STATISTICS ON INCIDENCE, SURVIVAL RATES AND MORTALITY ASSOCIATED
WITH BRAIN TUMOURS IN AUSTRALIA
Prepared for the inaugural meeting of the
National Brain Tumour Advocacy Group
North Shore Private Hospital,
St Leonards, Sydney,
12-13 July 2003
By Denise Chang, KessiaCare Foundation Ltd, http://www.kessiacare.org.au/
Notes: In the following report "brain tumours" refers to
"cancers of the brain and other central nervous system". When examining data on
brain tumours be aware of differences in reporting. Only malignant cancers are included in
Australian Health and Welfare (AIHW) data because doctors are required by law to report
malignant cancers to State and Territory cancer registries but not benign cases.
The Australian Bureau of Statistics (ABS) data reports on underlying cause of death
from primary brain and other central nervous system tumours, including both
malignant and non-malignant (benign) tumours.
Appreciation is extended to Mr John Harding, Head of the Health Registers and Cancer
Monitoring Unit at the Australian Institute of Health and Welfare, Canberra, A.C.T., for
the provision and explanation of relevant statistics but all responsibility for
interpretation rests with the author.
This report is also available at http://www.ozbraintumour.org/btstats.htm (HTML format)
TABLE OF CONTENTS
1.
EXECUTIVE SUMMARY
2. RELEVANCE/POLICY IMPLICATIONS
3. BRAIN TUMOURS
4. THE NATIONAL CANCER STATISTICS CLEARING HOUSE
5. STATISTICAL TERMS
6. GENERAL CANCER STATISTICS
7. BRAIN TUMOUR INCIDENCE
8. BRAIN TUMOUR SURVIVAL STATISTICS AND YEARS OF LIFE LOST
9. BRAIN TUMOUR MORTALITY
10. TRENDS IN BRAIN TUMOUR INCIDENCE AND MORTALITY
11. INTERNATIONAL COMPARISON
12. HOSPITAL INPATIENT STATISTICS
Appendix 1: A Primer of Brain Tumors, 7th Edition, American Brain Tumor
Association
TABLE OF FIGURES
Table 1. New
cases of cancers of the brain and central nervous system, sex, Australia, 1999
Figure 1. Distribution of cancers of the brain and central nervous system, Australia,
1999
Table 2. New cases of cancers of the brain and central nervous system, age and sex,
Australia, 1999
Table 3. New cases of cancers of the brain and central nervous system, distribution by
age, Australia, 1999
Table 4. New cases of cancers of the brain and central nervous system,
distribution by cancer within age group, Australia, 1999
Table 5. Cancers of the brain and other central nervous system, number of new cases and
age standardised rates, 1999
Figure 2. Number of new cases of cancer of the brain and other CNS, by 5 year age
groups, 1999
Figure 3. Number of new cases of cancer of the brain and other CNS, by 5 year age
groups and gender, 1999
Table 6. Five-year relative survival ratios for all registrable cancers
and selected individual cancer sites, diagnosis period, males, Australia
Table 7. Five-year relative survival ratios for all registrable cancers
and selected individual cancer sites, diagnosis period, females, Australia
Table 8. Comparison of deaths caused by cancer of the brain/CNS and
leukaemia, by age at death, 2001, Australia
Table 9. Cancers of the brain and central nervous system: incidence and
mortality, Australia, 1982-1999
Table 10. Cancers of the brain and nervous system, incidence and
mortality, males and females, GLOBOCAN 2000 database
1. EXECUTIVE SUMMARY
According to the ABS Causes of Death data a total 1,205 people died from cancers of the
brain and other central nervous system tumours (cancerous and non-cancerous [benign]) in
2001. This included 61 deaths where a benign (non-cancerous tumour) was the underlying
cause of death. This compares with 1,385 people who died from leukaemia.
Brain tumours are the most common solid tumours in childhood (about a fifth of
all children's cancers). Together, lymphatic leukaemia and cancers of the brain and the
central nervous system accounted for nearly 44% of all cancers diagnosed in children aged
0-14 years in 1998.
