Modeling the burden of cancer in Canada
The Population Health Model (POHEM) is a policy analysis tool that
helps answer “what-if” questions about the health and
economic burden of specific diseases and the cost-effectiveness
of administering new diagnostic and therapeutic interventions. This
simulation model is particularly pertinent in an era of fiscal restraint,
when new therapies are generally expensive and difficult policy
decisions are being made. More important, it provides a base for
a broader framework to inform policy decisions using comprehensive
disease data and risk factors.
We acknowledge our valued collaborator, Dr. William K. Evans, medical
oncologist and Executive Vice President of Cancer Care Ontario,
who contributed untold hours to the development of the cancer models
described below.
“Base case” models
of cancer care
Chemotherapy for advanced lung
cancer
Post-surgical breast cancer hospitalization
Administering tamoxifen to women
at high risk of breast cancer
Population-based colorectal cancer
(CRC) screening in Canada
Future directions: Canadian Burden
of Disease, Injury and Risk Factors (CBD)
In summary
Microsimulation Modeling
Related reading
See our articles
“Base case” models of cancer care
Our “base case” models were the first to comprehensively
estimate the lifetime costs of treating breast, lung and colorectal
cancer in Canada. This work depended on close collaboration with
medical experts and access to many data sources for risk factors,
disease incidence, stage at diagnosis, typical diagnostic and therapeutic
approaches, disease progression, follow-up practice patterns, treatment
at relapse and terminal care, and all associated costs.
All three cancer models highlighted that hospitalization for diagnostic
work-up, initial surgery, palliation and terminal care was the main
cost driver (see Figure 1). We have also modeled coronary heart
disease, osteoporosis, arthritis and osteoporotic fractures.
Chemotherapy for advanced lung cancer
Best supportive care had generally been the standard therapy for
advanced non-small cell lung cancer in Canada. As cancer management
patterns changed over time, we modified our microsimulation models
to evaluate the impact of new interventions.
Using a decision framework comparing current outpatient chemotherapy
regimens by cost per life-year saved and by quality-adjusted life
year gained, we found that the clinical standard of vinorelbine
plus cisplatin was the most cost-effective of the new regimens.
The Policy Advisory Committee of Cancer Care Ontario considered
these results when deciding to fund vinorelbine and gemcitabine
in Ontario.
Post-surgical breast cancer hospitalization
In 1995, the average length of hospital stay for women undergoing
breast conserving surgery and mastectomy was about five and six
days, respectively. We modeled the impact of outpatient breast conserving
surgery and a two-day hospital stay for mastectomy and found that
home care costs of $453 per patient could potentially result in
savings of about $20 million for breast conserving surgery alone
and $13 million for mastectomy. (This assumed a 90% eligibility
for home-based post-operative care and a 5% re-admission rate.)
Reducing post-surgical breast cancer hospitalization and providing
optimal home care support could produce major health care savings.
Administering tamoxifen to women at high risk
of breast cancer
The Breast Cancer Prevention Trial (see Fisher, 1998) demonstrated
that tamoxifen could reduce the risk of invasive breast cancer in
high-risk women by 49%. With the cut-off used in this trial, a five-year
risk of 1.66% or more for developing breast cancer, 23% of Canadian
women in the year 2000 would be eligible for this intervention.
From another perspective, the lifetime probability for a woman being
eligible for tamoxifen was 85%.
Our simulation of this trial suggested that the detrimental effects
of tamoxifen, which include endometrial cancer, coronary heart disease,
stroke and deep vein thrombosis, likely outweigh the protective
effect of tamoxifen on breast cancer for the majority of eligible
women. Although it supported the use of tamoxifen for the 4% of
Canadian women with a five-year predicted risk of 3.32% or more,
our overall results raised questions about the use of tamoxifen
for some otherwise healthy Canadian women.
Population-based colorectal cancer (CRC) screening
in Canada
We also used our colorectal cancer simulation model to estimate
the potential impact of population-based screening in Canada. Randomized
controlled trials have shown the efficacy of screening for colorectal
cancer using the faecal occult blood test with follow-up by colonoscopy.
Applied to a Canadian context, we found that biennial screening
of 67% of individuals aged 50-74 in 2000 would result in an estimated
10-year CRC mortality reduction of 16.7%. The life expectancy of
the cohort would increase by 15 days and the total demand for colonoscopy
would increase by at least 15%. The estimated cost of screening
would be $112 million per year with a cost-effectiveness ratio of
about $12,000 per life-year gained (discounted at 5%).
This work helped the National Committee on CRC Screening to assess
the potential impact and feasibility of population-based screening
in Canada. Their report will be released soon.
Future directions: Canadian Burden of Disease,
Injury and Risk Factors (CBD)
The microsimulation framework described above is a valuable tool
to guide clinicians and health policy makers, integrating detailed
documentation of current treatment modalities and costs of treatment
for a specific disease. An expanded simulation framework will be
developed to evaluate broader policies and programs for priority
setting, allowing concurrent examination of a comprehensive set
of diseases and the major risk factors associated with them.
