The HNC diagnosis usually includes laryngoscopy, imaging [Positron emission tomography/X-ray computed tomography (PET/CT) and magnetic resonance imaging (MRI)], and biopsy of the primary lesion ^{[31][32][33][34][35]}[31,32,33,34,35]. As technology progresses, the development of non-invasive diagnostic tools in the field of head and neck oncology has been examined; the molecular analysis of tumor’s genetic features based on circulating malignance derivatives, such as circulating tumor DNA, intact circulating tumor cells (CTCs), and exosomes in patients’ blood, namely liquid biopsy, has become a concrete possible approach to improve diagnostics, treatment planning, and post-treatment surveillance in patients with the potentially curable disease ^{[36][37][38][39]}[36,37,38,39].

Treatment possibilities include tumor resection (primary and/or secondary tumor), radical neck dissection, immunotherapy, radiotherapy, checkpoint inhibitors (mainly targeting the cytotoxic T-lymphocyte-associated protein 4 (CTLA-4)), programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), and chemotherapy ^{[40][41][42][43][44][45]}[40,41,42,43,44,45]. Recently, it has been showing how, in locally advanced HNSCC, the CTCs and the circulating tumor microemboli (CTM) have a significant prognostic impact on the potential role as predictors of induction chemotherapy benefit [46].

It is believed that the majority of oral cancers develop from oral potentially malignant lesions (OPMLs) [47]. Though they can be easily detected during screening, risk stratification is difficult. During screening, clinicians often find it difficult to distinguish OPMLs from benign lesions, and predicting OPMLs at risk of malignant transformation could be particularly challenging [47]. DNA aneuploidy has been known to be a marker of malignancy in a number of sites, including the oral cavity [47]. Indeed, DNA ploidy and chromatin organization of cells collected from OPMLs can identify lesions at high risk of progression several years prior [48]. This non-invasive test would enable clinicians to triage high-risk OPMLs for closer follow-up, while low-risk lesions can undergo less frequent biopsies, reducing the burden on healthcare resources [48]. Quite interestingly, in a study on individuals with Fanconi anemia (people with a 500-fold to 700-fold elevated risk, much earlier onset, and limited therapeutic options for oral SCC compared with the general population), a careful inspection of the oral cavity associated with brush biopsy-based cytology could identify visible oral lesions, either malignant or potentially malignant, that warrant treatment [49].

Because of the mentioned key role of genetic and epigenetic alterations in HNC, treatment protocols still include the use of alkylating agents (AAs). AAs are a heterogeneous class of drugs that interfere with the cell’s DNA and inhibit cancer cells’ growth, playing a major role in HNC [50]. These genotoxic agents modify the DNA by adding binding an alkyl group to the guanine base of DNA at the number 7 nitrogen atom of the purine ring, either directly or after metabolic conversion to reactive intermediates ^[51][52][51,52]. These drugs produce numerous side effects targeting many organs and apparats, such as the gastrointestinal tract, bone marrow, testicles, and ovaries; furthermore, most of the alkylating agents are also carcinogenic ^[53][54][53,54]. AAs still play a major role in the chemotherapeutic treatment of HNC, especially cisplatin and methotrexate, in recurrent metastatic cancer, but the focus is gradually shifting to non-conventional systemic chemotherapy, especially targeted therapy and immunotherapy, which affect the tumor microenvironment and have a potentially favorable impact on HNC management ^[55][56][57][55,56,57].

Despite the numerous proposed biomarkers in many studies, no laboratory test is sufficiently reliable alone to support a diagnosis of alcohol use disorder (AUD) ^[58][59][58,59]. Sensitivity and specificity should be high for alcohol abuse biomarkers, but in reality, they mostly fluctuate considerably and depend on the involved population. Furthermore, the ideal markers should reflect an individual’s consumption of alcohol, both chronically (screening markers) and acutely (relapse markers), and, from this, the given title of “state” markers (in contrast to the “trait” markers that predict the predisposition to develop alcoholism) ^[60][61][60,61]. The use of long-term diagnostic tools gives crucial information on the real alcohol consumption of HNC patients so that a series of recently found useful biomarkers, which can be detected in the hair, is now in the spotlight: ethyl glucuronide (EtG), fatty acid ethyl esters (products of non-oxidative ethanol metabolism), phosphatidyl ethanol, acetaldehyde adducts to protein, and 5-hydroxytryptophol ^{[18][62][63][64]}[18,62,63,64]. The main advantages of this sample material are that compounds with a relatively short lifetime in blood, but with a strong correlation to alcohol consumption, can be entrapped in the hair and are detectable for a longer time (also for years depending on the length of the hair) and at a relatively high concentration ^[64][65][64,65]. In particular, EtG and ethyl sulfate (EtS) are two non-oxidative ethanol metabolites (Figure 1) secreted by the liver which are mainly used as markers of alcohol intake related to incidents ^{[66][67][68][69][70][71]}[66,67,68,69,70,71]. These two markers for recent alcohol intake can be detected in the blood for approximately 10 h after a small to moderate alcohol intake and up to 5 days after large and repeated alcohol intakes ^[67][68][69][67,68,69]. As the efficacy of these two tests has been demonstrated in multiple settings, it has been also suggested that EtG and EtS should be included in screening tests for injured or at-risk for alcohol abuse people (including pregnant women) to investigate the possible association between residual alcohol effects and injuries, and to verify alcohol abstinence in cases of substance-related disorders ^[72][73][72,73].