Brain tumours accounted for the most cancer related deaths in children aged 0-14 years,
with 38% of cancer deaths in 2000 attributed to cancers of the brain and other central
nervous system (compared to 34% for leukaemia). This pattern was repeated in 2001, with 45
deaths due to brain tumours compared to 37 for leukaemia in children aged 0-14 years.
On average, if deaths from other causes are excluded, only one in four persons diagnosed
with a brain tumour will be alive five years following their diagnosis.
In 1999 there were a total of 1,361 new cases of cancer of the brain and other central
nervous system reported. Males accounted for more than half of all brain tumours diagnosed
(58% male, 42% female). (This excludes non-cancerous [benign] brain and other central
nervous system tumours.)
In 1996, there was an estimated 16,713 years of life lost in Australia due to
"brain cancer" — 9,636 for males and 7,076 for females. This was estimated
for all persons with brain cancer who died in 1996 by summing the difference between age
at death and life expectancy for the population at that age. In 1996, there was also an
estimated 1,060 years of life lost due to disability from brain cancer—663 for males
and 397 for females. Source: AIHW: Mathers C, Voc T, Stevenson C. The burden of
disease and injury in Australia. AIHW cat. no. PHE 17. Canberra:AIHW. 1999.
The median age for diagnosis for brain tumours was 55-59 years for males and 60-64 years
for females.
The median age at diagnosis for brain tumours for all persons was 55-59 years, lower
than for cancers as a whole (median age at diagnosis for all cancers 65-69 years).
According to AIHW data 7 people per 100,000 population were diagnosed with brain tumours
in Australia in 1999. When converted to world age-standardised rates, 7.4 per 100,000
males and 4.8 per 100,000 females were newly diagnosed with brain tumours in Australia.
The most common cancers of the brain and central nervous system were cancer of the
frontal lobe (271 cases), cancer of the temporal lobe (257 cases) and cancer of the
parietal lobe (177 cases). However, there were also 254 cases of cancer of the brain where
site within the brain was not specified. National statistics on type of
brain tumour are not publicly available at the present time.
Most cases of cancers of the cerebellum, cerebral ventricle, and brain stem occur in
young people.
Cancers of the cerebrum and lobes are most likely to occur in people aged 55 years or
more.
A number of cancers including breast cancer, bowel cancer and brain cancer are diseases
which occur at much higher rates in affluent countries. Australia’s rates of brain
cancer incidence and mortality are therefore high by world standards, but are on a par
with countries such as New Zealand, Canada, the USA, and the United Kingdom. Norway,
Sweden and Greece have much higher rates than Australia, possibly because of the inclusion
of benign tumour data.
2. RELEVANCE/POLICY IMPLICATIONS
There are almost 1,400 new cases a year of
malignant brain tumours in Australia and hundreds more of benign brain tumours that can be
just as deadly. More than 1,200 people die each year from malignant and benign brain
tumours.
The number of new cases of malignant brain tumours in
Australia has increased by 21% during the last 10 years from 1122 in 1989 to 1361 in 1999.
(See 10.1, 10.2)
The numbers of new cases and of deaths per 100,000
population due to brain tumours in Australia are high by world standards (see 11.1), and
survival after 5 years is poor - only 1 in 4 cases.
Brain tumours are also important because there are
115 new cases per year among children. It is not only a disease that occurs among older
people. In the 0-14 age group brain tumours kill more children than leukaemia (see 1.3,
9.2, 9.3)
This provides strong evidence for a need for more
research into why brain tumour incidence and mortality are high and whether improvements
can be made in diagnosis and treatment that will reduce mortality and increase survival
times.
|
3. BRAIN TUMOURS
A brain tumour is a mass of unnecessary and abnormal cells growing in the brain. A
tumour that starts in the brain is a primary brain tumour, which in turn may be
grouped into "benign" and "malignant" tumours.
A benign tumour consists of very slow growing cells, usually has distinct
borders, and rarely spreads. Treatment and/or surgery is often effective, however, if a
benign tumour is located in a vital area of the brain, it can be considered life
threatening (rather than "malignant"). So, unlike most benign tumours,
noninvasive tumours of the brain/CNS have the potential to be fatal.
A malignant brain tumour is life threatening, invasive and usually rapid growing.