In collaboration with Health Canada, the University of Manitoba,
the University of Ottawa and the Montreal Centre Regional Health
and Social Services Board, we are now developing such an expanded
framework. This three-year project will estimate the Canadian burden
of disease across disease groupings and risk factors. It will also
provide a simulation infrastructure for evaluation of broad intervention
strategies by policy analysts and projection of the future burden
of disease and injury in Canada. This project has been peer-reviewed,
and unanimously endorsed by members of the Advisory Committee on
Population Health (ACPH) of the Conference of Deputy Ministers of
Health.
In summary
An integrative microsimulation framework that can evaluate treatment
modalities and overall costs of treating specific diseases such
as lung or breast cancer is a valuable tool for clinicians and health
policy makers. It answers “what-if” questions about
the relative impact of alternative scenarios related to new therapies
and intervention strategies.
Further work will broaden this approach to estimate the burden
of disease, injury and risk factors in the Canada population, considering
other health conditions that occur with or as a result of these
diseases. The analytic results will help assess the impact of population
health interventions within and across disease groupings and by
risk factor. Answers to questions such as “What is the impact
of hypertension or diabetes on cardiovascular diseases?” or
“How is the burden of disease distributed by socio-economic
status?” can inform program prioritization and resource allocation.
Microsimulation Modeling
The POHEM microsimulation framework integrates diverse
health data, analytical results and resource utilisation
data for further analyses and decision making. The model
generates a sample of synthetic individuals and ages them
over time, based on data about risk factors, disease onset
and progression, and consequent effects on health and functional
status. The resulting longitudinal data set represents the
full life cycle of a cohort of individuals born in the same
year.
Using the Monte Carlo method, individuals are assigned
demographic and labour force characteristics, health risk
factors, and individual health histories typical of Canadians.
Disease progression and case fatality are modeled allowing
transition times in various health states such as stages
of cancer progression. In these disease models, co-morbidities
and competing risks from multiple disease processes are
explicitly modeled.
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Related reading
Harvard School of Public Health on behalf of the World Health
Organization and the World Bank. The global burden of disease: a
comprehensive assessment of mortality and disability from diseases,
injuries, and risk factors in 1990 and projected to 2020. Murray
CJL, Lopez AD, eds. Cambridge (MA): Harvard University Press, 1996.
http://www.hsph.harvard.edu/organizations/bdu/GBDseries.html
Mathers C, Vos T, Stevenson C. The burden of disease and injury
in Australia. Cat. no. PHE 17. Canberra: Australian Institute of
Health and Welfare, 1999.
http://www.aihw.gov.au/publications/index.cfm/title/5180
Victorian Burden of Disease Study: Mortality
http://hna.ffh.vic.gov.au/phd/9903009/
Victorian Burden of Disease Study: Morbidity
http://www.dhs.vic.gov.au/phd/9909065/index.htm
See our articles
Berthelot J-M, Will BP, Evans WK, Coyle D, Earle CC, Bordeleau L.
Decision framework for chemotherapeutic interventions for metastatic
non-small cell lung cancer. J Natl Cancer Inst 2000; 92(16): 1321-9.
Evans WK, Will BP, Berthelot J-M, Logan DM, Mirsky DJ, Kelly N.
Breast cancer: better care for less cost: is it possible? Int J
Technol Assess 2000; 16(4): 1168-78.
Flanagan WM, Le Petit C, Berthelot J-M, White KJ, Coombs BA, Jones-McLean
E. Potential impact of population-based colorectal cancer screening
in Canada (forthcoming).
Will BP, Berthelot J-M, Le Petit C, Tomiak EM, Verma S, Evans WK.
Estimates of the lifetime costs of breast cancer treatment in Canada.
Eur J Cancer 2000; 36: 724-35.
Will BP, Berthelot J-M, Nobrega KM, Flanagan W, Evans WK. Canada’s
Population Health Model (POHEM): A tool for performing economic
evaluations of cancer control interventions. Eur J Cancer 2001;
37: 1797-1804.
Will BP, Nobrega KM, Berthelot J-M, Flanagan W, Wolfson MC, Logan
DM, Evans WK. First do no harm: extending the debate on the provision
of preventive tamoxifen. Br J Cancer 2001;85(9): 1280-8.
Phyllis Will has recently retired after 21 years
as a public servant, including 16 years at Statistics Canada. She
continues to participate in HAMG activities (such as writing this
article) through the Statistics Canada Alumni Program. Her career
as research analyst focused mostly on social policy and health outcomes,
and she was Chief of the Modeling Section of HAMG. For over a decade,
Phyllis has collaborated with medical oncologists, cancer registry
personnel, and other researchers to develop the models described
here. She has presented these results around the world and has prepared
many manuscripts for peer-reviewed journals.
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