The situation of gynecological cancers in Thailand: incidence, histopathology, and survival outcomes from national cancer registry data

Abstract

Objective

Cervical, uterine, and ovarian cancers are the 3 main cancers of the female reproductive system. Analyzing data from the cancer registry database will help understand the situation and trends of these diseases.

Methods

This study utilized data from Thailand’s population-based cancer registries covering 16 provinces across 5 geographic regions between 2019 and 2021. Data collection included demographic characteristics, cancer incidence, histopathology, disease stage, and survival outcomes. Incidence rates were calculated using age-standardized rates (ASRs) per 100,000 population, and 5-year survival outcomes were compared across 2 time periods (2013–2017 vs. 2018–2022).

Results

During 2019–2021, Thailand recorded a mean annual ASR of 132.9 for females, with cervical cancer remaining the most common gynecologic cancer. The incidence of cervical cancer decreased from 19.5 per 100,000 in 1995–2000 to 10.3 per 100,000 in 2019–2021. Uterine cancer demonstrated a rising trend, from 3.6 per 100,000 in 2004–2006 to 6.1 per 100,000 in 2019–2021, while ovarian cancer incidence remained relatively stable at 5.9 per 100,000. Five-year survival rates improved significantly across all gynecologic cancers in 2018–2022 compared with 2013–2017. The hazard ratios for overall survival by stage ranged from 0.57 to 0.81 for cervical, 0.53 to 0.82 for uterine, and 0.57 to 0.81 for ovarian cancers (all p<0.05).

Conclusion

The incidence of cervical cancer in Thailand has declined over the past 2 decades, while the burdens of uterine and ovarian cancers are increasing. Five-year survival rates have significantly improved across all gynecologic cancer types.

INTRODUCTION

The National Cancer Institute of Thailand, under the Department of Medical Services which is part of the Ministry of Public Health, is the nation’s foremost leading cancer institute. The major tasks primarily involve cancer prevention, early detection, and treatment, and the institute is also responsible for the national cancer registry.

Thailand’s population-based cancer registry system began in 1986 in Chiang Mai province in the north of Thailand and has expanded to other provinces across 5 geographic regions. Data from these registries are consolidated and published in the book “Cancer in Thailand.” The latest edition, Volume XI (2019–2021), provides national estimates of cancer incidence by sex, geographic region, age group, and histopathology [1].

Over the years, the reported incidence of each cancer may have changed, partly reflecting the effectiveness of national cancer control efforts. This study focuses on gynecological cancers—cervical, uterine, and ovarian—analyzing national registry data to determine trends in incidence and survival, and to evaluate the impact of cancer control policies in Thailand. Additionally, this study examined patient survival rates over 2 time periods using data from a historical cancer registry to indicate trends in outcomes for gynecological cancer patients in Thailand.

MATERIALS AND METHODS

This was a population-based descriptive study using data from 16 provincial registries representing 5 geographic regions in Thailand between 2019 and 2021 (Fig. S1):

• 1. Northern region: Chiang Mai, Lampang, Lamphun, Nan.

• 2. Northeastern region: Khon Kaen, Ubon Ratchathani, Udon Thani.

• 3. Central region: Lopburi, Suphan Buri, Pathum Thani, Bangkok.

• 4. Eastern region: Chonburi, Rayong, Chanthaburi.

• 5. Southern region: Surat Thani, Songkhla.

Each regional registry collected data on all diagnosed invasive cancer cases, excluding carcinoma in situ. Follow-up was performed using both passive and active methods. Passive follow-up involved regular linkage with national death certificates and hospital databases, while active follow-up included direct review of medical records, telephone contact, and field verification by registry staff. Information was obtained from multiple sources, ensuring completeness of incidence and vital status data. The data collected for each cancer patient may slightly differ from one to another but must include:

• 1. Personal information: name, residential address, date of birth, age, and sex.

• 2. Cancer data: date and method of cancer diagnosis, type and primary site of cancer, histology and extent of cancer, and vital status of the patient.

  • 2.1. The primary site and histology of cancer were coded according to the International Classification of Diseases for Oncology (ICD-O) 3rd edition [2] and the current ICD-O 3rd edition, first revision [3].