This is in contrast to other malignant tumours of the body which are invasive but grow
more slowly.
Brain "tumour" vs brain "cancer". Primary brain tumours rarely
spread outside the brain and spinal cord. In order to be labelled a cancer, a tumour must
have the ability to metastasize and spread to other organs of the body. Primary brain
tumours rarely spread in this way but the statistical terms used in this area have
traditionally involved use of the term 'brain cancer'.
However, cancer cells which begin growing elsewhere in the body and then travel to the
brain form metastatic brain tumours. All metastatic brain tumours are malignant since they
begin as cancer elsewhere in the body.
There are more than 160 different types of brain tumours, of which some 40 are
classified as malignant. It is possible that each type of tumour has different causal
factors, and it's degree of severity or malignancy (the grade of tumour), it's
location within the brain, the size of surrounding tissue mass affected by the tumour,
whether it is diffuse or defined, are just some of the factors to be considered when
classifying , treating or researching brain tumours.
Brain tumours are classified in several ways. The first level of classification is
according to the World Health Organisation's International Classification of Diseases, now
up to it's 10th edition (ICD-10). Finer detail of brain tumour types is found
in WHO's cancer classification system and modifications of it.
The American Brain Tumor Association's "A Primer of Brain Tumors" is intended
to be a reference manual for brain tumour patients and their carers. Appendix 1 contains
the full chapter text on which most of the above information is based. The Primer is
available on-line at http://www.abta.org/buildingknowledge5.htm
4. THE NATIONAL CANCER STATISTICS CLEARING HOUSE
- The NCSCH was established in 1986 to foster the development and dissemination of
national cancer statistics for Australia. It is supervised by the Australasian Association
of Cancer Registries (AACR) and is operated by the Austalian Institute of Health and
Welfare in collaboration with the AACR.
- The NCSCH aims to specifically:
. enable computation and publication of national statistics on cance
. allow tracking of interstate movement of cancer cases via record linkage
. facilitate exchange of scientific and technical information between cancer registries
and promote standardisation in the collection and classification of cancer data; and
. facilitate cancer research both nationally and internationally.
3. The NCSCH receives data from individual State and Territory cancer registries on
cancer diagnosed in residents of Australia. This commenced with cases first diagnosed in
1982. Data from this collection is used to compile national cancer incidence and
prevalence statistics.
4. With regard to mortality data, cancer deaths are recorded as an underlying cause of
death or associated cause of death on a person's death certificate. This is forwarded to
the Registrar of Births, Deaths and Marriages in each state or territory, who makes this
information available to the Australian Bureau of Statistics for coding purposes. ABS is
now trying to improve the accuracy of cause of death cancer coding by referring these
cases to state and territory cancer registries. The cancer registries then advise ABS of
the exact cancer description and ICD code. However, this is not yet done in all States.
5. This procedure has implications for the gathering of accurate data relating to brain
tumour deaths.
6. The latest available cancer statistics are documented in AIHW's publication
"Cancer in Australia 1999".
5. STATISTICAL TERMS
Incidence means how many people get a particular type of disease every year, usually
expressed as the number of new cases per 100,000 people in the general population. Because
some conditions are more age-specific, incidence by age is also an important measure.
Survival after a diagnosis of cancer is an important measure in assessing the broad
impacts of prevention, of early detection methods, and of treatment. Relative survival is
the ratio between what actually happened to a group of people with cancer and what would
normally have occurred to them in the absence of cancer. A common measure is the 5-year
relative survival ratio, which is the relative survival over the first 5 years following a
diagnosis of cancer. A relative survival rate of 100% indicates that the disease has made
no difference to the survival of the group over this period. A survival rate of less than
100% indicates that fewer members of the group survived for 5 years than would have been
expected for similar people in the general population.
Mortality statistics mean the number of people who have died from a particular condition
in a year.
6. GENERAL CANCER STATISTICS
- Cancer is an important cause of morbidity and mortality in Australia. Excluding
non-melanocytic skin cancers, there were 82,185 new cancer cases and 34,695 deaths due to
cancer in Australia in 1999. Almost one in three males (29%) and one in four females (25%)
die from cancer ["Cancer in Australia 1999", AIHW].
