Global Trends in Ovarian Cancer Incidence Highlight Regional, Histological Variations

Variations in global patterns and trends of ovarian cancer (OC) incidence and its subtypes were observed between 1988 and 2017, with potential influence from genetic and reproductive factors, according to a study published in eClinicalMedicine.¹

Despite declining OC incidence rates over the past few decades, particularly in high-income countries, OC prognosis remains dismal, with age-standardized 5-year net survival rates varying between 30% and 50% in most countries.² However, only 3 studies have investigated the global patterns or trends of OC incidence, both overall and by histological subtype.¹

Due to the limited scope of these studies and the changes in OC diagnostic techniques and risk factors, the researchers of the present analysis stressed the need for up-to-date comprehensive epidemiological data on global patterns and trends of OC incidence and its histological subtypes. They aimed to provide this update by computing annual percent changes (APCs) to describe global trends in age-standardized rates (ASRs) of OC and its subtypes. They also calculated the proportions of ASR for each subtype relative to the ASR of OC for individual countries.

Between 1988 and 2017, there were significant global variations and trends in ovarian cancer incidence and its subtypes. | Image Credit: flashmovie - stock.adobe.com

To do so, the researchers extracted all data from the most recent entry into the Cancer Incidence in 5 Continents database (C15 Volume XII) and the C15plus database. Published every 5 years since the 1960s by regional and national cancer registries worldwide, the C15 series contains high-quality information on new cancer cases by site, registry, sex, 5-year age group, and histology (if available), together with age-specific populations.

They obtained historical data (1988-2012) from the C15plus database and the most recent data (2013-2017) from the C15 database. Based on available registries in the C15 Volume XII database, international patterns for OC incidence and its histological subtypes were described by country, world region, and human development index (HDI) from 2013 through 2017.

The HDI is based on 3 fundamental characteristics of human development: being knowledgeable, having a long and healthy life, and having a decent standard of living. Based on their HDI values between 2013 and 2017, countries were divided into 4 groups (very high, high, medium, and low) to examine the patterns of OC incidence vs human development.

International trends of OC incidence and its histological subtypes also were calculated every 5 years between 1988 and 2017. Eligible countries were included in C15 Volume XII and had at least 15 consecutive years of data. Therefore, 65 and 40 countries from 5 continents were eligible for pattern description and trend analysis, respectively.

The researchers categorized the world regions as Africa, Asia, North America, South America, Eastern Europe, Western Europe, Southern Europe, Northern Europe, Central Europe, and Oceania. Also, they categorized the OC histology subtypes as serous carcinoma, endometrioid carcinoma, mucinous carcinoma, clear cell carcinoma, adenocarcinoma not otherwise specified (NOS), other epithelial OC (EOC), germ cell tumor (GCT), sex cord-stromal tumor (SCST), and other tumors.

In the most recent period (2013-2017), the researchers detected the highest ASRs of OC in Eastern Europe, followed by Central and Southern Europe. More specifically, the highest ASRs occurred in Latvia (15.53 per 100,000 person-years) and Lithuania (13.28 per 100,000 person-years). Conversely, they detected the lowest ASRs in Africa and Asia, with the lowest recorded in Benin (3.26 per 100,000 person-years).

Also, the highest ASR occurred in very high HDI regions (8.22 per 100,000 person-years), while the lowest ASR was seen in areas with medium HDI values (5.52 per 100,000 person-years).

As for OC incidence trends, significant decreases in ASRs were found in 19 of 40 countries between 1988 and 2017, with the APC ranging from −0.46 to −2.87. Within all countries examined in Northern Europe, Western Europe, and Oceania, ASRs decreased from high to intermediate rates. The largest declines occurred in Iceland (APC, −2.87; 95% CI, −4.80 to −0.90), the Netherlands (APC, −1.75; 95% CI, −2.86 to −0.63), and New Zealand (APC, −1.66; 95% CI, −2.35 to −0.96).

Similarly, the ASRs in Eastern Europe, North America, and South America steadily decreased, with substantial reductions in Estonia (APC, −0.56; 95% CI, −1.04 to −0.09), Canada (APC, −0.80; 95% CI, −1.03 to −0.56), the US (APC, −1.47; 95% CI, −1.71 to −1.23), and Colombia (APC, −1.00; 95% CI, −1.91 to −0.08).

As for Southern and Central Europe, some countries maintained a steady trend while others experienced significant declines. The researchers observed noteworthy decreases in Austria (APC, −2.40; 95% CI, −3.22 to −1.57), Germany (APC, −1.15; 95% CI, −1.93 to −0.37), and Switzerland (APC, −1.22; 95% CI, −1.58 to −0.86). Although most Asian regions exhibited stable temporal trends, several countries, like Japan (APC, 1.90; 95% CI, 1.32-2.50) and South Korea (APC, 1.18; 95% CI, 0.82-1.53), showed significant upward trends.

In terms of OC histological subtypes, serous carcinomas consistently exhibited the highest ASRs among most countries assessed, especially in Europe; Lithuania recorded the highest ASR at 6.59 per 100,000 person-years. However, the ASRs of mucinous carcinomas were particularly high the Asian countries of Brunei (2.59 per 100,000 person-years), the Philippines (1.12 per 100,000 person-years), and Singapore (1.12 per 100,000 person-years); Asian regions also had higher ASRs of endometrioid and clear cell carcinomas.

Globally, serous carcinomas constituted 37.66% of the total OC ASR, followed by other tumors (13.17%), adenocarcinoma NOS (12.77%), other EOC (8.64%), endometrioid carcinomas (7.76%), mucinous carcinomas (7.00%), clear cell carcinomas (5.94%), GCT (4.78%, and SCST (2.25%).

The researchers acknowledged their study’s limitations, including the absence of national cancer registries in several countries. Consequently, they combined regional cancer registries to approximate the national profiles of these countries; this may have resulted in relative underrepresentation. Despite their limitations, the researchers suggested areas for further research based on their findings.

“Further research is necessary to definitively identify the specific factors driving these variations in OC incidence across different countries, ultimately enabling the development of region-specific prevention and control strategies to effectively mitigate the global burden of this disease,” the authors concluded.

References

1. Wei YF, Ning L, Xu YL, et al. Worldwide patterns and trends in ovarian cancer incidence by histological subtype: a population-based analysis from 1988 to 2017. EClinicalMedicine. 2024;79:102983. doi:10.1016/j.eclinm.2024.102983

2. Allemani C, Matsuda T, Di Carlo V, et al. Global surveillance of trends in cancer survival 2000-14 (CONCORD-3): analysis of individual records for 37,513,025 patients diagnosed with one of 18 cancers from 322 population-based registries in 71 countries. Lancet. 2018;391(10125):1023-1075. doi:10.1016/S0140-6736(17)33326-3