  • 2.2. The incidence and the person-years at risk were obtained by pooling data of each hospital in the 5 regions. The expected incidence cases of the whole region were calculated by adjusting the pooled incidence cases by sex and age groups of the cancer registries of the whole region during 2019–2021 using the data from the Ministry of Public Health. The specific rates from expected cases in each region (excluding Bangkok) were calculated by age (5-year age group) and sex. The expected cases from the 5 regions and the actual cases in Bangkok were combined. We finally obtained the expected number of cases and estimated age-standardized rates (ASRs) for the whole Kingdom of Thailand for the period 2019–2021, based on sex and age group.

  • 2.3. The mortality rate was determined by the following methods. Registered cases were first matched with death certificates obtained from the Chief Medical Officer’s Offices, which were reviewed and matched with the registries’ incident case records. For cases without a match, data sources were revisited to gather additional information. Cases that could not be traced were classified as diagnosed only by death certificates. For all other cases, follow-up information was obtained through a review of hospital records, postal inquiries, and coordination with the healthcare system network.

This report presents the latest gynecological cancer data obtained from Thailand’s cancer registry and also analyzes and presents in-depth data from the Thai population database over various periods. Two- and 5-year survival data were analyzed across 2 intervals (2013–2017 and 2018–2022).

1. Definitions

• - ASR: incidence per 100,000 population, age-adjusted to the International Agency for Research on Cancer World Standard Population [4].

• - Survival rate: the proportion of patients alive after diagnosis, censored at death or last follow-up.

2. Statistical analysis

Incidence and ASRs were computed using registry data aggregated by age and region. Survival analysis employed the Kaplan-Meier method, and differences between periods were tested using the log-rank test. Statistical significance was defined as p<0.05. All statistical analyses were performed using Python version 3.10. The following libraries were utilized: pandas (version 1.5.3) for data manipulation and preprocessing, lifelines (version 0.28.0) for survival analysis and modeling, and matplotlib (version 3.7.0) for data visualization.

3. Ethical considerations

All data were anonymized in compliance with the Personal Data Protection Act B.E. 2562 (2019). The study was approved by the Ethics Committee of the National Cancer Institute of Thailand (Institutional Review Board No. EC68010), which waived individual patient consent due to the use of secondary data.

RESULTS

1. Cancers in Thailand

During the years 2019–2021, Thailand had a mean annual age-standardized cancer incidence rate (ASR per 100,000) of 137.6 for males and 132.9 for females. This accounted for a total of 140,789 new cancer patients, being 67,667 males and 73,122 females. Chiang Mai province had the highest incidence rate of cancer in both males and females. Table S1 shows the number of new cancer cases and the mean ASR by sex in Thailand and in each province with cancer registry.

Fig. S2 displays the top ten leading cancers in both males and females between 2019 and 2021. Among males, liver/bile duct cancer was the most common, followed by lung and colorectal cancers. For females, breast cancer was the most common, followed by colorectal and lung cancers.

2. Gynecologic cancers

Gynecological cancers are one of the significant issues in Thailand’s public health system, particularly cervical cancer, which is the leading cancer among Thai women. After the implementation of various measures, including the current availability of the cervical cancer vaccine and the national cervical cancer screening policy, the incidence of cervical cancer has continuously decreased. Regarding the other 2 gynecologic cancers, the incidence of ovarian cancer has remained stable over the years, whereas an increasing trend was observed for uterine cancer. Details of each gynecologic cancer by geographic region and province, age group, histopathology, stage of cancer, and survival by stage are as follows.

Cervical cancer

Cervical cancer has been the most common gynecological cancer in Thailand over the years. Nevertheless, its incidence had been decreasing. The ASR was 19.5 per 100,000 women from 1995 to 1997 and sequentially dropped to 10.3 per 100,000 women from 2019 to 2021 (Fig. 1).

Fig. 1. Incidence rate of cervical cancer in Thailand 1996–2020.

ASR, age-standardized rate.

The decline in cervical cancer incidence can be attributed to the implementation of Thailand’s national cervical cancer screening policy, introduced in 2005 and still ongoing. Under this policy, Thai women aged 30–60 years are eligible for free screening every 5 years. Furthermore, since 2020, we have enhanced the screening program by switching from Pap smears to the more effective primary human papillomavirus (HPV) test. The policy refers women with abnormal screening results for colposcopy and provides them with further treatment as needed [5].

