Ovarian cancer rates in Singapore doubled over past 4 decades

The rates of ovarian cancer in Singapore have more than doubled over the past 40 years, with evidence of variation between the main ethnic groups, a recent study has shown.

Using the Singapore Cancer Registry, the incidence of ovarian cancer in Singapore between the years 1968 and 2012 was evaluated. The cases excluded teratomas, immature teratomas, and borderline, germ cell, and sex cord stromal tumours.

The results showed a doubling of the age-standardized incidence of ovarian cancer, from 5.8 per 100,000/year in the years 1968–1972 to 12.5 per 100,000/year in the years 2008–2012. [Asian Pac J Cancer Prev 2019;20:3563-3569]

While the incidence rates between 1968 and 2012 increased among the three main ethnic groups, the highest incidence in the years 2008–2012 was noted in Malays (14.0 per 100,000/year), followed by Chinese (12.5 per 100,000/year) and Indians (11.0 per 100,000/year).

The increased incidence applied to all the subtypes assessed – serous, clear cell, endometrioid, and mucinous. The greatest increase was noted in the most common subtype, serous carcinoma (from 0.4 [in 1968] to 3.4 per 100,000/year), while mucinous (from 1.3 to 2.7 per 100,000/year), clear cell (from 0.1 to 1.8 per 100,000/year), and endometrioid (from 0 to 1.5 per 100,000/year) exhibited more subtle increases. Among the ethnic groups, the incidence of mucinous carcinoma was less common in Indians, while clear cell carcinoma was less common in Malays and Indians.

The variation in incidence and subtype by ethnicity warrants further investigation “as these may offer clues to mechanisms of ovarian carcinogenesis,” said the researchers.

Conversely, the increased incidence of ovarian cancer did not appear to affect age-standardized mortality due to ovarian cancer with rates remaining relatively stable over the 40-year period, they said. This was reflected in the mortality rates which rose from 1.4 per 100,000/year in 1968–1972 to 3.8 per 100,000/year in 1978–1982, and then plateaued at 3.3 to 4.0 per 100,000/year from 1982 to 2012.

The mortality results suggest an improvement in survival rates, noted the researchers, with 5-year Age-Specific Relative Survival increasing from 29.2 percent in 1983–1987 to approximately 45 percent from 1993 onwards. [Singapore Cancer Registry (SCR), National Registry of Diseases Office, Ministry of Health, Singapore (2015)]

However, they pointed out that the improved survival was unlikely due to improved screening or awareness of the condition. For example, while about 50 percent of ovarian cancers were diagnosed at stage I or II (36 and 9 percent, respectively, in 2008–2010), serous carcinoma was often diagnosed at stage III or IV (58 and 24 percent, respectively, in 2008–2010). As such, the survival benefit is likely due to improvement in treatment, they said. The relatively frequent late-stage diagnosis of serous carcinoma calls for efforts to increase awareness among women regarding ovarian cancer symptoms, they added. 

There was also a notable decrease in total fertility rate (TFR), from 5.76 to 1.79 per female in the years 1960 and 1978, respectively, to 1.29 per female in 2012. This decrease affected all three ethnic groups, though TFR in 2012 was higher in Malay compared with Chinese and Indian women (1.69, 1.18, and 1.15 per female, respectively). “[However], our results suggest that known reproductive factors such as fertility, infertility, and oral contraceptive use do not completely explain [the] differences in incidence rates,” said the researchers.