MicroRNA-375 Suppresses Extracellular Matrix Degradation and Invadopodial Activity in Head and Neck Squamous Cell Carcinoma

Overexpression of POFUT1 promotes malignant phenotype and mediates perineural invasion in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is one of the most aggressive neoplasms, which requires more effective prevention and treatment modalities. Previous studies found that protein O-fucosyltransferase 1 (POFUT1) upregulation promotes carcinogenesis, although the potential roles, underlying molecular mechanisms, and biological implications of POFUT1 in HNSCC were not investigated. In this study, in silico analyses referred POFUT1 as a potential oncogene in HNSCC. Further analysis of tumor and normal tissue samples as well as HNSCC cells with quantitative real-time polymerase chain reaction, Western blot analysis, and immunohistochemistry showed significant overexpression of POFUT1 in HNSCC clinical tumor tissue specimens and cell lines compared to corresponding controls. In vitro investigations revealed that overexpression of POFUT1 promoted phenotypes associated with cancer aggressiveness and its knockdown in HNSCC cells suppressed those phenotypes. Further xenograft experiments demonstrated that POFUT1 is an oncogene in vivo for HNSCC. Immunohistochemical analysis with human clinical samples and cancer cell-dorsal root ganglion ex-vivo coculture model showed that deregulation of POFUT1 is involved in the perineural invasion of HNSCC cells. These results suggest POFUT1 expression as a potential prognostic marker for patients with head and neck cancer and highlight its potential as a target for HNSCC therapy, although more molecular clues are needed to better define the functions of POFUT1 related to HNSCC carcinogenesis.

Picrasidine J, a Dimeric β-Carboline-Type Alkaloid from Picrasma quassioides, Inhibits Metastasis of Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) are associated with recurrence, distant metastasis, and poor overall survival. This highlights the need for identifying potential therapeutics with minimal side-effects. The present study was designed to investigate the anticancer effects of picrasidine J, a dimeric β-carboline-type alkaloid isolated from the southern Asian plant Picrasma quassioides. The results showed that picrasidine J significantly inhibits HNSCC cell motility, migration, and invasion. Specifically, picrasidine J inhibited the EMT process by upregulating E-cadherin and ZO-1 and downregulating beta-catenin and Snail. Moreover, picrasidine J reduced the expression of the serine protease KLK-10. At the signaling level, the compound reduced the phosphorylation of ERK. All these factors collectively facilitated the inhibition of HNSCC metastasis with picrasidine J. Taken together, the study identifies picrasidine J as a potential anticancer compound of plant origin that might be used clinically to prevent the distant metastasis and progression of HNSCC.

MicroRNA-375 inhibits laryngeal squamous cell carcinoma progression via targeting CST1

OBJECTIVE

This study aims to explore the effect and mechanism of miR-375 in Laryngeal Squamous Cell Carcinoma (LSCC) cell progression.

METHODS

LSCC cells (LSC-1 and TU177) were transfected with miR-375-mimic, miR-375-inhibitor or miR-375-mimic+oe-CST1. The expression of miR-375, CST1, MMP-2, and MMP-9 was measured. The effect of miR-375-mimic, miR-375-inhibitor or miR-375-mimic+oe-CST1 on cell biological functions, including cell proliferation, migration, invasion, and apoptosis, was also assessed. The potential relationship between CST1 and miR-375 was predicted by Jefferson software and validated by dual luciferase reporter gene assay.

RESULTS

Downregulated miR-375 expression was found in LSCC cells. Overexpression of miR-375 inhibited the viability and migration and promoted apoptosis of LSCC cells. Jefferson database and dual luciferase reporter gene assay confirmed that miR-375 directly targeted CST1. Overexpression of CST1 could reverse the anti-cancer effect of miR-375 overexpression in LSCC cells.

CONCLUSION

Collected evidence showed that miR-375/CST1 axis was implicated in LSCC progression.

LEVEL OF EVIDENCE

Level 3.

Serum expression of Vascular Endothelial-Cadherin, CD44, Human High mobility group B1, Kallikrein 6 proteins in different stages of laryngeal intraepithelial lesions and early glottis cancer

Background

The study was designed to evaluate the potential validity and utility of selected molecular markers in serum samples from patients with specific stages of laryngeal intraepithelial lesions that could serve as diagnostic tools in differentiation of benign and dysplastic lesions from invasive pathologies.