- The most common types of cancer are: Cancers of the breast (13.0%), colon (14.2%),
prostate (12.5%), skin (10.0%) and lung (9.5%) which together accounted for over half of
all new cancer cases registered in 1999.
- In 2000, cancer was the second leading cause of death in children aged 0-14 years ["Australia's
Children: Their health and well-being 2002", AIHW]
7. BRAIN TUMOUR INCIDENCE
- There were 1,361 new cases of cancers of the brain and central nervous system in 1999,
of which 792 (58.2%) were males. In total, this accounted for 1.6% of all new cancer cases
[National Cancer Statistics Clearing House, AIHW data cube].
- The most common cancers of the brain and central nervous system were cancer of the
frontal lobe (271 cases), cancer of the temporal lobe (257 cases) and cancer of the
parietal lobe (177 cases). However, there were also 254 cases of cancer of the brain where
site within the brain was not specified.
- Cancers of the cerebrum and lobes are most likely to occur in people aged 55 years or
more.
- Most cases of cancers of the cerebellum, cerebral ventricle, and brain stem occur in
young people.
- Incidence of brain cancer between 1990 and 1999 increased in males by an average of 0.2%
per annum and decreased in females by an average of 1.0% per annum.
- In children, leukaemia (a cancer of white blood cells) is the most common cancer,
accounting for approximately one-thrid of all childhood cancers. ['Australia's
Children: Their health and well being 2002", AIHW]
- Brain tumours are the most common solid tumours in childhood and make up about a
fifth of all children's cancers (Miller et al. 1995, from 'Australia's Children: Their
health and wellbeing 2002", AIHW]
- For example, in 1998 the most common types of cancers among children aged 0-14 years
were lymphatic leukaemia (4.1 per 100,000 boys, 3.8 per 100,000 girls) and cancers of the
brain and the central nervous system (3.4 per 100,000 boys, 3.7 per 100,000 girls). These
accounted for nearly 44% of all cancers diagnosed in this age group [AIHW and AACR
2000].
Table 1. New cases of cancers of the brain and central nervous
system, sex, Australia, 1999
Source: National Cancer
Statistics Clearing House, Australian Institute of Health and Welfare.
Figure 1. Distribution of
cancers of the brain and central nervous system, Australia, 1999
Source: National Cancer Statistics Clearing House, Australian Institute of Health and
Welfare.
Table 2. New cases of cancers of the brain and central nervous
system, age and sex, Australia, 1999
Source: National Cancer Statistics
Clearing House, Australian Institute of Health and Welfare
Table 3. New cases of
cancers of the brain and central nervous system, distribution by age, Australia, 1999
Source: National Cancer Statistics Clearing House, Australian
Institute of Health and Welfare
Table 4. New cases of cancers of the brain and central nervous
system, distribution by cancer within age group, Australia, 1999
Source: National Cancer Statistics Clearing House, Australian
Institute of Health and Welfare
Table 5. Cancers of the brain and other central
nervous system,
number of new cases and age standardised rates, 1999
| |
Males |
Females |
Persons |
| New cases |
784 |
564 |
1,348 |
| % of all registrable cancers |
0.95 |
0.69 |
1.64 |
| Rates per 100,000
population |
|
|
|
| Crude rate |
8.3 |
5.9 |
7.1 |
| Australian age-standardised
rate (1991) |
8.1 |
5.4 |
6.7 |
| World age-standardised rate |
7.4 |
4.8 |
6.0 |
Source: National Cancer Statistics Clearing House; AIHW interactive
cancer data cube
7 people per 100,000 population were diagnosed with cancer of the brain or other CNS in
Australia in 1999.
When converted to world age-standardised rates, 7.4 per 100,000 males and 4.8 per
100,000 females were newly diagnosed with brain/CNS cancer in Australia.
- For an international comparison, Australian figures are almost identical to Ireland's
world age-standardised rates, where 7.0 per 100,000 males and 4.8 per 100,000 females were
diagnosed with malignant cancer of the brain in 1994-1996 [All-Ireland Cancer
Statistics 1994-1996].
