This is the first study evaluating population-based cancer survival in the Kingdom of Saudi Arabia. The study reports the 5-year observed survival for Saudi patients diagnosed with different cancers in the period from 2005–2009. It also examined the difference in the survival according to age, sex, disease stage, province, and the temporal trend over a 15-year period.
The 5-year observed survival for all cancers studied combined in the period from 2005–2009 was 66%. In general, most registries, report 5-year age standardized relative survival. Unfortunately, the required data to calculate this was not available for Saudi Arabia; hence, we are reporting 5- year observed survival.
Thyroid cancer had the best survival rate among solid tumors, similar to most reported registries. Thyroid cancer represents the second most common cancer in females and the third in the population in Saudi Arabia in the years reported [2, 3]. Breast cancer represents the commonest cancer in Saudi females and in population in general. Despite a 5-year observed survival of 72%, this represents a slightly lower value than western countries [4]. Reasons behind a lower survival are likely related to a relatively high percentage of presentation in advanced stage (12.5%) and low rate of screening [5]. Screening for breast cancer has developed in several phases yet has not materialized into a national screening program [6–9]. Several opportunistic screening campaigns took place in several cities of Saudi Arabia mostly by non-governmental organizations [9]. Uterine cancer is generally related to nulliparity[10], which is uncommon is the Saudi population. 5-year observed survival is similar to other western countries [4]. Urinary bladder cancer is seen mostly in males with 84.4% of diagnosed cases in our study of male sex. Despite 10.7% of the patients studied being in metastatic stage, which is around double what is seen in the USA [11], the 5-year observed survival of 59% was similar to western reports [4]. Colorectal cancer represents the commonest cancer in Saudi males and the second in the whole population [3]. The 5-year observed survival was remarkably similar to western data despite the latter representing cancer-specific survival. SEER data reported 54.8 and 57.7% 5-year cancer specific survival for colorectal cancer between 1990–1994 for males and females, respectively. This figure improved with a hazard ratio for improvement of 0.70 (95% confidence internal 0.68–0.72) for the years 2004–2009 in white Americans [12]. Evidently, a major factor affecting our survival figures in colorectal cancer is the late presentation in Saudi population with 30% of our patients presenting in metastatic stage. In fact, data on colorectal screening rates in a sample of the Saudi population showed 5.6% screening rate with less than 1% utilizing colonoscopy [13].
Prostate cancer incidence is surprisingly low in Saudi Arabia with age-standardized rate (ASR) of 6.3/100,000 in 2016 [2]. This in contrast to a much higher reported incidence in USA and UK with ASR of 109 and 170 per 100,000 respectively[14, 15]. The reason for the low incidence may relate to it being secondary to the lack of PSA screening [16]. This might also be the reason for a higher incidence of advanced stage at presentation with 32% being metastatic at presentation and the lower 5-year observed survival of 49%.
Liver cancer typically develops in patients with liver cirrhosis. The prevalence of hepatitis B infection in Saudi patients diagnosed with hepatocellular carcinoma (HCC) was reported to be 67% (95% CI: 57.7–75.3), with a much lower incidence of 11.9 for Hepatitis C virus [17]. Screening plays an important role in the detection of early stage HCC, which might make it more amenable for curative surgery [18]. Despite the implementation of a national vaccination program for hepatitis virus in 1989 in Saudi Arabia, the effect is not yet evident. Additionally, unfortunately no systematic screening for HCC is present in patients with cirrhosis, and hence the low 5-year observed survival rate of 19%.
The hematological malignancies in Saudi Arabia have encouraging survival rates compared to western data [4]. Reasons behind this could be a usual early diagnosis in hematological malignancies and the available tertiary care centers that accept such cases promptly.
The survival difference by age has public health implications that need attention. In our study, younger patients did better in terms of survival similar to other countries. The exception was breast and prostate cancer, and both were not statistically significant [4, 12, 19, 20]. Only 5 patients were younger than 40 years of age with prostate cancer which is expected due to higher median age at diagnosis. Older patients tend to have lower survival that may be explained by other comorbidities competing for death and are less likely to get aggressive therapy [19].