Methods

Prospective study included 80 consecutive patients with vocal fold lesions treated at the single otorhinolaryngology centre. All participants had surgical resection of the lesion. Blood samples were collected from each patient before the surgery. Final diagnosis was confirmed on histopathological examination and included 39 (48.75%) non-dysplastic lesions, eight (10%) low-grade dysplasia, six (7.5%) high-grade dysplasia and 27 (33.75%) invasive cancers. The ELISA procedures were performed according to the manufacturer's instruction. Individual serum concentration of selected proteins was reported in ng/ml: Vascular Endothelial-Cadherin Complex (VE-cad), CD44, Human High mobility group protein B1(HMGB1), Kallikrein 6.

Results

The highest mean levels of HMGB1, KLK6 and VE-cad were detected in sera of patients with low-grade dysplasia (81.14, 24.33, 14.17 respectively). Soluble CD44 was the most elevated in patients with non-dysplastic lesions (2.49). The HMGB1, KLK6 and VE-cad serum levels were increasing from non-dysplastic to low-grade dysplasia and followed by the decrease for high-grade dysplasia and invasive cancer, however the differences were not significant (p-values 0.897, 0.354, 0.1 respectively). Patients' serum had the highest CD44 concentration in non-dysplastic and low-grade dysplasia with the following decrease through high-grade dysplasia and invasive cancer. GERD symptomatic patients had higher levels of KLK6 and CD44 than other patients (p-value 0.06 and 0.084 respectively). There were no significant differences of biomarkers levels related to patients' gender (p-value from 0.243 to 1) or smoking status (p-value from 0.22 to 0.706).

Conclusions

VE-cad, HMGB1, CD44 and KLK6 did not prove to be reliable biomarkers implicating malignant potential within vocal fold hypertrophic intraepithelial lesions.

Diagnostic and Prognostic Value of MicroRNAs in Metastasis and Recurrence of Head and Neck Squamous Cell Carcinoma: A Systematic Review and Meta-Analysis

MicroRNAs have been proven to make remarkable differences in the clinical behaviors of head and neck squamous cell carcinoma (HNSCC). This study aims to systematically analyze whether differential expression levels of microRNAs are related to recurrence or metastasis in patients with HNSCC. A comprehensive search of the PubMed, EMBASE, and CENTRAL was conducted up to July 24^th, 2021. Data were collected and combined from studies reporting recurrence-free survival (RFS) of HNSCC patients with high microRNA expression compared to those with low expression. Besides, studies providing necessary data for evaluating the diagnostic value of microRNAs for detecting recurrence and metastasis based on their expression levels were also included and combined. The pooled hazard ratio (HR) value for the outcomes of RFS in 1,093 HNSCC samples from 10 studies was 2.51 (95%CI: 2.13–2.96). A sensitivity of 0.79 (95% CI: 0.72–0.85) and specificity of 0.77 (95%CI: 0.68–0.83) were observed in three studies, of which 93 patients with recurrence and 82 nonrecurrence controls were included, and the area under the curve (AUC) was 0.85 (95% CI: 0.81–0.88). Additionally, high diagnostic accuracy of microRNAs in detecting lymph node metastasis (LNM) was also reported. In conclusion, two panels of microRNAs showed the potential to predict recurrence or diagnose recurrence in HNSCC patients, respectively, which could facilitate prognosis prediction and diagnosis of clinical behaviors in HNSCC patients.

Direct measurement of vertical forces shows correlation between mechanical activity and proteolytic ability of invadopodia

Mechanobiology plays a prominent role in cancer invasion and metastasis. The ability of a cancer to degrade extracellular matrix (ECM) is likely connected to its invasiveness. Many cancer cells form invadopodia-micrometer-sized cellular protrusions that promote invasion through matrix degradation (proteolysis). Although it has been hypothesized that invadopodia exert mechanical force that is implicated in cancer invasion, direct measurements remain elusive. Here, we use a recently developed interferometric force imaging technique that provides piconewton resolution to quantify invadopodial forces in cells of head and neck squamous carcinoma and to monitor their temporal dynamics. We compare the force exerted by individual protrusions to their ability to degrade ECM and investigate the mechanical effects of inhibiting invadopodia through overexpression of microRNA-375. By connecting the biophysical and biochemical characteristics of invadopodia, our study provides a new perspective on cancer invasion that, in the future, may help to identify biomechanical targets for cancer therapy.