Figure 2. Number of new cases of cancer of the
brain and other CNS,
by 5 year age groups, 1999
Source: National Cancer Statistics Clearing House; AIHW interactive
cancer data cube
- Median age at diagnosis for cancer of the brain and other CNS was 55-59 years, lower
than for cancers as a whole (median age at diagnosis for all cancers 65-69 years).
Figure 3. Number of new cases of cancer of the
brain and other CNS,
by 5 year age groups and gender, 1999
Males 
Females
Source: National Cancer Statistics Clearing House; AIHW interactive
cancer data cube
- In 1999, a total of 1,361 new cases of cancer of the brain and other CNS were reported.
Males accounted for more than half of all brain tumours diagnosed (58% male, 42% female).
- The median age for diagnosis was 55-59 years for males and 60-64 years for females.
- In summary, there is evidence to suggest that more males are diagnosed with cancer of
the brain and other CNS than females, and at a slightly lower age.
8. BRAIN TUMOUR SURVIVAL STATISTICS AND YEARS OF LIFE LOST
- The average 5-year relative survival proportion for all registrable cancers diagnosed in
Australia between 1992 and 1997 was 56.8% for males and 63.4% for females.
- One in four males diagnosed with cancers of the brain were alive five years following
their diagnosis (23.8%) compared to 41.2% of males diagnosed with leukaemia.
- Figures are similar for the 5-year relative survival proportion for females diagnosed
with cancers of the brain at 23.8%, compared to 43.2% of females diagnosed with leukaemia.
- In terms of prognosis, cancers of the brain rate amongst the five lowest relative
survival rates for males and fourth lowest for females.
In 1996, there were an estimated 16,713 years of life lost in Australia due to brain
cancer—9,636 for males and 7,076 for females. This was estimated for all persons with
brain cancer who died in 1996 by summing the difference between age at death and life
expectancy for the population at that age.
In 1996, there were also an estimated 1,060 years of life lost due to disability from
brain cancer—663 for males and 397 for females. [Source: AIHW: Mathers C, Voc
T, Stevenson C. The burden of disease and injury in Australia. AIHW cat. no. PHE 17.
Canberra:AIHW. 1999.]
Table 6. Five-year relative survival ratios for
all registrable cancers and
selected individual cancer sites, diagnosis period, males, Australia
| |
Diagnosis period |
| Cancer site |
1982-1986 |
1987-1991 |
1992-1997 |
| Males |
(Per cent) |
| Testis Melanoma
Thyroid
Prostate
Hodgkin's lymphoma
Bladder
Kidney
Colon
Rectum
Non-Hodgkin's lymphoma
Leukaemia
Brain
Stomach
Unknown primary
Lung
Pancreas
All registrable cancers |
91.1
83.0
81.0
59.3
74.1
71.2
50.8
50.2
48.7
49.6
39.4
24.8
19.2
11.7
9.3
4.2
43.8 |
95.2
87.2
82.6
64.3
79.1
71.6
53.7
54.7
51.2
51.1
43.3
24.3
21.6
13.0
10.7
4.4
48.1 |
95.4*
90.0*
87.9
82.7*
82.6*
70.8
59.9*
58.3*
56.6*
54.6*
41.2
23.8
22.6*
13.4
11.0*
5.4
56.8* |
* Change between 1982-1986 and 1992-1997 is statistically significant at the 95% level.
Source: AIHW and AACR 2001
Table 7. Five-year relative survival ratios for
all registrable cancers and
selected individual cancer sites, diagnosis period, females, Australia
| |
Diagnosis period |
| Cancer site |
1982-1986 |
1987-1991 |
1992-1997 |
| Females |
(Per cent) |
| Thyroid Melanoma
Hodgkin's lymphoma
Breast
Uterus
Cervix
Bladder
Rectum
Colon
Kidney
Non-Hodgkin's lymphoma
Leukaemia
Ovary
Stomach
Brain
Lung
Unknown primary
Pancreas
All registrable cancers |
87.8
90.9
73.8
72.3
76.1
69.6
67.2
52.3
51.3
49.4
49.9
39.4
34.4
21.1
24.1
11.8
10.4
4.1
55.3 |
91.9
93.5
79.9
77.8
78.5
72.0
65.2
56.0
54.7
52.7
54.6
44.2
37.7
21.8
25.3
11.9
10.9
5.4
59.1 |
95.6*
94.6*
84.4*
84.0*
81.4*
74.6*
64.7
60.6*
58.7*
57.5*
55.8*
43.2*
42.0
24.8*
23.8
14.0*
11.5
5.2
63.4* |
* Change between 1982-1986 and 1992-1997 is statistically significant at the 95% level.
