Chapter 24: Cancer survival in Singapore, 1993-1997

Chia KS

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Abstract

The Singapore cancer registry is a national registry established in 1968. Cancer registration is done by passive methods. The registry contributed survival data on 45 cancer sites or types registered during 1993–1997. Data on 34 cancers registered during 1968–1997 were utilized for survival trend by period and cohort approaches. Follow-up was done by passive methods, with median follow-up ranging between 2–72 months for different cancers. The proportion with histologically verified diagnosis for various cancers ranged between 27–100%; death certificates only (DCOs) comprised 0–7%; 76–100% of total registered cases were included for the survival analysis. The top-ranking cancers on 5-year age-standardized relative survival rates were non-melanoma skin (96%), thyroid (90%), testis (88%), corpus uteri (77%), breast (74%), Hodgkin lymphoma (73%) and penis (70%). Five-year relative survival by age group showed either a decreasing trend with increasing age groups or was fluctuating. Localized stage of disease ranged between 18–65% for various cancers and survival decreased with increasing extent of disease. Period survival closely predicted survival experience of cancers diagnosed in that period, and an increasing trend in period survival over different periods indicated an improved prognosis for cancers diagnosed in those calendar periods.


Singapore cancer registry

The Singapore cancer registry is a national registry established in 1968 to obtain information on cancer patterns in the entire country. The registry has been contributing data to the quinquennial IARC publication Cancer Incidence in Five Continents since Vol III[1]. Cancer notification is voluntary, and registration of cases is predominantly by passive methods with no personal contact with cases. The principal sources of information on incident cancer cases are the notification forms from all sections of the medical profession, pathology and hospital records[2]. The registry caters to a population of about 4.1 million with a sex ratio of 986 females to 1000 males in 2002, comprising major ethnic groups of Chinese, Malays and Indians. The average annual age-standardized incidence rate of all cancers and ethnic populations together is 235 per 100 000 among males and 200 per 100 000 among females in 1998–1999[3].

Map. Map showing location of Singapore

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The registry contributed data on survival from 45 cancer sites or types for the first time in this volume of the IARC publication on Cancer Survival in Africa, Asia, the Caribbean and Central America. In the present volume, the main tables pertain to the period 1993–1997. The data on survival for the years 1968–1992 are also utilized to elicit the trend in cancer survival using different approaches.

Data quality indices

The proportion of cases with histologically verified cancer diagnosis in the series varied from 100% for many cancers to 27% in liver cancer. The frequency of cases registered based on a death certificate only range between nil among many cancers to 7% in unspecified leukaemia. Cases excluded from the study, due to lack of follow-up and other basic information, are in the range of 0% for mesothelioma and 34% for bone cancers. Thus, 76–100% of the total cases registered are included in the estimation of the survival probability.

Table 1. Data quality indices - Proportion (%) of histologically verified and death certificate only cases, number and proportion of included and excluded cases by site, Singapore, 1993–1997 cases followed-up until 2001

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Outcome of follow-up

The follow-up of cases has been completely carried out by passive methods. Since certification of death is virtually complete, the cancer mortality information received from the death certificate is matched with the incident cancer database. The vital status of the unmatched incident case is then collected by scrutiny of hospital records, and all such cases are presumed to be alive until the end of the calendar year for which the mortality data are fully available.

The closing date of follow-up was 31st December 2001. The median follow-up ranged from 2 months for liver cancer and unspecified leukaemia to 72 months for testicular cancer. The completeness of follow-up at 5 years from the incidence date was 100% for all cancers as there are no losses to follow-up.

Table 2. Number and proportion of cases by vital status and median follow-up (in months) by site, Singapore, 1993–1997 cases followed-up until 2001

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Survival statistics

All ages and both sexes together

The top-ranking cancers on 5-year relative survival are non-melanoma skin (96%), thyroid (90%), testis (87%), corpus uteri (81%) and breast (76%). The lowest survival rate is encountered with cancer of the pancreas (4%), preceded by cancer of the liver (5%), oesophagus (6%) and lung (7%) and mesothelioma (9%). Salivary gland (69%) among other head and neck cancers and colon and rectum (50%) among gastrointestinal cancers have a higher survival rate than others in the category. Hodgkin lymphoma has a better survival rate than non-Hodgkin. The survival figures for haematopoietic malignancies are as follows: multiple myeloma (19%), lymphoid leukaemia (46%), myeloid leukaemia (18%) and unspecified leukaemia (9%).

The 5-year age-standardized relative survival (ASRS) probability for all ages together is observed to be less than or similar to the corresponding unadjusted one for a majority of cancers. Also, the 5-year ASRS (0–74 years of age) is generally higher than or similar to the corresponding ASRS (all ages) for a majority of cancers.

Table 3. Comparison of 1-, 3- and 5-year absolute and relative survival and 5-year age-standardized relative survival (ASRS) by site, Comparison of 1-, 3- and 5-year absolute and relative survival and 5-year age-standardized relative survival (ASRS) by site

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Figure 1a. Top ten cancers (ranked by survival), Singapore, 1993–1997

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Sex

Table 4a. Site-wise number of cases, 5-year absolute and relative survival by sex, Singapore, 1993–1997 cases followed-up until 2001

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Male

The 5-year relative survival of cancer of the testis is 87%, prostate is 63% and penis is 66%. Cancers of the hypopharynx, breast, small intestine and urinary bladder have a notably higher survival among males than females.