Reactivation of super-enhancers by KLF4 in human Head and Neck Squamous Cell Carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a disease of significant morbidity and mortality and rarely diagnosed in early stages. Despite extensive genetic and genomic characterization, targeted therapeutics and diagnostic markers of HNSCC are lacking due to the inherent heterogeneity and complexity of the disease. Herein, we have generated the global histone mark based epigenomic and transcriptomic cartogram of SCC25, a representative cell type of mesenchymal HNSCC and its normal oral keratinocyte counterpart. Examination of genomic regions marked by differential chromatin states and associated with misregulated gene expression led us to identify SCC25 enriched regulatory sequences and transcription factors (TF) motifs. These findings were further strengthened by ATAC-seq based open chromatin and TF footprint analysis which unearthed Krüppel-like Factor 4 (KLF4) as a potential key regulator of the SCC25 cistrome. We reaffirm the results obtained from in silico and chromatin studies in SCC25 by ChIP-seq of KLF4 and identify ΔNp63 as a co-oncogenic driver of the cancer-specific gene expression milieu. Taken together, our results lead us to propose a model where elevated KLF4 levels sustains the oncogenic state of HNSCC by reactivating repressed chromatin domains at key downstream genes, often by targeting super-enhancers.

The miRNA-kallikrein interaction: a mosaic of epigenetic regulation in cancer

The kallikrein-related peptidases (KLKs) constitute a family of 15 highly conserved serine proteases with trypsin- and chymotrypsin-like activities. Dysregulated expression and/or aberrant activation of KLKs has been linked to various pathophysiological processes, including cancer. Many KLKs have been identified as potential cancer biomarkers. microRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression by pairing to the 3' untranslated region (UTR) of complimentary mRNA targets. miRNAs are dysregulated in many cancers, including prostate, kidney and ovarian cancers. Several studies have shown that miRNAs are involved in the post-transcriptional regulation of KLKs. However, recent evidence suggests that miRNAs can also act as downstream effectors of KLKs. In this review, we provide an update on the epigenetic regulation of KLKs by miRNAs. We also present recent experimental evidence that supports the regulatory role of KLKs on miRNA networks. The potential diagnostic and therapeutic applications of miRNA-kallikrein interactions are also discussed.

Expression of human papillomavirus oncoproteins E6 and E7 inhibits invadopodia activity but promotes cell migration in HPV-positive head and neck squamous cell carcinoma cells

Background

The rapid increase in the incidence of head and neck squamous cell carcinoma (HNSCC) is caused by high‐risk human papillomavirus (HPV) infections. The HPV oncogenes E6 and E7 promote carcinogenesis by disrupting signaling pathways that control survival and proliferation. Although these cancers are often diagnosed with metastases, the mechanisms that regulate their dissemination are unknown.

Aims

The aim of this study was to determine whether the HPV‐16 E6 and E7 oncogenes affected the invasive and migratory properties of HNSCC cells which promote their spread and metastasis.

Methods and results

Invasiveness was determined using invadopodia assays which allow for quantitation of extracellular matrix (ECM) degradation by invadopodia which are proteolytic membrane protrusions that facilitate invasion. Using cell lines and genetic manipulations, we found that HPV inhibited invadopodia activity in aggressive cell lines which was mediated by the E6 and E7 oncogenes. Given these findings, we also tested whether HPV caused differences in the migratory ability of HNSCC cells using Transwell assays. In contrast to our invadopodia results, we found no correlation between HPV status and cell migration; however, blocking the expression of the E6 and E7 oncoproteins in a HPV‐positive (HPV⁺) HNSCC cell line resulted in decreased migration.

Conclusions

Our data suggest that the E6 and E7 oncoproteins are negative regulators of invadopodia activity but may promote migration in HPV⁺ HNSCC cells. Despite the need for ECM proteolysis to penetrate most tissues, the unique structure of the head and neck tissues in which these cancers arise may facilitate the spread of migratory cancer cells without significant proteolytic ability.