Source: AIHW and AACR 2001
5-year relative survival for all registrable cancers increased between 1982-1986 and
1992-1997 on average from 43.8% to 56.8% for males and from 55.3% to 63.4% for females.
However, cancers of the brain showed small decreases in relative survival over this
period for both males and females. Although these decreases were not statistically
significant, the figures indicate that the relative survival for brain tumours remains
unchanged whilst survival rates for most other cancers have improved on average.
9. BRAIN TUMOUR MORTALITY
Although brain tumours account for a relatively small proportion of new cancer cases
reported each year, brain tumours have a disproportionately higher mortality rate and
decreased survival rates when compared to the more common types of cancer.
In 2000, 105 children aged 0-14 years died from cancer. Most of the deaths (38% or 40
deaths) were due to cancer of the eye, brain and other parts of the CNS; 36 deaths (34%)
were due to cancers of the lymphoid and haematopoietic tissues.
Again in 2001, cancer of the brain and other CNS accounted for the most childhood cancer
deaths, with 45 deaths, compared to 37 children who died from leukaemia.
In total 1,205 people died from cancers of the brain and other CNS in 2001, compared to
1,385 who died from leukaemia.
Table 8. Comparison of deaths caused by cancer of
the brain/CNS and leukaemia,
by age at death, 2001, Australia
| |
Cancer of the brain and
other CNS(1) |
Leukaemia(2) |
| |
|
|
| 0-4 5-9
10-14
15-19
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59 |
17
14
14
11
9
12
24
38
51
61
114
126 |
12
17
8
11
12
16
19
19
27
30
58
72 |
| 60-64 65-69
70-74
75-79
80-84
85+
TOTAL |
109
138
151
156
88
72
1,205 |
97
126
199
251
212
199
1,385 |
- Includes ICD-10 codes C70-C72, D32, D33, D42, D43
- Includes ICD-10 codes C91-C95
Source: Private correspondence with Australian Bureau of Statistics, Deaths Collection,
1997+
10. TRENDS IN BRAIN TUMOUR INCIDENCE AND MORTALITY
- The number of new cases of cancers of the brain and central nervous system has increased
from 891 in 1982 to 1,361 in 1999. The age-standardised rate increased from 6.5 per
100,000 population to 7.3 per 100,000 population during the same period.
- The number of deaths from cancers of the brain and central nervous system increased from
680 in 1982 to 1,030 in 1999. Statistically the age-standardised mortality rate was fairly
stable during this period. In 1999 the age-standardised death rate from cancers of the
brain and central nervous system was 5.6 per 100,000 population.
Note: Rates are expressed per 100,000 population and
age-standardised (AS Rate) to both the Australian 2001 Standard Population and the current
World Standard Population.
Source: National Cancer Statistics Clearing House, Australian
Institute of Health and Welfare.
11. INTERNATIONAL COMPARISON
- A number of cancers including breast cancer, bowel cancer and brain cancer are diseases
which occur at much higher rates in affluent countries. Australia’s rates of brain
cancer incidence and mortality are therefore high by world standards, but are on a par
with countries such as New Zealand, Canada, the USA, and the United Kingdom. Norway,
Sweden and Greece have much higher rates than Australia.
Table 10. Cancers of the
brain and nervous system, incidence and mortality, males and females, GLOBOCAN 2000
database
12. HOSPITAL INPATIENT STATISTICS
(Source: AIHW Australian hospital statistics database)
- In 2000–01, there were 4,739 separations from hospitals in Australia of persons
with a principal diagnosis of cancer of the brain or central nervous system, with an
average stay of 11.2 days. There were 659 deaths.
- Treatment was mainly acute care (4,020 separations) and palliative care (607
separations).