Figure 1b. Top five cancers (ranked by survival), Male, Singapore, 1993–1997

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Female

The 5-year relative survival from cancers of the breast, uterine cervix, ovary and vulva are 76%, 63%, 64% and 62%, respectively. Survival is markedly higher among females than males in most cancers of the head and neck, rectum, anus, other thoracic organs, melanoma and non-melanoma skin, renal pelvis, Hodgkin and non-Hodgkin lymphoma and lymphoid leukaemia.

Figure 1c. Top five cancers (ranked by survival), Female, Singapore, 1993–1997

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Age group

The 5-year relative survival by age group reveals no distinct pattern or trend, and fluctuates with increasing age groups for most cancers. However, an inverse relationship between age group and survival was observed for cancers of the salivary gland, gallbladder, larynx, other thoracic organs, mesothelioma, corpus uteri, ovary, brain, thyroid and myeloid leukaemia.

Table 4b. Site-wise number of cases, 5-year absolute and relative survival by age group, Singapore, 1993–1997 cases followed-up until 2001

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Extent of disease

The information on the clinical extent of disease is analysed for selected cancer sites. Most of the cancers have been diagnosed at a localized stage ranging between 18–65% for various cancers. Nasopharyngeal cancer is an exception wherein a majority (36%) have regional spread of disease at diagnosis. Distant metastasis at diagnosis vary from 20% for ovarian cancer to 1% in cancer of the oral cavity. The unknown category is substantial, ranging between 24–50%. Survival is the highest among localized cancers, followed by regional and distant metastasis cases among the known categories.

Table 5. Proportion (%) of cases and 5-year absolute survival by extent of disease and site, Singapore, 1993–1997

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Figure 2a-2i. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997

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Figure 2a. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the tongue

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Figure 2b. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the oral cavity

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Figure 2c. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the nasopharynx

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Figure 2d. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the colon

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Figure 2e. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the rectum

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Figure 2f. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the larynx

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Figure 2g. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the breast

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Figure 2h. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the cervix

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Figure 2i. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the corpus uteri

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Figure 2j. Absolute survival from selected cancers by extent of disease : Singapore, 1993–1997: Cancer of the ovary

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Trend

The trend of survival data, estimated by the same method of semi-complete analytic approach as in the previous tables, is available for 34 cancer sites or types spanning 10 years in two time periods, 1988–1992 and 1993–1997. An increasing trend with an absolute difference of 8–10% and more between the two calendar periods is observed in cancers of the colon, rectum, larynx, non-melanoma skin, prostate and urinary bladder. The survival was similar for a majority of other cancers in successive calendar periods.

Table 6. Comparison of 5-year absolute and relative survival of cases diagnosed between 1988–1992 and 1993–1997, Singapore

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Trend of survival by period and cohort approaches

The availability of data on registration and follow-up together for both a long (from the calendar year 1968) and up to a recent period (year 1997) of calendar time led to the possibility of estimating up-to-date survival and trend by period approach. Survival is also estimated by cohort approach for comparison.

Table 7. Number of cases by cancer site and calendar period, Singapore Cancer Registry, 1968–1997

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Table 8. Up-to-date 5-year relative survival estimates using cohort and period approaches by site and calendar period, Singapore, 1968–1997 cases followed-up until 1997

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Table 9. Up-to-date 10- and 15-year relative survival estimates using cohort and period approaches by site and calendar period, Singapore, 1968–1997 cases followed-up until 1997

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Figure 3a-3f. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore

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Figure 3a. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the breast

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Figure 3b. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the colon

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Figure 3c. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the non-melanoma skin

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Figure 3d. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the rectum

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Figure 3e. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the non Hodgkin lymphoma

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Figure 3f. Up-to-date 5-year relative survival of selected cancers by period and cohort appoaches, Singapore: Cancer of the cervix

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The 5-, 10- and 15-year relative survival estimates by cohort and period approaches are estimated for the different 5-year calendar periods from 1973–1977 to 1993–1997. A distinct correspondence between the two approaches is forthcoming. The period survival estimates at 5, 10 and 15 years of follow-up in a calendar period are seen to resemble the cohort survival estimates of the succeeding calendar periods after 5, 10 and 15 years respectively for most cancers. Thus, period survival closely predicts the survival experience of cancer cases diagnosed in that period. An increasing trend of period survival estimates over the different calendar periods is an indicator for improved prognosis for cancers diagnosed in those calendar periods.


References

  1. Parkin DM, Whelan SL, Ferlay J and Storm H. Cancer Incidence in Five Continents, Vol I to VIII: IARC Cancerbase No. 7. IARCPress, Lyon, 2005.
    (link to CI5)

  2. Lee HP, Day NE and Shanmugaratnam K. Cancer incidence in Singapore 1968–1982. IARC Scientific Publications No. 91. National University of Singapore, Singapore, 1988.

  3. Chia KS, Lee JJ, Wong JL, Gao W, Lee HP, Shanmugaratnam K. Cancer incidence in Singapore, 1998 to 1999. Ann Acad Med Singapore. 2002; 31(6): 745–50.