Targeting invadopodia-mediated breast cancer metastasis by using ABL kinase inhibitors

Metastatic dissemination of cancer cells from the primary tumor and their spread to distant sites in the body is the leading cause of mortality in breast cancer patients. While researchers have identified treatments that shrink or slow metastatic tumors, no treatment that permanently eradicates metastasis exists at present. Here, we show that the ABL kinase inhibitors imatinib, nilotinib, and GNF-5 impede invadopodium precursor formation and cortactin-phosphorylation dependent invadopodium maturation, leading to decreased actin polymerization in invadopodia, reduced extracellular matrix degradation, and impaired matrix proteolysis-dependent invasion. Using a mouse xenograft model we demonstrate that, while primary tumor size is not affected by ABL kinase inhibitors, the in vivo matrix metalloproteinase (MMP) activity, tumor cell invasion, and consequent spontaneous metastasis to lungs are significantly impaired in inhibitor-treated mice. Further proteogenomic analysis of breast cancer patient databases revealed co-expression of the Abl-related gene (Arg) and cortactin across all hormone- and human epidermal growth factor receptor 2 (HER2)-receptor status tumors, which correlates synergistically with distant metastasis and poor patient prognosis. Our findings establish a prognostic value for Arg and cortactin as predictors of metastatic dissemination and suggest that therapeutic inhibition of ABL kinases may be used for blocking breast cancer metastasis.

miR-375 Affects the Proliferation, Invasion, and Apoptosis of HPV16-Positive Human Cervical Cancer Cells by Targeting IGF-1R

OBJECTIVE

The aim of this study was to examine the relationship between miR-375 expression and the proliferation, apoptosis, and migration of cervical cancer cells. To further explore the potential target gene of miR-375, insulin-like growth factor 1 receptor (IGF-1R) was detected in miR-375 overexpressed and inhibited cervical cancer cells, which clarified the potential mechanism of miR-375 in the growth and development of cervical cancer.

METHODS

In a cervical cancer cell line (Caski), miR-375 overexpression and knockdown were achieved by transfection with a synthetic miR-375 mimic or miR-375-targeting inhibitor oligonucleotides, respectively, using siRNA-Mate transfection reagents. Real-time Polymerase Chain Reaction was performed to detect the expression level of miR-375. The functional effects of miR-375 on cell proliferation, migration, and apoptosis were evaluated using a Cell Counting Kit (CCK-8) and through scratch wound tests and apoptosis assays, respectively. Western blotting was performed to detect the expression level of the IGF-1R protein.

RESULT

Transfection with the miR-375 mimic significantly upregulated the expression of miR-375 by approximately 7.76-fold (P < 0.05), reduced cell proliferation and migration (P < 0.05), increased apoptosis (P < 0.05), and decreased the expression of the IGF-1R protein by 24.73% (P < 0.05) compared with the negative control. In contrast, transfection of the miR-375 inhibitor decreased the expression of miR-375 by 14.39% (P < 0.05), significantly increased cell proliferation and migration (P < 0.05), significantly reduced the cell apoptosis (P < 0.05), and upregulated the expression of the IGF-1R protein by 2.29-fold (P < 0.05). The cells transfected with the negative control showed no significant changes compared with the blank control for each parameter (P > 0.05).

CONCLUSIONS

miR-375 plays an important role in the tumorigenesis and development of cervical cancer. IGF-1R might represent a target gene of miR-375 in cervical cancer.

Rac3 regulates breast cancer invasion and metastasis by controlling adhesion and matrix degradation

The initial step of metastasis is the local invasion of tumor cells into the surrounding tissue. Invadopodia are actin-based protrusions that mediate the matrix degradation necessary for invasion and metastasis of tumor cells. We demonstrate that Rac3 GTPase is critical for integrating the adhesion of invadopodia to the extracellular matrix (ECM) with their ability to degrade the ECM in breast tumor cells. We identify two pathways at invadopodia important for integrin activation and delivery of matrix metalloproteinases: through the upstream recruiter CIB1 as well as the downstream effector GIT1. Rac3 activity, at and surrounding invadopodia, is controlled by Vav2 and βPIX. These guanine nucleotide exchange factors regulate the spatiotemporal dynamics of Rac3 activity, impacting GIT1 localization. Moreover, the GTPase-activating function of GIT1 toward the vesicular trafficking regulator Arf6 GTPase is required for matrix degradation. Importantly, Rac3 regulates the ability of tumor cells to metastasize in vivo. The Rac3-dependent mechanisms we show in this study are critical for balancing proteolytic activity and adhesive activity to achieve a maximally invasive phenotype.

