Discussion
Our study evaluated age-related trends in HNC (oral cavity, pharynx, oropharynx, hypopharynx) from 1975 to 2016. This was done in order to visualize proportional changes in young (0-39 years old), middle-aged (40-59 years old) and elderly (60+ years) patients. The results demonstrated that the mean age at diagnosis of the four HNC subsites combined has increased in the last four decades and similar trends can be seen within every subsite of HNC, with the exception of oropharyngeal cancer. The increased age at diagnosis reflects similar trends in the aging of the United States population (20,21,22). Individuals in the U.S. are living longer (21,21,22), and this is likely a contributing factor to the increasing age of cancer patients.
In the context of oral cavity cancers, there is an increase of mostly young patients and a decrease in middle-aged patients (Table 3). The oral cavity is the only HNC subsite exhibiting a true proportional increase in young patients (Table 3). Cancers of the oral cavity have encompassed a smaller proportion of HNC over time and exhibit a decreasing incidence over the last 40 years (Table 1). From the 1950s to the 1980s, the incidence of oral cavity cancer increased significantly in young white males, which was attributed to tobacco usage (23,24,25). However, when looking specifically at the female population, the incidence of oral cavity cancers has steadily increased from 2008 and onwards. These results support similar findings of increased incidence of oral cavity cancers in women in recent years (13,14) and case reports of very young patients presenting with oral cavity tumors (15,16).
In the context of oropharyngeal cancers, there is an increase in middle-aged patients and a decrease in young and elderly patients (Table 3). Additionally, we found that oropharyngeal cancer is the only subset of HNC that exhibits an increase in incidence in both males and females. These findings are echoed in many other studies (4,5,9,10). This increase in incidence has been attributed to the rising HPV epidemic and oral sex practices in the United States (4,5,8,10,11). When observing statistics from HPV-induced cervical cancers, infection is usually acquired between 20-30 years of age (26), and incidence of cervical cancer peaks around 20-30 years after beginning sexual activity (27). This places peak incidence of cancer at 40-60 years of age. Similar results are seen when evaluating for HPV-induced oropharyngeal cancer. A Canadian study by Claudie et al . (28) found that most individuals within the study began oral sex practices between the ages of 17-30, and that risk of oropharyngeal cancers increased significantly 30 years after this time. This places the highest risk of HPV-induced oropharyngeal cancer at above 47 years of age, which is confirmed by our results of higher proportions of middle-aged individuals acquiring oropharyngeal cancer (Table 3).
When assessing laryngeal cancers, there is an increase in elderly patients, and a decrease in middle-aged and young patients (Table 3). hese results are contradictory to previous case reports (17,18) and do not support the concerns that this cancer is occurring at younger ages. The proportion of young people diagnosed with laryngeal cancer has decreased in the last 40 years and laryngeal cancer patients are actually getting older at the time of diagnosis (Table 3). A Lithuanian study by Jasevicieneet al . (29) echoes these findings and quantifies the aging of the laryngeal cancer population. They report that the mean age at diagnosis of laryngeal cancer is increasing annually by 0.1566 years for men and 0.0602 years for women in Lithuania (29).
A higher proportion of elderly patients is also being diagnosed with hypopharyngeal cancer (Table 3), and hypopharyngeal cancer encompasses a smaller proportion of HNC cases now than in 1975 (Table 1). Another U.S. population study by Kuoet al . reports similar findings (30). However, hypopharyngeal cancer incidence has been noted to increase in France and some Asian countries This has been attributed to increased tobacco use (31).
Aside from age, an interesting trend observed in our gender-stratified HNC analysis was that the percentage of young (0-39 years) HNC patients is much higher in females than males (4.1% women vs. 3.0% men; Table 4). However, overall cases of HNC are approximately three times higher in men than in women. In other words, men are more likely than women to present with HNC, but the women with HNC are more likely than men to present with the cancer at a young age.
Previous studies have addressed epidemiological trends of HNC, but they did not clearly identify proportional changes amongst age cohorts over time, leaving us to wonder if HNC patients are truly becoming younger. Bean et al. utilized the SEER database to evaluate differences in survival between small cell and squamous cell HNC. Although the study does show a breakdown of HNC age and subsite separately, it does not show age cohorts within the subsites, nor does it demonstrate temporality as does ours (32). A 2015 study by Gillison et al. touched on our primary question of age and HNC, but is restricted to oropharyngeal cancer and focuses on incidence, not proportional change of age cohorts over time (33). Mourad et al. similarly touched on HNC and age, but they focused on incidence, not proportional age prevalence, within a single decade and do not show subsites (4). While these studies, and many others, highlight interesting trends of HNC epidemiology, the primary question of whether patients are becoming younger or older has not been clearly addressed. Our study directly examines the relative change of prevalence between age cohorts over several decades. Our study also has the virtue of looking at multiple HNC subsites over the entire history of the SEER registry.