1. Introduction
Squamous cell carcinoma (SCC) is the second most common skin cancer, following basal cell carcinoma [
1]. It typically arises with precancerous lesions, often in sun-exposed regions, notably the head and neck. Risk factors for the development of SCC include ultraviolet (UV) radiation, chemical carcinogens, genetic predisposition, immunosuppression, drugs, and viral infection [
1]. Viral infections, particularly those caused by the human papillomavirus (HPV), are considered a potential carcinogen that indirectly impair DNA repair mechanisms or apoptotic responses to UV-induced damage [
1]. The carcinogenic potential of HPV infection in SCC is relatively well-known, particularly in cases of epidermodysplasia verruciformis (EV). EV, an autosomal recessive hereditary dermatosis, presents a heightened risk for SCC development and exhibits high susceptibility to infection with beta-genus HPV-5 and HPV-8 [
2]. In EV, SCC develops in chronically HPV-infected skin, particularly in sun-exposed areas [
2]. Numerous studies have investigated the occurrence of HPV in oropharyngeal SCC (OPSCC) [
3]. However, studies on the relationship between HPV and non-oropharyngeal cutaneous SCC (head and neck cutaneous squamous cell carcinomas [HNCSCC]) are limited. In addition, most studies have been conducted on Caucasians, and few studies have been conducted on Asians.
p53 is an important driver mutation in SCC with a tumor suppressor function against UV-induced damage [
4]. However, to the best of our knowledge, no studies have been conducted on the p53 mutation rate in HNCSCC and its association with HPV, which is known to interfere with the repair of UV-induced damage. P16 is known as a surrogate marker for HPV with a high positive predictive value (PPV) in OPSCC and is associated with a favorable prognosis [
5]. However, its association with HNCSCC has not yet been studied.
This study aimed to examine the relationship between HPV infection and HNCSCC in an Asian population. Additionally, we investigated the positivity rates of p53 and p16 in HNCSCC and their association with HPV.
4. Discussion
SCC is the second most common type of non-melanoma skin cancer, accounting for approximately 40.2% of malignancies in the head and neck region [
6]. Several risk factors for the development of HNSCC have been identified, including tobacco smoking, alcohol consumption, dietary factors, and HPV infection [
7]. The role of HPV in oral and oropharyngeal carcinogenesis was first described by Syrjanen et al. in 1983 [
8]. Since then, numerous studies have investigated the role of HPV in HNSCC, particularly in OPSCC. The HPV-positivity rate in OPSCC varies widely, typically ranging from 40% to 80%, depending on the sensitivity and specificity of the detection method used [
3].
Notably, HPV-positive OPSCC exhibits distinct clinical and demographic characteristics compared to those of HPV-negative tumors [
9]. For instance, HPV-positive OPSCC is more frequently observed in certain regions, such as the United States, than in Asia or Europe [
10]. This geographical variation in HPV prevalence may be attributed to differences in sexual behavior, cultural practices, and HPV vaccination rates. Moreover, HPV-positive OPSCC tends to occur more frequently in younger patients and individuals with a history of multiple sexual partners and higher oral sex exposure [
11]. These behavioral risk factors contribute to the transmission of HPV, particularly high-risk HPV genotypes such as HPV-16 and HPV-18, which are associated with oncogenic transformation and the development of OPSCC. Importantly, HPV-positive OPSCC is associated with a more favorable prognosis compared to that of HPV-negative tumors [
12,
13,
14]. This improved prognosis is thought to be related to the distinct molecular and biological characteristics of HPV-positive tumors, including overexpression of the p16 protein and inactivation of the p53 tumor suppressor gene. These molecular alterations contribute to enhanced sensitivity to radiotherapy and chemotherapy, resulting in better treatment responses and overall survival rates in HPV-positive OPSCC patients [
15,
16,
17].
Clinically, HPV-positive OPSCC typically presents as a single localized tumor in the oropharynx, most commonly in the tonsillar region or base of the tongue [
18]. These tumors often have a smaller primary tumor size and a lower rate of lymph node involvement than that of HPV-negative tumors [
19,
20]. Unlike HPV-negative tumors, HPV-positive OPSCC are less frequently associated with tobacco and alcohol use, and patients may present with fewer comorbidities and a better performance status at the time of diagnosis [
21].
Unlike OPSCC, HNCSCC has been relatively understudied. However, the HPV infection rate is higher in SCC, including those occurring in the head and neck regions, than in normal skin [
22]. UV exposure, a known trigger for SCC, can induce immunosuppression, potentially increasing susceptibility to HPV infection. Conversely, evidence suggests that HPV infection may exacerbate UV-induced damage, potentially contributing to the development of SCC. Nevertheless, its role in the maintenance of SCC remains uncertain [
23]. Previous studies have reported HPV positivity rates in HNCSCC ranging between 5% and 20%; however, it is unclear whether HPV is directly involved in the pathogenesis of HNCSCC [
13,
24]. Furthermore, most studies have been conducted in Caucasian populations, with few examining the role of HPV in HNCSCC among Asians [
3].
