Glossary

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A

A	Age Class / Age Group In HKCaR, two types of age groups are generally used for cancer statistics: Board, the population is classified into 4 age groups: 0-19, 20-44, 45-64 and 65+ years; Quinquennial (5 year's interval), the population is classified into 18 age groups: 0-4, 5-9, 10-14, ... , 80-84, and 85+ years. And, three types of age groups are applied for Children and Adolescents due to different cut-off ages: Type 1 (Age range: 0-14 years), the population is classified into 4 age groups: 0, 1-4, 5-9 and 10-14 years; Type 2 (Age range: 0-18 years), the population is classified into 5 age groups: 0, 1-4, 5-9, 10-14 and 15-18 years; Type 3 (Age range: 0-19 years), the population is classified into 5 age groups: 0, 1-4, 5-9, 10-14 and 15-19 years.
A	Age-specific Rate The age specific rate (a_i, per 100,000 population) is a ratio of the event for the specific age group i. It is calculated by dividing the number of cases in the age class i (r_i) by the corresponding population-at-risk (n_i) and multiplying the result by 100,000. Thus, a_i = r_i / n_i × 100,000
A	Age-standardised Rate Standardisation is necessary when comparing several populations with different age structures or for the same population over time in which the age profiles change accordingly. Comparisons with rates from other sources are valid only if they use the same standard population for calculations. The age-standardised rate (ASR, per 100,000 population) in accordance with direct method is calculated by summing up the products of the age-specific rates (a_i, where i denotes the i^th age class) and the number of persons (or weight) (w_i) in the same age subgroup i of the chosen reference Standard Population, then dividing the sum of Standard Population weights, i.e. ASR = Σa_iw_i / Σw_i × 100,000 Cases of cancer of unknown age may be included in a series. An adjustment is made by multiplying the derived ASR by R / Σr_i where R denotes the total number of cases; A denotes the number of age groups; Σr_i = r₁ + r₂ + r₃ + ··· + r_A, where r_i denotes the number of cases occurred in the i^th age class;
A	Average Annual Percent Change Average Annual Percent Change (AAPC)¹ is a summary measure of the trend over a specified interval. It is computed as a weighted average of the annual percent changes over a period of years from the joinpoint regression model². HKCaR adopts at least the past 25 years of available data to estimate the AAPC of age standardised rate over the past ten years. In view of the data quality and sufficiency, except the figures published during 2009-2014, data from 1983 to 1990 are generally not included for estimation. For details of calculation, please refer to the website of National Cancer Institute. References: Clegg LX, Hankey BF, Tiwari R, Feuer EJ, Edwards BK. Estimating average annual percent change in trend analysis. Statistics in Medicine 2009; 28(29): 3670-82. Kim HJ, Fay MP, Feuer EJ, Midthune DN. "Permutation tests for joinpoint regression with applications to cancer rates" Statistics in Medicine 2000; 19:335-351: (correction: 2001;20:655).

C

C	Carcinoma in-situ Carcinoma in-situ (Ca in-situ) is non-invasive and the earliest form of cancer. Abnormal cells are present but have not spread to surrounding tissues or other parts of the body. (Note: The cancer incidence and mortality published in the HKCaR website DO NOT include the cases of carcinoma in-situ.)
C	Crude Rate The crude rate (C, per 100,000 population) is the ratio of the number of people in which the event happens in a specific time period to the population-at-risk. It is calculated by dividing the total number of cases (R) by the total number of population-at-risk (N) and multiplying the result by 100,000 for common interpretation, i.e. C = R / N × 100,000
C	Cumulative Rate The cumulative rate (CR%, unit: %) is the sum over each year of the age-specific incidence rates. It can be interpreted as an approximation of cumulative risk. The cumulative rate can be expressed as CR% = 100 × Σa_it_i where a_i is the age-specific incidence rate in the i^th age class, t_i is the width of the i^th age class, and the sum is until age class A. Assuming five-year age classes have been used in the calculation, the cumulative rate for age 0-74 can be expressed as CR%74 = 100 × Σ5a_i This calculation is theoretical and assumes that no death occurs in the period, and that age-specific incidence rates will be stable for an individual. For illustration of the calculation, please refer to "Chapter 11 Statistical methods for registries, P.Boyle and D.M. Parkin, International Agency for Research on Cancer".
C	Cumulative Risk The cumulative risk (or lifetime risk, unit: %) refers to the risk an individual would have of developing or dying from a particular cancer over his life span in the absence of any other cause of death. It can be expressed as Cum. Risk = 100 × [1 - exp (- CR% / 100)] For illustration of the calculation, please refer to "Chapter 11 Statistical methods for registries, P.Boyle and D.M. Parkin, International Agency for Research on Cancer".
C	Cytology Cytology refers to diagnosis is determined by examining the cells under a microscope.

D

DCO%

DCO%, one of the common quality indicators for assessing data completeness, is the percentage of cases which the information came from death certificate only. A high DCO% implies high proportion of incomplete case ascertainment due to failure to capture cases while patients are alive. (See also MV%)

Graphs of Data Quality Indicators

H

H	Histology Histology refers to diagnosis is determined by examining the histological characteristics of tissues or cells under a microscope, whilst the histology of a cancer refers to the microscopic characteristics of a tumour.

