In 2020, head and neck cancer (HNC) ranked as the 7^th most prevalent cancer globally, comprising 4.8% of all incident cancer cases and 4.7% of all cancer deaths (1). HNC includes cancers in the lip and oral cavity, salivary glands, nose, middle ear, pharynx, and larynx, most of which are squamous cell carcinomas (2). In addition to smoking and alcohol use, exposure to betel quid, wood dust, radiation, and genetic risk factors is also associated with the risk of HNC (2). HPV infection has also been identified as a risk factor for HNC, particularly squamous cell carcinoma (2). During the last decades, a decreasing incidence and mortality of HNC have been noted, likely because of decreasing tobacco use (3, 4).

Cancer-related inflammation is one of the seven hallmarks of cancer (5, 6). Cancer can promote the expression of inflammation-related factors such as interleukins and chemokines (7), whereas inflammation can promote cancer progression by regulating the immune microenvironment through a cascade of inflammatory factors such as cytokines and infiltrating leukocytes (8). Many studies have therefore examined the roles of different inflammatory biomarkers (e.g., haptoglobin, C-reactive protein [CRP], albumin, platelets, sedimentation rate, leukocytes, lymphocytes, monocytes, and neutrophils) in the risk of different cancers, including HNC (9–50). Different mechanisms might underlie the link between these biomarkers and cancers. For instance, metabolic dysfunction has been proposed as a potential pathway linking together altered expression of haptoglobin and different malignancies (51, 52) whereas a high level of sedimentation rate might indicate presence of inflammation and tissue damage in the body, which could subsequently influence the risk of cancers (37, 53). Similarly, the profiles of different immune cells have been studied extensively in cancer development and progression, as immune system function is critically involved in the initiation and progression of cancers (54). Although most of the studies found a difference in inflammatory biomarkers between patients with HNC and individuals free of HNC, there is a concern of potential reverse causation as most of these studies are case-control studies with biomarker measurements after a diagnosis of HNC. Large-scale prospective studies are therefore needed to confirm or refute these findings. Furthermore, few studies have examined HNC by histopathology type or cancer site or examined a comprehensive panel of inflammatory biomarkers commonly measured clinically.

To this end, we conducted several analyses using the Swedish Apolipoprotein-Related Mortality Risk (AMORIS) Cohort, including a sample size of over half a million and a follow-up of up to 35 years, with the aim of evaluating the association between the baseline level of blood inflammatory biomarkers that are commonly measured clinically (e.g., CRP, haptoglobin, albumin, platelets, sedimentation rate, and counts as well as frequencies of immune cells) and the subsequent risk of HNC, focusing on analyzing HNC by histopathology type and cancer site. We also performed a nested case-control study to examine the temporal trends of these biomarkers during the three decades prior to diagnosis of HNC.

The study cohort included 542,433 participants with a mean age of 45.03 at baseline ( Table 1 ). During a mean follow-up of 20.36 years, we identified a total of 2,510 newly diagnosed HNC cases.

Based on a cohort study of more than half a million participants with up to 35 years of follow-up, our study showed that individuals with a higher blood level of haptoglobin, leukocytes, sedimentation rate, and monocytes had an elevated risk of HNC, whereas those with a higher blood level of lymphocytes in % and LMR had a lower risk of HNC. The associations were mainly noted for squamous cell carcinoma, as well as for cancers in the lip and oral cavity, larynx, and pharynx. We also found that individuals with HNC exhibited higher-than-expected levels of haptoglobin, leukocytes, sedimentation rate, and monocytes, as well as lower-than-expected levels of lymphocytes in % and LMR, during the 30-year period prior to cancer diagnosis.

In our literature review, we identified five case-control studies (20–24) that assessed the role of haptoglobin in HNC risk. Four of these studies found a higher level of haptoglobin in patients with oral squamous cell carcinoma (OSCC) (21–23) or laryngeal cancer (24), compared to controls, in agreement with our finding. One study found, however, a lower level of haptoglobin among patients with OSCC than controls (20). The inconsistent results may be due to different reasons, including potentially different measurements of haptoglobin, as patients with HNC might have a higher level of haptoglobin α2 chain but a lower level of haptoglobin α1 chain (62). In terms of leukocytes, we identified one cohort study (12) and seven case-control studies (12, 26, 31–34, 36, 38). The cohort study reported a positive association between the level of leukocytes and the risk of cancer in the oral cavity and pharynx (12), in line with our finding. Out of the seven case-control studies, four studies found elevated levels of leukocytes in patients with nasopharyngeal carcinoma (31), laryngeal cancer (33), OSCC (26), and head and neck squamous cell carcinoma (HNSCC) (38), while the rest reported no difference between patients with HNC and controls (32, 34, 36). In terms of sedimentation rate, we identified one cohort study (37) and one case-control study (18). The cohort study reported that an elevated sedimentation rate was associated with an increased risk of cancers in the lip and oral cavity, the salivary glands, and the pharyngeal cavity and tonsils, a decreased risk of larynx cancer, and no altered risk of cancer in the tongue (37). The case-control study reported an elevated levels of sedimentation rate in patients with HNSCC compared to controls (18). Finally, we identified four case-control studies on monocytes and risk of HNC (26, 29, 31, 38). Three of the four studies reported an elevated level of monocytes in patients with nasopharyngeal cancer (31), OSCC (26), and HNSCC (38), compared to controls, in agreement with our finding. One study reported, however, no difference between patients and controls (29). Taken together, the existing studies, mostly cross sectional in nature, and the present study, using a time-to-event analysis of prospectively collected data, jointly suggest a positive association between blood levels of haptoglobin, leukocytes, sedimentation rate, and monocytes and risk of HNC, especially squamous cell carcinoma.