Apolipoprotein E Promotes Invasion in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) patients generally have a poor prognosis, because of the invasive nature of these tumors. In comparing transcription profiles between OSCC tumors with a more invasive (worst pattern of tumor invasion 5) versus a less invasive (worst pattern of tumor invasion 3) pattern of invasion, we identified a total of 97 genes that were overexpressed at least 1.5-fold in the more invasive tumor subtype. The most functionally relevant genes were assessed using in vitro invasion assays with an OSCC cell line (UM-SCC-1). Individual siRNA knockdown of 15 of these 45 genes resulted in significant reductions in tumor cell invasion compared to a nontargeting siRNA control. One gene whose knockdown had a strong effect on invasion corresponded to apolipoprotein E (APOE). Both matrix degradation and the number of mature invadopodia were significantly decreased with APOE knockdown. APOE knockdown also resulted in increased cellular cholesterol, consistent with APOE's role in regulating cholesterol efflux. APOE knockdown resulted in decreased levels of phospho-extracellular signal-regulated kinase 1/2, phospho-c-Jun N-terminal kinase, and phospho-cJun, as well as decreased activator protein 1 (AP-1) activity. Expression of matrix metalloproteinase 7 (MMP7), an AP-1 target, was also significantly decreased. Our findings suggest that APOE protein plays a significant role in OSCC tumor invasion because of its effects on cellular cholesterol and subsequent effects on cell signaling and AP-1 activity, leading to changes in the expression of invasion-related proteins, including MMP7.

miR-375 Regulates Invasion-Related Proteins Vimentin and L-Plastin

Invasion is a hallmark of advanced head and neck squamous cell carcinoma (HNSCC). We previously determined that low relative miR-375 expression was associated with poor patient prognosis. HNSCC cells with increased miR-375 expression have lower invasive properties and impaired invadopodium activity. Using stable isotope labeling with amino acids in cell culture and reverse-phase liquid chromatography mass spectrometry, we assessed the impact of miR-375 expression on protein levels in UM-SCC-1 cells. Increased miR-375 expression was associated with down-regulation of proteins involved in cellular assembly and organization, death and survival, and movement. Two invasion-associated proteins, vimentin and L-plastin, were strongly down-regulated by miR-375. Luciferase reporter assays demonstrated that high miR-375 expression reduced vimentin promoter activity, suggesting that vimentin is an indirect target of miR-375. Runt-related transcription factor 1 (RUNX1) is a potential miR-375 direct target, and its knockdown reduced vimentin and L-plastin expression. Data in The Cancer Genome Atlas HNSCC database showed a significant inverse correlation between miR-375 expression and RUNX1, vimentin, and L-plastin RNA expression. These clinical correlations validate our in vitro model findings and support a mechanism in which miR-375 suppresses RUNX1 levels, resulting in reduced vimentin and L-plastin expression. Furthermore, knockdown of RUNX1, L-plastin, and vimentin resulted in significant reductions in cell invasion in vitro, indicating the functional significance of miR-375 regulation of specific proteins involved in HNSCC invasion.

MicroRNA-375 targets PAX6 and inhibits the viability, migration and invasion of human breast cancer MCF-7 cells

