Diffuse Expression of RNA-Binding Protein IMP3 Predicts High-Stage Lymph Node Metastasis and Poor Prognosis in Colorectal Adenocarcinoma

IMP3 (insulinlike growth factor II mRNA-binding protein 3) is a newly identified oncofetal RNA-binding protein that is involved in cell growth and cell migration during the early stages of embryogenesis. This study sought to elucidate its role in tumor progression and prognosis of colorectal adenocarcinoma (CRA). IMP3 expression in 186 surgically resected unifocal primary CRAs was analyzed by immunohistochemistry. The proportions of tumor cells positive for IMP3 were scored into diffuse (a parts per thousand yen50%), focal or heterogeneous (10-50%), and trace (< 10%), and the expression levels were correlated with clinicopathologic features and patient survival. Cytoplasmic immunoreactivity for IMP3 was diffuse in 66 (35%), focal or heterogeneous in 38 (21%), and trace in 34 (18%) samples. No staining was seen in the adjacent nontumorous tissue. Diffuse IMP3 expression correlated with large tumor (> 3 cm, P = .0452), high-stage tumor (IIIa-IV, P = .0417), lymph node metastasis (P = .0232), high lymph node ratio (LNR a parts per thousand yen .7, P = .0016), and lower 5-year survival (P = .0012). Further analysis showed that patients with high-stage CRA and diffuse IMP3 expression had the worst survival rate (P < .0001)-far worse than those without diffuse IMP3 expression (P = .0038). Moreover, multivariant analysis showed diffuse IMP3 expression, serosal invasion, LNR, tumor stage, and adjuvant chemotherapy were independent prognostic factors in CRA. Diffuse IMP3 protein expression correlates with invasion and aggressiveness during cancer growth and metastasis, and it is an important prognostic factor of CRAs.