When it comes to lymphocytes, we identified five case-control studies (26, 29, 31–33) in our literature review. Three studies reported a lower level of lymphocytes in patients with cancer in the salivary glands (29), nasopharyngeal cancer (31), or cancer in the oral cavity (32), while two reported an elevated level of lymphocytes in patients with laryngeal cancer (33) or OSCC (26), compared to controls. Although we did not find statistically significant results for total count of lymphocytes, we found a higher level of lymphocytes in % or LMR to be associated with a lower risk of HNC. More studies are therefore needed to further understand the role of lymphocytes in the risk of NPC, both in absolute and relative quantities.

Apart from the above six biomarkers, we did not find clear results for any of the other six biomarkers studied. For instance, we identified two cohort studies (9, 12) and nine case-control studies (10, 11, 13–19) that assessed the association of CRP with the risk of HNC. The cohort studies found an increased risk of HNC in relation to a higher level of CRP (9, 12). Eight case-control studies found a higher level of CRP in patients with HNC, compared to controls, whereas one study found no difference between cases and controls (16). The null finding of CRP in the present study might be since we did not measure high sensitivity CRP as it was not available in Sweden in the recruitment period of the AMORIS Cohort. Our study did not reveal clear association between albumin level and risk of HNC. To our best knowledge, three case-control studies have examined albumin in HNC so far (25–27). Two studies reported a lower level of albumin in patients with OSCC (25, 26) whereas the other reported a lower level of albumin in patients with oral cancer (27). We found a positive association between the level of platelets and the risk of squamous cell carcinoma but not any HNC or adenocarcinoma in the present study. In the literature review, we found ten case-control studies in this regard (26, 28–36). Three reported an elevated level of platelets in patients with OSCC (26, 28) or nasopharyngeal carcinoma (31), when compared to controls, whereas the other seven did not find a difference between cases and controls (29, 30, 32–36). Finally, we did not find neutrophils to be associated with the risk of HNC in the present study. In the literature review, we identified seven case-control studies (26, 29, 31–33, 36, 38), including five studies that reported an elevated count of neutrophils in patients with cancer in the salivary glands (29), nasopharyngeal cancer (31), laryngeal cancer (33), OSCC (26), or HNSCC (38), compared to controls, as well as two studies reporting no difference between patients with cancer in the oral cavity (32) or laryngeal squamous cell carcinoma (LSCC) (36) and controls. In terms of PLR, ten case-control studies were identified in the literature review (28–30, 39–45). Eight studies reported an elevated level of PLR in patients with LSCC (39), nasopharyngeal cancer (40), cancer in the salivary glands (29, 44), larynx and hypopharynx cancer (42), parotid cancer (30), HNC (43), and laryngeal cancer (45), whereas two reported no statistically significant difference between patients with OSCC (28) or parotid cancer (41) and controls. In terms of NLR, 18 case-control studies were identified in our literature review (29, 30, 32–34, 36, 38–41, 43–50), including 17 studies reporting a higher level of NLR in patients with HNC, compared to controls, and one study reporting no difference between patients with laryngeal cancer and controls (47). Finally, like lymphocytes in % and LMR discussed above, there is currently no other study on monocytes in %, neutrophils in %, or CAR concerning the risk of HNC. Regardless, for all biomarkers discussed herein, the contrasting findings between the present study and the previous studies might have importantly been attributed to reverse causation, as the previous studies mostly measured biomarker levels following a diagnosis of HNC. For instance, one might speculate that inflammation level (e.g., CRP, neutrophils, and NLR) might increase whereas albumin level might decrease following a cancer diagnosis, because of cancer biology, cancer treatment, or both.