MicroRNAs (miRs) are a type of small non-coding RNA that serve crucial roles in the development and progression of breast cancer. However, the exact role and underlying molecular mechanism of miR-375 in mediating the growth and metastasis of breast cancer remains unknown. In the present study, reverse transcription-quantitative polymerase chain reaction and western blot analysis were conducted to examine RNA and protein expression. A luciferase reporter assay was performed to determine the association between miR-375 and paired box 6 (PAX6). The results of the current study indicate that the expression of miR-375 was reduced in breast cancer tissues compared with matched adjacent normal tissues. Transfection with miR-375 mimics led to a significant increase in levels of miR-375 in human breast cancer Michigan Cancer Foundation (MCF)-7 cells (P<0.05). The increase in miR-375 expression caused a significant decrease in the viability, migration and invasion of MCF-7 cells (P<0.05), accompanied by a reduced expression of matrix metalloproteinase (MMP) 2 and MMP9 proteins. Luciferase reporter assay identified PAX6 as a novel target of miR-375 and miR-375 in turn, negatively regulated the protein expression of PAX6 in MCF-7 cells. By contrast, overexpression of PAX6 led to a significant increase in MCF-7 cell viability (P<0.01) but did not affect the migration and invasion of MCF-7 cells, suggesting that the inhibitory effect of miR-375 on MCF-7 cell viability may be occurring, in part, via the direct targeting of PAX6.

Effect of selective small molecule inhibitors on MMP-9 and VEGFR-1 expression in p16-positive and -negative squamous cell carcinoma

The identification of molecular targets in the therapy of human papilloma virus (HPV)-associated head and neck squamous cell carcinoma (HNSCC) is a primary aim of cancer research. Matrix metalloproteinase 9 (MMP-9) and vascular endothelial growth factor receptor (VEGFR) have important roles in the development of HNSCC. The tyrosine kinase inhibitors, nilotinib, dasatinib, erlotinib and gefitinib are well established in the targeted therapy of tumors other than HNSCC. The present study aimed to investigate the alteration of MMP-9 and VEGFR-1 expression patterns following treatment with these tyrosine kinase inhibitors in p16-positive and -negative squamous carcinoma cells. MMP-9 and VEGFR-1 expression was evaluated using an ELISA in HNSCC 11A, HNSCC 14C and p16-positive CERV196 tumor cell lines, following treatment with nilotinib, dasatinib, erlotinib and gefitinib. A statistically significant reduction in MMP-9 and VEGFR-1 expression was observed in the p16-negative HNSCC 11A cells following treatment with all inhibitors (P<0.05). VEGFR-1 expression was significantly increased in p16-positive SCC cells following treatment with nilotinib, dasatinib, erlotinib and gefitinib (P<0.05). The expression of MMP-9 and VEGFR-1 was significantly altered by treatment with nilotinib, dasatinib, erlotinib and gefitinib in vitro. The results of the present study are attributed to the efficacy of the tested drugs and present potential compensatory strategies of cancer cells to avoid the antiangiogenic properties of the tested tyrosine kinase inhibitors in vitro.

Epigenetic Mechanisms of Human Papillomavirus-Associated Head and Neck Cancer

CONTEXT

Growing evidence suggests that as many as half of all oropharyngeal squamous cell carcinomas (OPSCCs) harbor human papillomavirus (HPV) infections. Despite being more advanced at diagnosis, HPV-positive OPSCCs are associated with a better response to therapy and longer patient survival than HPV-negative OPSCCs. Human papillomavirus-positive OPSCC has also been shown to have distinct host gene expression profiles compared with HPV-negative OPSCC. Recently, this distinction has been shown to include the epigenome. It is well supported that cancers are epigenetically deregulated. This review highlights epigenetic differences between HPV-positive and HPV-negative OPSCCs. The epigenetic mechanisms highlighted include methylation changes to host and viral DNA, and host chromatin modification. We also review the current evidence regarding host DNA methylation changes associated with smoking, and deregulation of microRNA expression in HPV-positive OPSCC.

OBJECTIVE

To provide an overview of epigenetic mechanisms reported in HPV-positive OPSCC, with analogies to cervical cancer, and discussion of the challenges involved in studying epigenetic changes in HPV-associated OPSCC in combination with changes associated with smoking.

DATA SOURCES

Sources were a literature review of peer-reviewed articles in PubMed on HPV and either OPSCC or head and neck squamous cell carcinoma, and related epigenetic mechanisms.

CONCLUSIONS

Epigenetic changes are reported to be a contributing factor to maintaining a malignant phenotype in HPV-positive OPSCC. The epigenetic mechanisms highlighted in this review can be studied for potential as biomarkers or as drug targets. Furthermore, continued research on the deregulation of epigenetic mechanisms in HPV-positive OPSCC (compared with HPV-negative OPSCC) may contribute to our understanding of the clinical and biologic differences between HPV-positive and HPV-negative OPSCC.