Another key component of the national policy is the administration of the cervical cancer vaccine to fifth-grade elementary school students, a program implemented since 2017 and now extended to multi-cohort vaccination target groups. This vaccination initiative complements existing screening programs, with the goal of achieving the World Health Organization’s target of reducing cervical cancer incidence to fewer than 4 cases per 100,000 population by 2030 [6].

The incidence of cervical cancer was highest in the Northern and Eastern regions, with ASRs per 100,000 women being 12.9 and 12.8, respectively (Fig. S3). Regarding the age distribution, the common age groups were from 35-year-olds to 65-year-olds, with a slight decline afterwards (Fig. S4).

Squamous cell carcinoma was the dominating histology at approximately 70%, ranging from 62% to 75% (Fig. S5). Although squamous cell carcinoma was also found common in Bangkok, its percentage was lower at 62%, while adenocarcinoma accounted for 31%, which is higher than in other regions.

Despite incomplete data on cancer stage being encountered in different regions across Thailand, most cervical cancer patients in all areas were diagnosed when their cancer had regional extension (Fig. S6).

Two- and 5-year survival rates for cervical cancer are shown in Fig. 2. Across all stages, survival was higher in 2018–2022 compared with 2013–2017 (hazard ratio [HR] for stages I–IV: 0.574, 0.573, 0.689, and 0.811, respectively; p<0.001), regardless of treatment modality. This benefit is likely from more advanced technology with surgery, radiation, and cytotoxic agents in the modern era, as well as an increasing number of gynecologic oncologists and supported resources across the country [6].

Fig. 2. Survival analysis according to stage of cervical cancer in period 2018–2023 compared to 2013–2017.

CA, cancer.

Uterine cancer

From 2004 to 2015, uterine cancer was the third most common gynecologic cancer after cervical and ovarian cancers. While cervical cancer incidence decreased over the years, the incidence of uterine cancer increased during the same period. The ASR per 100,000 women was only 3.6 during 2004–2006, rising to approximately 4.0–4.5 between 2007 and 2015, and 6.7 and 6.1 during 2016–2018 and 2019–2021, respectively (Fig. 3).

Fig. 3. Incidence rate of corpus uteri cancer in Thailand 1996–2020.

ASR, age-standardized rate.

The regions with higher ASR than the national rate were the Eastern and Central regions, 7.4 and 6.8 per 100,000 women, respectively (Fig. S7).

The age incidence of uterine cancer exhibited a similar bell-shaped pattern across all regions. The incidence started rising from age 40 years, peaked around ages 55 years to 65 years, and declined thereafter (Fig. S8).

Endometrioid carcinoma was the main histology, approximately 62%, with a range of 41%–74% (Fig. S9).

Among the patients with data on uterine cancer stages, most had localized disease, while a smaller percentage had regional spread, and the smallest percentage had distant spread (Fig. S10).

Similarly, 2- and 5-year survival rates for uterine cancer are shown in Fig. 4. Across all stages, survival was higher in 2018–2022 compared with 2013–2017 (HR for stages I–IV: 0.620 [p<0.001], 0.528 [p=0.004], 0.691 [p=0.001], and 0.819 [p=0.040], respectively), also independent of treatment modality. The new treatment being used in the recent era, according to updated clinical practice guidelines and the greater number of practicing gynecologic oncologists, should influence better survival outcomes in the latter years [7].

Fig. 4. Survival analysis according to stage of corpus uteri cancer in period 2018–2023 compared to 2013–2017.

CA, cancer.

Ovarian cancer

The incidence of ovarian cancer in Thailand over the years seemed to be stable, approximately 5.6 to 6.0 per 100,000 women from 2005 to 2017 and 5.9 in 2019–2021 (Fig. 5). The incidence in different regions across the country seemed to be comparable, but it was highest in the Eastern region (Fig. S11).

Fig. 5. Incidence rate of ovarian cancer in Thailand 2005–2020.

ASR, age-standardized rate.

The age incidence of ovarian cancer in all regions had a similar pattern, rising after age 35 and peaking around 65 or 70 before declining (Fig. S12).

