In the present study, we focused on the influence of HNC treatment on oral function and QoL in HNC survivors. To the best of our knowledge, this is the first study to investigate the comprehensive relationship among HNC treatment, actual oral function, and QoL in HNC survivors by using SEM analysis.
In the SEM analysis, reconstruction surgery and neck dissection for advanced cancer were significantly related to poor oral function. This result is similar to that reported in previous studies [5, 7, 27]. Treatment for advanced cancer related to the mastication muscles can cause trismus after HNC treatment [28]. In previous studies, oral function has often been evaluated using self-report questionnaires. By contrast, the present study reports a relationship between HNC treatment and oral function evaluated objectively by a dentist.
In the SEM analysis, trismus and poor ODK were associated with poor QoL. Trismus is associated with compromised speech and poor QoL [5, 28, 33]. ODK was measured as tongue motor function related to dysarthria [18, 34]. Therefore, trismus and poor ODK appear to lead to speaking difficulties. HNC survivors reported speaking as one of the issues with the most impairment [35]. Trismus and poor ODK might affect QoL via difficulty in speaking.
In the SEM analysis, poor oral function was related to a poor QoL as evaluated by the EORTC QLQ-C30 summary score. One study showed that in HNC survivors, jaw exercise therapy increased the maximal interincisal opening and improved QoL [36]. However, no evidence was seen of effective training for improving ODK and QoL. Further studies about training for ODK are therefore needed to improve QoL in HNC survivors.
A review by von Nieuwenhuizen et al. showed strong evidence for the association between the change in global QoL from pre-treatment to 6 months posttreatment and the survival rate in HNC patients. They suggested that improving QoL may be an interesting intervention to improve survival rates [37]. Rehabilitation for oral function improved QoL [36]. Rehabilitation for oral function by dental staff might be necessary in posttreatment for improving QoL and survival rates, in addition to perioperative oral management. Our findings suggest the need to provide dental interventions for long time in HNC survivors after cancer treatment.
Advanced age was significantly associated with poor QoL in the SEM analysis. This result is opposite to those reported in previous studies [7, 38]. Laraway suggested that older individuals may be better adapted to a poor body image after treatment and are generally likely to be less conscious of body image [39]. In these studies, QoL was evaluated based on mean University of Washington Quality of Life (UW-QoL) instrument subscale scores (functioning, economic status, and symptoms) or the mean cancer-specific QoL score (appearance, economic status, and distress) of Quality of Life in Adult Cancer Survivors (QLAS) [7, 38]. In the present study, QoL was evaluated based on the EORTC QLQ-C30 summary score, which was calculated from the mean subscale scores (health status, functioning, and symptoms). Older people generally have worse oral function. Compared with UW-QoL and QLAS, the EORTC QLQ-C30 summary score may be easily influenced by actual oral function.
Advanced age was significantly associated with a lower QoL score and poor oral function in the SEM analysis. Japan is a super-aging society, with about 30% of its citizens already aged > 65 years [40]. As a result, an increase in older HNC patients and survivors is expected in Japan. Older people were significantly more likely to have poor oral function [41]. Older HNC patients and survivors might have lower oral function and poorer QoL. Therefore, the need for rehabilitation to improve oral function is increasing after HNC treatment to improve QoL.
However, the patients in the present study may not represent a specific population. First, the mean tongue pressure (24.7 kPa) was similar to that reported in previous studies (25.5 kPa) of Japanese HNC survivors using the same device [Tashimo Y, 2019]. Second, the mean global health status (69.3) (data not shown) was within the range of previous studies (61.6–73.6) using the same questioner [9, 42]. Therefore, a multi-center study is needed to extrapolate these findings to general HNC survivors.
This study has some limitations. First, this was a cross-sectional study. To clarify the causal relationship, a prospective cohort study and an interventional study would be needed. Second, we did not consider other important confounding factors such as education level, marital status, and income [5, 43].