This study assessed the epidemiological demographic, clinical, epidemiological, histopathological and surgical characteristics of OSCC in Qatar. In terms of gender, the majority of our patients were males, with a M:F ratio of ≈ 10.9:1. Hence our findings support that OSCC has a male predominance globally [13]. The global OSCC M:F ratio is about 5.5:2.5 [33], ranging from 1.2:1 [5] to 3.02:1 [16]. Such range is similar to most Arab nations [7]. Our OSCC M:F ratio was the highest worldwide, probably due to the unique demographics in Qatar. The large numbers of single young male workers and expats working in Qatar have resulted in a country having has the highest M:F ratio worldwide (3.15:1) [32].
As for age, globally, most OSCC patients are > 45 years of age at first diagnosis, [median 62 years], with only 6% of patients < 45 years [12]. In contrast, about one third of our patients were < 41 years, a proportion that is significantly higher than other studies globally [13, 6, 9] and regionally [20]. Our sample’s mean age was 46.9 years (range 18–78), suggesting that OSCC patients in Qatar are slightly younger than their counterparts in the region [7]. Again, this is probably because the majority of the population in Qatar are young and middle-aged individuals [32]. Age groups correlation was studied against multiple parameters [T-stage, N-stage, grade, lymphovascular and perineural invasion] and no statistically significant correlation was identified.
In terms of nationality, most patients were not Qatari nationals. Indians comprised largest proportion of OSCC our patients (39.6%), reflecting the country’s demographics, as Indians are the largest ethnic group of the expat population living in Qatar [34]. Individuals from South Asian countries were also well represented, in agreement with the higher OSCC incidence in South Asia [5].
The most common site of primary tumor in the current study was the tongue (53.2%), in contrast with other studies where buccal mucosa was the most common location, especially in South Asians [e.g., 16]. Nevertheless, our finding is in concordance with most of published literature, where the tongue was the most common [15, 7, 35, 13, 12].
The current study observed a mean DOI of 8.8 mm (median 7 mm, range 1.5–25 mm), slightly deeper than the 5.7 mm mean DOI reported in United Kingdom [12] and 6.3 mm in Finland [36], although it was less than the 12.9 mm reported in one international multicenter study [37]. DOI in OSCC is an important variable in predicting nodal metastasis and hence it impacts on the management and prognosis [38].
Pathological staging is a prognostic factor, where the T-stage (primary tumor) is an important factor in selecting the management option and predicting nodal metastasis, recurrence and survival [12]. A majority of our sample (66%) was early stage (T1 and T2), probably attributed to an efficient cancer referral system in Qatar that is vigilant for suspected cancer patients, and hence the early referral and detection. However, the N-stage is also another key prognostic factor, where generally, about half the OSCC patients have nodal metastasis at diagnosis [39]. Across our sample, 50.5% of patients who underwent resection had no nodal metastasis, while 17.5% were N1 stage. A proportion of patients who underwent resection [14.6%] did not undergo neck dissection at surgery, and subsequently were classified as NX. Our practice is in line with others, where the decision to sample cervical lymph nodes is usually based upon the primary tumor [T-stage], with the T1 patients spared from neck dissection if radiologically not suspicious [3]. Therefore, our finding of NX patients is probably due to the early stage nature of the disease among the majority of our sample.
The World Health Organization’s classification grades OSCC as well differentiated (Grade 1), moderately differentiated (Grade 2) and poorly differentiated (Grade 3), based upon the pathologist’s evaluation of keratinization, pleomorphism, and mitosis [12]. Globally, whilst many OSCC are low histological grade, grade 2 moderately differentiated tumors form the majority of cases [13, 15]. The current study is in agreement, since the majority of patients (50%) were grade 2 followed by grade 1 (29.2%) [Figure 1].Some researchers employ grade as a part of the risk-assessment to predict prognosis and survival [17].
In terms of the histological variants of OSCC, some authors have linked particular variants with better prognosis and other variants with less favorable outcomes [40]. Generally, the conventional variant comprises a majority of the cases, with other variants involving up to 15% of cases [41]. We are in support, the conventional variant in the present study comprised a majority (97.4%), with each of the other six variants each having a single case (0.6% each) (Fig. 2).
The margin status in the main resection specimen has special significance since its involvement is a negative prognostic factor, implying increased recurrence and poorer survival [18]. Of the resection cases in the current study, 10.6% had positive margin in the main resection specimen, 37.5% had negative margin (> 5 mm clearance), and more than half had close margin [negative but < 5 mm clearance]. Our proportion of cases with close margins was higher than other studies [e.g., 12, 5], probably due to the high dependence of surgeons at our institution on the tumor bed margin frozen section [performed in 84.5% of eligible cases] that provides surgeons with high certainty of the completeness of the excision. Such certainty is evidenced by that across our sample, tumor bed was submitted for frozen section in 84.5% of eligible cases, and of those which were submitted, only one case was positive while all remaining cases were negative. Notwithstanding, the importance of intraoperative margin sampling and examination by frozen section [tumor bed margin sampling] to outcomes remains controversial, with some authors suggesting that this practice has no effect on survival and outcome [15].
A body of research defines follow-up for recurrence and survival at 3 and 5 year milestones [e.g., 12] with a minority implementing a 2 and 5 year time points [9]. In our 100 resection cases where follow-up data was available, mean follow-up period was 2.38 years, slightly less than the 3 years criteria, probably attributed to the fact that most of our OSCC patients were not Qataris, with many returning to their home countries after initial treatment in Qatar
Local recurrence is a key prognostic factor in OSCC patients where some authors reported a median survival drop from 6.4 years in recurrence-free patients to 3.5 years in those with recurrence [9]. Recurrence influences both the 5-year and the disease-free survival in OSCC patients [8]. Of the resection cases in our study, 11.7% had histologically-proven recurrence, 47.6% were recurrence-free after ≥ 3 years of follow-up, and 40.8% had unknown recurrence (lost follow-up before reaching the 3-year milestone).
Statistical analysis yielded no significant association between local recurrence and each of tumor site, age group, T- and N-stage. This can be attributed to the limited number of cases with local recurrence and the significant portion of patients who lost follow-up.
The study has limitations. Better data quality about survival would have been beneficial. Smoking history and recreational habits (e.g., tobacco chewing) were not regularly documented, which would have been useful in investigating possible risk factors. A major challenge was the loss of follow-up, due to the mobile expat nature of the population in Qatar, with high losses to follow-up due to relocation. Nevertheless, the study has important strengths. There is no published data about OSCC for the State of Qatar, despite its ethnically diverse population. We employing a generous sample (154 patients) and examined a wide range of demographic, clinical, epidemiological, histopathological and surgical parameters. Our sample is representative of all cases in the country as our center is the sole reference center in Qatar that reviews all OSCC cases of all stages involving any location of the oral cavity.