Serous carcinoma was the most common histopathology across the regions, ranging from 15% to 27% (Fig. S13). The rate of unknown-stage ovarian cancer was found to be up to 78% (Fig. S14), which was similar to that of uterine cancer. It is possible, for the same reasons as uterine cancer, that the accurate diagnosis of cancer has not been recorded by a gynecologic oncologist. Another possible reason was that some medical records regarding the cancer stage were not collected or completed in the cancer registry. Among those with a known extent of cancer, distant metastases were found to be rather higher than cervical and uterine cancer. These findings conformed with the natural history of ovarian cancer, which did not have any symptoms or had only vague abdominal symptoms, leading to widespread disease at diagnosis.

Comparable findings were observed for ovarian cancer, with 2- and 5-year survival rates presented in Fig. 6. Across all stages, survival was higher in 2018–2022 compared with 2013–2017 (HR for stages I–IV: 0.574, 0.573, 0.689, and 0.811, respectively; p<0.001), also regardless of treatment modality. Focusing on stage IV patients, only slight improvement was found. This finding may be due to the lack of support for treatment from the availability of new targeted therapies and/or immunotherapies. This situation is likely due to limited access to the newer drugs, which are often not included in the health coverage system for reimbursement [8].

Fig. 6. Survival analysis according to stage of ovarian cancer in period 2018–2023 compared to 2013–2017.

CA, cancer.

DISCUSSION

Gynecological cancers remain a significant public health issue in Thailand. Although the incidence of cervical cancer, the leading gynecological cancer, has been steadily declining for over 20 years due to various measures, including screening combined with HPV vaccination at the policy level, uterine and ovarian cancers pose increasing challenges. This trend aligns with the incidence in Western countries, where uterine cancer is the leading gynecological cancer in women (excluding breast cancer). Epidemiological data collection using hospital and population-based cancer registries allows Thailand to monitor the incidence trends and characteristics of each type of gynecological cancer, leading to systematic analysis of factors that may affect the development and progression of these diseases. This information can then be used to plan effective gynecological cancer management.

The strength of this study lies in the direct use of data from the Thai Cancer Registry database. The registry data were analyzed to determine incidence rates across different time periods and disease characteristics, such as pathological features, disease stage, and age range, separated by region in Thailand. Additionally, 5-year survival rates were studied and compared between patient data from 2 time periods, allowing us to understand that the outcomes of cancer treatment in Thailand have improved over time. But this study found that some parts of the cancer registry are incomplete, like the disease stage and pathological type. This missing data may require caution when analyzing factors like cancer survival rates. This highlights the need to further strengthen registry data systems for gynecologic cancers in Thailand.

The incidence of cervical cancer in Thailand has declined over the past 2 decades, while the burdens of uterine and ovarian cancers are increasing. Five-year survival rates have significantly improved across all gynecologic cancer types. These findings highlight the changing landscape of gynecologic cancers in Thailand and the importance of prevention and treatment strategies.

SUPPLEMENTARY MATERIALS

Table S1

Mean annual age-standardized incidence rate (ASR per 100,000), all sites, 2019–2021

Fig. S1

Thailand geographic regions and provinces having cancer registries.

Fig. S2

Top 10 cancers in Thailand in male and female between 2019–2021 (age-standardized rate per 100,000).

Fig. S3

Cervical cancer in different regions, mean annual rate per 100,000 (2019–2021).

Fig. S4

Age-specific incidence rates of cervical cancer, mean annual rate per 100,000 (2019–2021).

Fig. S5

Percentage distribution of histological types among microscopically verified cervical cancer (2019–2021).

Fig. S6

The percentage in stage distribution of cervical cancer (2019–2021).

Fig. S7

Corpus uteri cancer in different regions, mean annual rate per 100,000 (2019–2021).

Fig. S8

Age-specific incidence rates of corpus uteri cancer, mean annual rate per 100,000 (2019–2021).

Fig. S9

Percentage distribution of histological types among microscopically verified corpus uteri cancer (2019–2021).

Fig. S10

The percentage in stage distribution of corpus uteri cancer (2019–2021).

Fig. S11

Ovarian cancer in different regions, mean annual rate per 100,000 (2019–2021).

Fig. S12

Age-specific incidence rates of ovarian cancer, mean annual rate per 100,000 (2019–2021).

Fig. S13

Percentage distribution of histological types among microscopically verified ovarian cancer (2019–2021).

Fig. S14

The percentage in stage distribution of ovarian cancer (2019–2021).