Soluble MICB Serum Levels Correlate with Disease Stage and Survival Rate in Patients with Oral Squamous Cell Carcinoma

Background: Expression of ligands of natural killer group 2D (NKG2D) immunoreceptors, such as major histocompatibility complex class I-related chain A/B (MICA/B), has been proposed to play an important role in tumour immunosurveillance. Soluble forms of MICA/B are increased in sera of cancer patients and are postulated to impair antitumour immune response by downregulating expression of NKG2D immunoreceptors. Serum levels of soluble MICA have been shown to be of diagnostic significance in malignant diseases. Aims: The potential of soluble MICB (sMICB) as a marker for oral squamous cell carcinoma (OSCC) was investigated. Results: sMICB levels did not differ significantly from those in normal control individuals. However, the findings indicate that sMICB levels are significantly increased in stage IV OSCC and high sMICB levels are significantly associated with decreased survival rates in patients. Oral squamous cell carcinoma (OSCC) is a solid tumour of epithelial origin. It is the sixth most common cancer globally, although its incidence varies dramatically with location. The relative frequency of OSCC ranges from less than 1% to over 40% amongst all malignancies (1). Approximately 6,000 cases of OSCC are diagnosed annually in Japan, and it is related to tobacco and alcohol consumption (2). Despite aggressive and often mutilating therapeutic regimens, overall survival in OSCC has remained largely unchanged over the past 20 years. Improvement in long-term survival rate of patients with OSCC requires identification of prognostic markers that can differentiate patients with a high risk for local recurrence and lymph node metastasis. The human leukocyte antigen (HLA) system plays an important role in the cellular immune response to viral and tumour antigens (3). The HLA region is located on chromosome 6p21.3 and encompasses a 4 Mb segment that has evolved through repeated gene duplication and conversion events (4). The major histocompatibility complex (MHC) class I