A link between blood inflammatory biomarkers and the risk of HNC is biologically plausible, as chronic inflammation has been hypothesized to promote HNC development and progression (6, 63). For instance, recent studies have shown that haptoglobin is a highly complex glycoprotein containing four N-glycosylation sites and is characterized by highly sialylated N-glycans (64). This complex glycosylation pattern makes haptoglobin particularly susceptible to altered glycosylation, which might influence tumor development and progression (65). Our findings suggest that blood inflammatory markers are primarily associated with HNSCC instead of adenocarcinoma. One reason might be the different molecular pathogenesis between squamous cell carcinoma and adenocarcinoma. Genetic instability is more commonly observed in patients with HNSCC, compared to adenocarcinoma. For example, TP53 mutations are present in 70.4% of squamous cell carcinoma but only in 28% of adenocarcinoma (66, 67) and inflammation has been suggested to increase DNA damage and mutations via generating reactive oxygen species (68). Another reason is the difference in risk factors between squamous cell carcinoma and adenocarcinoma. For instance, HPV infection has been suggested as a risk factor for HNSCC, especially oral and oropharyngeal squamous cell carcinoma (2), but is very rare in head and neck adenocarcinoma (69). Further, inflammation-related cytokines are known to regulate HPV proliferation and modulate its oncogenes E7 and E8 in cervical epithelial cells (70). Similarly, inflammation was shown to be associated with HPV infection status of tongue squamous cell carcinoma (71). Finally, the limited number of individuals with adenocarcinoma might also have contributed to a lack of statistical power in the analyses of adenocarcinoma.

This study has several strengths. First, the study has a large sample size, a population-based design, prospectively collected data on inflammatory biomarkers, and a long and complete follow-up, reducing the risk of selection bias due to selective study participation or loss to follow-up as well as random error. Second, we estimated the associations by histopathology type and site of HNC to investigate whether the roles of the studied biomarkers might differ by these factors. Third, to minimize the possibility of reverse causation, we excluded the initial five years of follow-up from the analysis. Additionally, we conducted a nested case-control study to estimate the temporal trends of the studied biomarkers during 30-year period prior to cancer diagnosis, which corroborated findings of the time-to-event analysis. For example, specific biomarkers, such as haptoglobin and leukocytes, which were shown to have positive associations with the risk of HNC in the time-to-event analysis, demonstrated higher-than-expected levels during the 30-year period prior to cancer diagnosis among individuals with HNC. Finally, a sensitivity analysis was performed to address potential indication bias by restricting the analysis of biomarker measurements obtained during an occupational health check-up. There are also limitations in this study. Given the register-based nature of the present study, the main limitation is the inability to study the contributors to the altered blood inflammatory biomarkers. For instance, tobacco smoking has been associated with an altered level of inflammatory biomarkers (72), including haptoglobin, CRP, and count of leukocytes (73). As a result, our findings on these biomarkers might indicate an indirect effect of tobacco smoking on the risk of HNC. Further, the nested case-control analysis was based on a well-defined cohort with complete follow-up and included cases and controls individually matched by age, sex, and calendar period of recruitment to the AMORIS Cohort, using the method of incidence sampling. However, although the cases and controls had identical time window for assessment of biomarker levels given the design, the cases and controls did not always have the same number of repeated measurements for each biomarker during the time window. It is possible that individuals with an upcoming cancer diagnosis had more measurements, compared to others. This will however most likely affect the result patten noted during the last few years, but not the entire 30 years, before cancer diagnosis.

In this large cohort study with prospectively measured blood inflammatory biomarkers, we found a positive association of haptoglobin, leukocytes, sedimentation rate, and monocytes, and an inverse association of lymphocytes in percentage and LMR, with the risk of HNC. Our findings therefore provide solid evidence supporting the presence of alterations in blood inflammatory biomarkers during the decades before the diagnosis of HNC.

The datasets presented in this article are not readily available because Data and materials used in the present study are not publicly available due to EU and Swedish regulations. Please contact the Steering Group for AMORIS Cohort for more information and potential collaborations (https://ki.se/imm/amoris). Requests to access the datasets should be directed to https://ki.se/imm/amoris.

The studies involving humans were approved by Swedish Ethical Review Authority. The studies were conducted in accordance with the local legislation and institutional requirements. Written informed consent for participation was not required from the participants or the participants’ legal guardians/next of kin in accordance with the national legislation and institutional requirements.

YY: Conceptualization, Data curation, Formal Analysis, Investigation, Writing – original draft. YL: Data curation, Investigation, Writing – original draft, Conceptualization. FS: Investigation, Methodology, Visualization, Writing – review & editing. MF: Investigation, Methodology, Resources, Writing – review & editing, Project administration. NH: Investigation, Methodology, Resources, Writing – review & editing, Project administration. FF: Funding acquisition, Writing – review & editing, Resources, Investigation, Methodology. ZZ: Investigation, Supervision, Writing – review & editing, Funding acquisition, Project administration, Conceptualization, Methodology. QL: Supervision, Writing – review & editing, Investigation, Conceptualization, Methodology, Visualization, Formal Analysis.