct secretion of SAA from lung cancer cells.
They conclude that raised SAA levels may act as an additional diagnostic marker for lung cancer and could also provide clues for future lung cancer treatment.
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By Laura Dean