- The most common procedures undertaken were:
– CAT scan 1,296
– MRI 1,119
– removal of intercranial tumour 1,113
– examination of skull, meninges or brain 827
– biopsy of brain or meninges 428
– chemotherapy 373
– injection or transfusion of terapeutic or prophylactic substance
– transfusion of blood and gamma globulin
- The most common additional diagnoses were:
– hemiplegia 639
– personal history of certain other diseases 396
– hypertension 359
– convulsions, not elsewhere classified 347
– secondary malignant cancer of other sites 309
– speech disturbances, not elsewhere classified 302
– problems related to lifestyle 280
– Type 2 diabetes 260
– epilepsy 218
Appendix 1: A Primer of Brain Tumors, 7th
Edition,
American Brain Tumor Association
Brain Tumour Basics
The adult body normally forms new cells only when they are needed to replace old or
damaged ones. Infants and children form new cells to complete their development in
addition to those needed for repair. A tumor develops if normal or abnormal cells multiply
when they are not needed.
A brain tumor is a mass of unnecessary, and abnormal, cells growing in
the brain.
When doctors describe brain tumors, they often use the words "benign" or
"malignant." Those descriptions refer to the degree of malignancy or
aggressiveness of a brain tumor. It is not always easy to classify a brain tumor as
"benign" or "malignant" as many factors other than the pathological
features contribute to the outcome.
This chapter was updated by Peter C. Burger, MD, Johns Hopkins Hospital, Department of
Pathology, Baltimore, Maryland. We thank him for his assistance with that update.
PRIMARY BRAIN TUMORS
A tumor that starts in the brain is a primary brain tumor. Glioblastoma, astrocytoma,
medulloblastoma, and ependymoma are examples of primary brain tumors. Primary brain tumors
can be grouped into "benign" tumors and "malignant" tumors.
Benign brain tumors
A "benign" brain tumor consists of very slow growing cells, usually has
distinct borders, and rarely spreads. When viewed microscopically, the cells have an
almost normal appearance. Surgery alone might be an effective treatment for this type of
tumor. A brain tumor composed of benign cells, but located in a vital area, can be
considered to be life-threatening - although the tumor and its cells would not be
classified as "malignant."
Malignant brain tumors
A malignant brain tumor is life-threatening, invasive, and usually rapidly growing.
Other malignant tumors are invasive but grow more slowly. Malignant brain tumors are often
called brain cancer. Since primary brain tumors rarely spread outside the brain and spinal
cord, they do not exactly fit the general definition of "cancer" -- a tumor that
has the ability to spread to other organs of the body. Since brain tumors generally do not
spread to other organs, they do not meet the true definition of cancer. Thus, we say that
brain tumors are either "benign" or "malignant."
Brain tumors can be malignant if they are located in a critical part of the brain or
cause life-threatening damage.
Some types of malignant brain tumors can spread to other locations in the brain and
spine, but they rarely spread to other parts of the body. They invade and destroy healthy
tissue. They lack distinct borders due to their tendency to send "roots" into
nearby normal tissue. They can also shed cells that travel to distant parts of the brain
and spine by way of the cerebrospinal fluid. Some malignant tumors, however, do remain
localized to a region of the brain or spinal cord.
METASTATIC BRAIN TUMORS
Cancer cells that begin growing elsewhere in the body and then travel to the brain form
metastatic brain tumors. For example, cancers of the lung, breast, colon and skin
(melanoma) frequently spread to the brain. All metastatic brain tumors are, by definition,
malignant.
All metastatic brain tumors are malignant since they begin as cancer elsewhere in the
body.
TUMOR NAMES
Tumors are diagnosed and then named based on a classification system. Most centers now
use the World Health Organization classification system for this purpose.
TUMOR GRADING
Tumors are graded to facilitate communication, to plan treatment, and to predict
outcome. The grade of a tumor indicates its degree of malignancy. Grade is assigned based
on the tumor's microscopic appearance using some or all of the following criteria:
- similarity to normal cells (atypia)
- rate of growth (mitotic index)
- indications of uncontrolled growth-dead tumor cells in the center of the tumor
(necrosis)
- potential for invasion and/or spread (infiltration) based on whether or not it has a
definitive margin (diffuse or focal)
- blood supply (vascularity)
Using the WHO (World Health Organization) grading system, grade I tumors are the least
malignant and are usually associated with long-term survival. The tumors grow slowly, and
have an almost normal appearance when viewed through a microscope. Surgery alone might be
an effective treatment for this grade of tumor. Pilocytic astrocytoma, craniopharyngioma,
and many tumors of neurons - for example, gangliocytoma and ganglioglioma - are examples
of grade I tumors.