In our study, sex has displayed a prognostic role with females having better survival across all reported cancer sites except in urinary bladder cancer where the difference was not statistically significant. It is important to note that urinary bladder cancer occurs predominantly in males in our region [2, 3]. The survival superiority for females in cancer has been previously described in many populations in the literature [4, 19, 21]. Many hypotheses were proposed, of which that sex hormone patterns in female could play a role in providing a superior survival in females compared to males [4].
Cancer stage at diagnosis serves as one of the most important prognostic factors in generally all cancer sites. Patients with localized disease have an advantage in survival compared with locally advanced and metastatic disease in view of the possible surgical intervention. The staging system used in our study represents the one used by the CanReg-4 registry program supplied by IARC. We interpret our survival data with caution in view of the high number of unknown cancer stage in some sites. The lower survival seen in some cancers like stomach, lung and liver represent the usually advanced stage in which they present. In general, cancers which are known to have higher sensitivity to systemic therapies in advanced stages had markedly improved 5-year observed survival such as thyroid, Hodgkin’s and non-Hodgkin’s lymphoma.
Survival trends observed in our study confirmed the steady improvement in the 5-year observed survival over time. Lung and uterine cancer survival rates did plateau over the 15-year period studied. Hodgkin’s lymphoma had an excellent survival rate of 86% in the period 1994–1999 and this was maintained in the years 2005–2009. These survival trends need to be interpreted with caution as many factors might have played a role like health care accessibility, care quality, staff expertise, treatment availability and statistical artifacts [19]. One important factor is the continued improvement in anticancer therapy. Additionally, the health care system has advanced with time. This might be behind the improvement in the 5-year observed survival over time.
Survival results from the Northern province underperformed other provinces in the Kingdom of Saudi Arabia. This could be explained by lack of oncology centers and patient education in that province. Acknowledging these defects helps to tackle these issues leading to improvement in survival.
Population-based survival may give an insight into the effectiveness of the health care system in managing cancer patients [19]. Achieving better cancer control is a global health challenge that is used as a tool to assess the health care system efficacy and helps as guide if improvement is required by comparing population survival rates with others. The CONCORD-3 study is one of the biggest global comparative studies with 322 separate registries in 71 countries covering approximately 1 billion people of the global population. It investigated patients diagnosed with cancer between 2000–2014 and has shown that survival trends were in general on an upwards trend. However, it was clear that high-income countries enjoy better survival than low-middle income countries [22].
As the population in Saudi Arabia continues to grow, the incidence of cancer has increased from 1990 to 2016 [23]. The SCR is the first national registry in Saudi Arabia established in 1992 by a resolution of the Minister of Health. It is one of first registries founded in the region. However, clearly efforts are needed to improve the registration process to get a more comprehensive survival and mortality data in the future.
Comparative survival results between populations and countries help health care officials to identify issues with the current health care system and possibly formulate national cancer strategies to improve cancer control [22, 24]. The need for a national cancer screening programs in Saudi Arabia should be carefully studied. This is because the incidence of cancer in general in Saudi Arabia is much below western levels and the benefit of mass screening is not known.
Our study has several limitations. First, only 54% of cancer cases submitted were analyzed as the required data was not available for the others. On the other hand, this percentage likely represents one of the highest reported survival studies on a national level. An additional limitation was our inability to produce relative survival rates in view of the lack of the denominator data.
In summary, the relatively lower observed survival in some solid tumors may represent the advanced stage at presentation. Hematological malignancies have 5-year observed survival comparable to the developed countries. A positive trend in cancer survival over time was seen in most cancers. The Saudi cancer registry needs to develop a systematic method for capturing mortality and survival data with time. This study highlights the need for future studies assessing the role of screening programs for early diagnosis which could lead to improving the overall survival of cancer in the Kingdom of Saudi Arabia.