Introduction. Uveal melanoma (UM) is an intraocular tumor that leads to metastatic disease in approximately 50% of afflicted patients. There is no efficacious treatment for metastatic disease in this cancer. Identification of markers that can offer prognostic and therapeutic value is a major focus in this field at present. KAI1 is a metastasis suppressor gene that has been reported to play a role in various human malignancies, although it has not previously been evaluated in UM. Purpose. To investigate the expression of KAI1 in UM and its potential value as a prognostic marker. Materials and Methods. 18 cases of human primary UM were collected and immunostained for KAI1 expression. A pathologist evaluated staining intensity and distribution semiquantitatively. Each case was categorized as group 1 (low staining) or group 2 (high staining). Results. In group 2, two of the 12 cases presented with metastasis. Conversely, in group 1, five out of 6 cases had metastasis. The mean follow-up of patients who did not develop metastasis was 81.81 months (median: 75 months) versus 42.14 months (median: 44 months) for patients with metastasis. Conclusions. KAI1 is a promising candidate marker that may offer prognostic value in UM; it may also represent a therapeutic target in metastatic disease. 1. Introduction Uveal melanoma (UM) is the most common primary intraocular malignant tumor in adults, as well as the most common noncutaneous melanoma. This tumor primarily affects Caucasians and has an incidence of approximately 6 cases per million [1]. Metastasis—the leading cause of death in UM patients—can be present at the same time as the diagnosis of the primary tumor or several years thereafter [2, 3]. Tumor metastasis occurs via hematogenous dissemination, with the liver being the most common organ affected, followed by lung and bone [4, 5]. Metastasis suppressor genes (MSGs) are known to play a role in numerous cancers. They are of particular interest to researchers given that they can be implicated in various steps of the metastatic cascade and thus may have therapeutic value. Expression of MSGs is frequently reduced in highly metastatic tumor cells [6]. The MSG KAI1 has previously been shown to interfere with multiple steps of the metastatic cascade, including proliferation, invasion, and migration, making it an attractive marker to evaluate in UM and other cancers [7, 8]. Multiple studies have demonstrated that the expression of KAI1 in some primary tumor types is inversely correlated with formation of metastasis [9]. The aim of this study was to investigate the
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