Grade II tumors are relatively slow growing but have a slightly abnormal microscopic
appearance. Some can invade adjacent normal tissue and recur. Sometimes these tumors recur
as a higher grade.
Grade III tumors are, by definition, malignant, although there is not always a sharp
distinction between a grade II and a grade III tumor. The cells of a grade III tumor are
actively reproducing abnormal cells and infiltrate adjacent normal brain tissue. These
tumors tend to recur, often as a higher grade.
The most malignant tumors are given a grade of IV. They reproduce rapidly, can have a
bizarre appearance when viewed under the microscope, and infiltrate widely. These tumors
induce the formation of new blood vessels so they can maintain their rapid growth. They
also have areas of dead cells in their center. Glioblastoma multiforme is the most common
example of a grade IV tumor.
Tumors often contain several grades of cells. The highest or most malignant grade of
cell determines the grade, even if most of the tumor is a lower grade.
Some tumors undergo change. A "benign" growth might become malignant. In some
tumors, a lower-grade tumor might recur as a higher-grade tumor. Only rarely, after
treatment, do higher-grade tumors become lower-grade.
All grading systems have inherent difficulties - they are not precise.
- criteria used to assign grades are subject to interpretation by each pathologist
- tumors are not uniform, and the sample examined might not be representative of the
entire tumor.
CHANGE OF DIAGNOSIS
Your diagnosis and the name of your tumor might be changed. There are several factors
that might cause the change in diagnosis:
- Inspecting only a small sample of the tumor, such as that obtained by a needle biopsy,
might not be representative of the whole tumor.
- Tumors do not always remain static. They can undergo transformation, usually to a higher
grade. If that occurs, the name and grade of the tumor might change. A grade III
anaplastic/malignant astrocytoma could become a glioblastoma (also called a grade IV
astrocytoma).
- You should also be aware that classification of brain tumors by the pathologist is a
subjective procedure that is not always straightforward. Different pathologists might
disagree about the classification, and grade, of the same tumor.
TUMOR STAGING (PRIMARY BRAIN TUMORS)
"Staging" determines if a tumor has spread beyond the site of its origin. In
cancers such as breast, colon, or prostate this is primarily accomplished by a
pathologist's examination of nearby tissue such as lymph nodes. In those cancers, staging
is a basic part of the diagnostic work-up.
Staging for central nervous system (CNS) tumors is usually inferred from CT scan or MRI
images, or by examining the cerebrospinal fluid. Scans taken after surgery are used to
determine if there is remaining tumor. CNS tumors that are especially prone to spread are
studied with both scan images and laboratory tests. For example, patients with
medulloblastoma will often have their cerebrospinal fluid examined for the presence of
tumor cells. Those patients will also have scans of their spinal cord because of that
tumor's tendency to spread there.
Staging information often influences treatment recommendations and prognosis.
PROGNOSIS
Prognosis means prediction. It is an educated guess about the future course of a
disease in a specific individual. Prognosis is based on the type of tumor, its grade,
location, and spread (if any), the age of the patient, how long the patient had symptoms
before the tumor was diagnosed, how much the tumor has affected the patient's ability to
function, and the extent of surgery if surgery was performed.
The type of therapy is also instrumental. Certain tumors, although malignant, can be
cured by radiation therapy or chemotherapy. Others, by virtue of their location, may
ultimately be lethal in spite of their "benign" appearance under the microscope.
ABOUT "LESIONS"
"Lesion" is a general term which refers to any change in tissue. Tumor,
inflammation, blood, infection, scar tissue, or necrosis (dead cells) are all examples of
lesions that may be found in the brain. Determining the nature of the lesion is the work
of the pathologist.
Table 9. Cancers of the brain and central
nervous system: incidence and mortality, Australia, 1982-1999