I

I	International Classification of Diseases (ICD) International Classification of Diseases (ICD) compiled by World Health Organization (WHO) is used to classify diseases and code diagnoses. In Hong Kong, ICD-9 (the 9th Revision of ICD) and ICD-10 (the 10th Revision of ICD) are commonly used to code malignant cancer cases. For the sake of consistency, those primarily based on ICD-9 are converted to grouped ICD-10 codes. ICD codes search
I	International Classification of Diseases for Oncology (ICD-O) International Classification of Diseases for Oncology (ICD-O) compiled by World Health Organization (WHO) is a dual-axial classification, with coding systems for both topography and morphology. It is principally used in cancer registries and pathology reports.
I	Incidence Cancer incidence is the number of new cancer cases arising in a specified population over a given time period. It can be either expressed as an absolute number of cases per year or as a rate per 100,000 persons per year.

M

M	Male : Female ratio The sex ratio is the number of males for each female in a population. A ratio above 1 means there are more males than females; for instance, a ratio of 1.23:1 means there are 1.23 males for every 1 female. A ratio of 1 means the numbers of males and females are equal. A ratio below 1 means there are more females than males; for instance, a ratio of 0.88:1 means there is 0.88 male for every 1 female.
M	Median age Median age is the age at the mid-point when the individuals are ranked by their age.
M	Morphology The morphology of a cancer refers to the histology and biological behavior of a tumour.
M	Mortality Cancer mortality is the number of cancer deaths occurring in a specified population over a given time period. It can be either expressed as an absolute number of deaths per year or as a rate per 100,000 persons per year.
M	Mortality-to-Incidence ratio The Mortality-to-Incidence ratio (MIR) serves as a population-based indicator to evaluate disparities in cancer screening, incidence, treatment, and survival. It is defined as the age-standardised mortality rate divided by the age-standardised incidence rate. i.e. MIR = ASR_mortality / ASR_incidence
M	MV% Morphological verification refers to cases for which the diagnosis is based on histology or cytology. MV%, one of the common quality indicators for assessing data completeness, is the percentage of cases with a morphologically verified diagnosis. Higher the MV%, higher the accuracy of diagnosis. (See also DCO%) Graphs of Data Quality Indicators

P

Population-at-risk (also known as person-years at risk)

Population-at-risk is the population that is exposed to the occurrence of an event (e.g. developing or dying from cancer) over a given time period. Generally, the population estimates are used to approximate the population at risk. The Hong Kong Cancer Registry adopts the mid-year population estimates provided by the government's Census and Statistics Department for this quantity.

Prevalence

The prevalence of cancer is an estimate of the number (or proportion) of people who have been diagnosed with cancer and are still alive at a specific point in time.

S

Stage

Cancer staging provides information about the extent of disease spread, usually classified as Stage I to IV or Unstaged. The classification of staging is primarily based on the American Joint Committee on Cancer (AJCC) and Union for International Cancer Control (UICC) TNM staging system for most cancer sites. The HKCaR only records stage at diagnosis for invasive cancers.

In general, an overall stage of 0, I, II, III and IV can be assigned for most cancers according to the combination of T (describes the size of tumour), N (describes whether the tumour has invaded to the nearby lymph nodes) and M (describes whether the tumour has metastasized to other parts of the body):

Stage 0 describes carcinoma in-situ in which abnormal cells are present;
Stage I, also known as early-stage cancer, indicates a tumour is present but it has not grown into nearby tissues and has not spread to the lymph nodes or other parts of the body;
Stage II indicates larger tumours have grown deeply into nearby tissues, which may have also spread to lymph nodes but no other parts of the body;
Stage III indicates larger tumours have grown deeply into nearby tissues, which have also spread to lymph nodes and other parts of the body;
Stage IV, also known as advanced-stage cancer, indicates the tumour has spread to distant parts of the body.

For detailed information on cancer staging, please refer to the website of AJCC or UICC.

Standard Population

Standard population is the age distribution used as weights to create age-adjusted statistics. The most widely used has been the World Standard population modified by Doll et al., (1966) from that proposed by Segi (1960).

The sum of standard population weights (w_i, where i denotes the i^th age class) is 1, i.e.

Sum of weights = Σw_i = 1 , where A = 18.

The table below shows various standard populations which have been used for age-adjusting in different countries.

Distribution of World Standard Populations (in percent)

Age Class index (i)	Age Group	Segi 1960 World Standard (Segi 1960)	New WHO World Standard (World 2000)	US Standard 2000 (US 2000)	European Standard 1976 (Euro 1976)	European Standard 2013 (Euro 2013)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18	0-4 5-9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85+	12.00 10.00 9.00 9.00 8.00 8.00 6.00 6.00 6.00 6.00 5.00 4.00 4.00 3.00 2.00 1.00 0.50 0.50	8.86 8.69 8.60 8.47 8.22 7.93 7.61 7.15 6.59 6.04 5.37 4.55 3.72 2.96 2.21 1.52 0.91 0.63	6.91 7.25 7.30 7.22 6.65 6.45 7.10 8.08 8.19 7.21 6.27 4.85 3.88 3.43 3.18 2.70 1.78 1.55	8.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 1.00	5.00 5.50 5.50 5.50 6.00 6.00 6.50 7.00 7.00 7.00 7.00 6.50 6.00 5.50 5.00 4.00 2.50 2.50
	All Ages	100	100	100	100	100

Survival rate

Cancer survival rate is the proportion of patients alive at some point subsequent to the diagnosis of their cancer. It is represented as the probability of a group of patients "surviving" a specified amount of time (E.g. 3 years, 5 years or 10 years).

T

T	Topography Topography is the site in the body where the tumour is located.