Objective: Despite the use of surgical and chemoradiation therapies, head and neck squamous cell carcinoma (HNSCC) still has a poor prognosis. Immune checkpoint inhibitors have been shown to prolong life expectancy but have limited efficacy. Glycoprotein nonmetastatic melanoma protein B (GPNMB) has received significant attention in breast cancer treatment, in which it has been associated with cancer stem cells (CSCs) and epithelial-mesenchymal transition (EMT); however, the function of GPNMB in HNSCC is completely unknown. This study aimed to clarify the characteristics of GPNMB-positive cells in vitro and their association with the prognosis by immunostaining clinical specimens.Methods: We examined the sphere formation, invasion, and migration ability of GPNMB-positive cells in four HNSCC cell lines in vitro. We also immunostained biopsy specimens with GPNMB from 174 patients with HNSCC diagnosed, treated, and followed-up in our institution to evaluate overall survival and progression-free survival.Results: GPNMB-positive cells showed enhanced sphere formation, invasion, and migration, suggesting that they could have CSC characteristics and the ability to induce EMT, as reported for breast cancer. Clinical specimens showed that overall survival was 39.4% and 57.8% (p = 0.045) and that progression-free survival was 27.6% and 51.6% (p = 0.013) for the high-expression and the low-expression groups, respectively, indicating poor prognosis for the high GPNMB group. The high GPNMB group was also more resistant to chemoradiation and bioradiotherapy. GPNMB was more highly expressed in metastatic lymph nodes than in the primary tumor.Conclusion: GPNMB-positive cells might have CSC characteristics and induce EMT. Detailed functional analyses of GPNMB in HNSCC and the establishment of therapies targeting GPNMB will lead to improved prognoses.

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Head and neck squamous cell carcinoma (HNSCC) has been identified as the sixth most common disease in the world, and its prognosis remains poor. The basic treatment of HNSCC includes a combination of chemoradiation and surgery. With the advent of immune checkpoint inhibitors, the prognosis has improved; however, the efficacy of checkpoint inhibitors is limited. L-type amino acid transporter 1 (LAT1), an amino acid transporter, is highly expressed in a cancer-specific manner. However, to the best of our knowledge, LAT1 expression in HNSCC has not been determined. Therefore, the present study aimed to examine the role of LAT1 expression in HNSCC. A total of three HNSCC cell lines (Sa3, HSC2 and HSC4) were used to investigate the characteristics of LAT1-positive cells, including their ability to form spheroids, and their invasion and migration. The present study also examined LAT1 by immunostaining of biopsy specimens from 174 patients diagnosed, treated and followed-up at Akita University (Akita, Japan) between January 2010 and December 2019, and overall survival, progression-free survival and multivariate analyses were performed. The results demonstrated that LAT1-positive cells in HNSCC were an independent prognostic factor for overall survival and progression-free survival, and were resistant to chemoradiation. Therefore, JPH203, a LAT1 inhibitor, may be effective in treating chemoradiotherapy-resistant HNSCC and may improve the prognosis of patients with HNSCC.

CD98 is a marker of cancer stem cells, and it regulates radiosensitivity in head and neck squamous cell carcinoma (HNSCC). The current study aimed to investigate whether CD98 can be used as a prognostic factor and marker of radioresistance. CD98 immunostaining was performed using biopsy specimens collected from patients diagnosed with HNSCC. The average period of postoperative monitoring was 31.6 months. The treatment options were radiation therapy with either cisplatin or cetuximab, and surgery. The participants were divided into groups of low and high fluorescence intensity. CD98 was an independent prognostic factor of radioresistance. In total, 103 patients were treated with chemoradiotherapy or bioradiotherapy. The overall survival rates of patients receiving chemoradiotherapy or bioradiotherapy were 69.2% in the low group and 36.2% in the high group. The progression-free survival rates were 60.0% and 24.6%, respectively. CD98 expression was considered an independent prognostic factor of overall survival and progression-free survival. In total, 99 patients underwent surgical treatment. The surgery group did not differ according to CD98 expression. Via CD98 immunostaining, sensitivity to radiotherapy can be determined in advance. In HNSCC, knowledge about sensitivity to radiotherapy can significantly improve prognosis.