3: Mortality & Survival

Question 1

What can measures of mortality & survival tell us?

Answer 1

Mortality: public heath & heathcare priorities, how big a problem is in a population
Survival; effectiveness of heathcare & cancer control

Question 2

What must be defined to measure cancer mortality?

Answer 2

Death
Population
Time period

Question 3

Give a few examples of different ways cancer mortality can be measured

Answer 3

• all cause deaths
• cancer specific deaths
• general population at risk
• cancer patient population

Question 4

How do you calculate all-cause mortality rate?

Answer 4

No. Of death (all causes) in population over time (t)
/
Total person-time at risk

Question 5

How do you calculate cancer specific mortality rate?

Answer 5

No. Of deaths (cancer specific) in population over time (t)
/
Total person-time at risk

Question 6

How do you calculate annual mortality rates?

Answer 6

No. Of deaths from cancer of interest in defined population in 1 year
/
Mid-year population in the same year

Question 7

T or F:
- cancer survival is calculated from cancer onset to death
- cancer survival can be used as a prognosis for individuals
- survival analysis is also known as ‘time-to-event’ analysis

Answer 7

• F: from cancer DIAGNOSIS to death
• F: it is not a prognosis, only an average
• T

Question 8

Describe the requirements in order to calculate survival anaylsis?

Answer 8

Well defined:
- case: eg cancer site, histology, stage, sex
- starting point: diagnosis, treatment, admission to hospital
- outcome: death (recurrence, treatment complication)

Question 9

What is the best way to display survival time graphically?

Answer 9

Showing by time since diagnosis is preferred over calendar year as it is easier to compare similar points in cancer natural history between patients

Question 10

How do you calculate the survival probability of a specific year?

Answer 10

Probability of survival = number of people alive in that year (given they have survived previous years) / total number of patients

Question 11

How do you calculate cumulative survival probabilities?

Answer 11

Calculate probability of survival in each consequetive years and multiply together

Question 12

On a Kaplan-Meier table, what is on the x and y-axes?

Answer 12

X: years
Y: survival probability

Question 13

Why are Kaplan-Meir tables often preferred over actuarial life tables?

Answer 13

They should a stepped line rather than survival curve
This means no values are estimated

Question 14

T or F:
- Kaplan-Meier graphs cannot compare 2 groups
- When comparing groups, the cumulative survival probability is the same for each group
- Groups are defined by sex, stage, histology, etc

Answer 14

• F: they can be used for comparisons
• F: survival probabilities are calculated separately
• T

Question 15

What is the advantages for cancer-specific survival?

Answer 15

• for overall survival, there is no distinction from cancer and other causes of death
• cancer-specific takes into account competing causes of death
• easier to understand the cancer-specific risk to patients

Question 16

How do you calculate relative/ net survival?

Answer 16

Observed survival in cancer patients
/
Expected survival in general population

Question 17

What is relative survival?

Answer 17

The survival adjusted for the probability of dying from other causes that aren’t;;t cancer-specific

Question 18

Use lung cancer in women from 1981-2009 in Sweden and England to describe the importance of joint interpretation

Answer 18

• between these years, mortality rates increased in Sweden, and decreased in England
• using only mortality, you may assume Sweden has less superior lung cancer treatment/ facilities
• incidence rates showed correlation to mortality, increasing in Sweden and decreasing in England.
• as lung cancer patients tend to die within a year of diagnosis, we can see that there was an increasing burden of disease in Sweden, and a decreasing burden in England.
• the survival rate in Sweden is higher than England, disproving the original hypothesis

Question 19

What can’t we say the decline in mortality from 1990 in breast cancer was due to the introduction of screening?

Answer 19

• screening will not show a change in statistics straight after introduction
• the time between diagnosis, treatment, and death is long for breast cancer (compared to other cancers), decoupled mortality and incidence

Question 20

What the are + and - of incidence as a statistic?

Answer 20

+ insights into cancer etiology ( causes)
+ can employ cancer registry data, strict quality control
+ unaffected by changes in treatment/ survival
- influenced by screening & improvments in diagnosis
- affected by changing definitions

Question 21

What are the + and - of mortality as a statistic?

Answer 21

+ vital to inform public heath and heath-care priorities
+ information widely available from deaths registries
+ can be proxy for incidence in rapidly lethal cancers
+ can help evaluate effectiveness of treatment
- affected by trends in incidence & survival
- delayed reflection of progress in cancer survival
- subject to accuracy of death certification

Question 22

Explain why age must be standardized when looking at data, using stomach cancer in colombia and England as an example

Answer 22

• when looking at all ages, Colombia looks to have a lower incidence (19.9) than England (33.9)
• 84% of clombia’s population is below 44 years old whereas England has an overall older population
• stomach cancer has a higher incidence in older population
• when using age-standardized data, Colombia has a higher incidence compared to England