In this study, the positive detection rate of HPV through IHC for HNCSCC was 8.06% (5/62). This was lower than that reported in a previous study using the polymerase chain reaction (PCR) method for North Americans, where the HPV positivity rate was 21.8% [
25]. The difference in test methods is considered one of the reasons for this result. PCR testing is the most sensitive method for detecting HPV [
26], and it may show a higher positivity rate than the IHC method used in this study. In addition, as mentioned above, HPV-positive OPSCC occurs more frequently in the United States than in Asia [
10], and because of similar racial and cultural differences, HPV-positive HNCSCC is also thought to be lower than that reported in previous studies targeting North Americans.
p53 is the most commonly mutated gene in SCC, occurring in up to 90% of cases [
27]. When a mutation occurs, tumor cells resist apoptosis and cell cycle arrest, leading to clonal expansion. Mutations in p53 caused by UV damage are involved in the development of SCC [
4]. In the past, studies have been conducted on the effect of p53 overexpression on treatment response or prognosis in HNCSCC, but no consensus has been reached [
28]. In addition, a study was conducted on the association between the presence of HPV and p53 in SCC. HPV E6 and E7 proteins suppress p53-mediated gene transcription. This may interfere with the UV-activated cell cycle checkpoint, exacerbating UV-induced DNA damage and ultimately the oncogenic potential of HPV [
29,
30,
31].
In this study, p53 was overexpressed in 72.58% (45/62) HNCSCC patients. This is similar to the 79% reported in previous studies on SCC Korean patients [
32]. The incidence of UV-induced SCC is inversely proportional to latitude, and the closer it is to the equator, the higher the incidence [
33]. Moreover, the incidence is higher in the UV-sensitive fair skin type than in the dark skin type. This study was conducted in South Korea, and the frequency of p53 mutations caused by UV damage was anticipated to be lower than that reported in previous studies on Caucasians [
32], but there was no significant difference. In addition, no significant association was observed between HPV and p53 expression in HNCSCC (p>0.99).
P16 has emerged as a cost-effective surrogate marker for HPV in OPSCC owing to its high sensitivity and specificity in detecting HPV-related tumors. IHC staining for p16 can reliably identify tumors with transcriptionally active HPV, making it a valuable tool for diagnostic and prognostic purposes. Additionally, p16 expression in OPSCC has been associated with a favorable prognosis, as HPV-positive tumors generally exhibit a better response to treatment and improved survival outcomes than that of HPV-negative tumors. However, the role of p16 in HNCSCC remains unclear. A study including HNCSCC patients reported that p16 expression was not related to high-risk HPV or prognosis [
34]. The positivity rate of p16 in this study was 38.71% (24/62), which is similar to 31.9% in a previous study on HNCSCC. The PPV of p16 for HPV was 8.33%, which was very low compared with 92.9% for OPSCC in a previous study [
34], and there was no significant relationship between HPV and p16. (p>0.99) This suggests that the relationship between p16 expression and HPV status may differ between OPSCC and HNCSCC, highlighting the need for further research to elucidate the role of p16 in HNCSCC pathogenesis and its potential utility as a prognostic biomarker.
One possible explanation for the low positivity rate of p16 in HNCSCC is the influence of UV radiation exposure, a known risk factor for cutaneous SCC. UV exposure induces DNA damage and promotes genomic instability, leading to the accumulation of mutations in key regulatory genes such as p53, which may disrupt normal cell cycle regulation and override the compensatory mechanism of p16 overexpression in HPV-related OPSCC [
23]. Furthermore, other environmental and genetic factors specific to cutaneous SCC may modulate p16 expression independently of HPV status, further complicating its utility as a prognostic biomarker for HNCSCC. Overall, the contrasting positivity rates of p16 in OPSCC and HNCSCC highlight the complex interplay among HPV infection, UV radiation exposure, and other etiological factors in the pathogenesis of head and neck cancer. Further research is required to elucidate the mechanisms underlying p16 expression in HNCSCC and its potential prognostic significance in these tumors.
The location of HNCSCC was classified as Area H and the Area M to indirectly confirm the relationship between p16 expression and HNCSCC prognosis. According to the National Comprehensive Cancer Network guidelines, SCC located in Area H has a high probability of recurrence and metastasis and requires Mohs microsurgery [
35]. In this study, the relationship between p16 and tumor location was not statistically significant (p=0.444), indication no correlation between p16 and a favorable prognosis in HNCSCC.
This study has several limitations that should be acknowledged. First, it was conducted at a single institution and focused on a specific racial demographic, which may limit the generalizability of the findings to other populations. Additionally, the sample size was relatively small, comprising only 62 cases with a limited number of HPV-positive samples. Furthermore, HPV, p16, and p53 statuses were determined using IHC staining methods rather than more sensitive techniques such as PCR. While IHC staining is commonly used for clinical diagnosis, its sensitivity and specificity for detecting HPV and other molecular markers may vary, potentially leading to the misclassification of cases [
36]. Moreover, the lack of direct information on survival outcomes and prognosis limits the assessment of the long-term implications of HPV, p16, and p53 expression patterns on patient outcomes.