Tuesday, January 3, 2012

Medical interventions to prevent cancer


Much has been written over the past few months on progress against cancer. For example, in the New York Times, Kolata summarizes funding for cancer research and shows the percentage of health research funding spent on cancer treatment research, cancer biology, and cancer causation, with only a small fraction on early detection and prevention (1).  This reflects the commitment made forty years ago, when the U.S. declared war on cancer, and promised a cure. While treatment and biology gain the predominant funding, we should remember that there are proven ways to prevent cancer, some through lifestyle changes, and others through medical interventions. While medical interventions may most often be focused on high-risk men and women, we know that smoking cessation – a population wide strategy – can reduce both incidence of many cancers and mortality from cancer. 

Smoking cessation powerfully reduces lung cancer and total mortality as demonstrated in Figure 1. Compared to continuing smokers, those who successfully quit have a 20% reduction in lung cancer mortality within 1 to 4 years of quitting and a 40% reduction within 5 to 9 years (2). Smoking cessation also reduces total mortality by 13% in less than 5 years and by 33% in less than 10 years, due to the additional benefits of reduced risk of cardiovascular death and other smoking-related cancer deaths (2). Thus, the benefits for smoking cessation are unarguable.

On the other hand, seeking technologic solutions, the randomized clinical trial for screening smokers with CT scans, showed a 20% reduction in lung cancer mortality after an average of 6 years of follow-up, and a reduction in total mortality of 6.7% (9).
        
But there are other research-proven strategies and interventions to prevent much of cancer outright.

We might consider these as drugs (aspirin, selective estrogen receptor modulators), vaccines, and screening or surgical interventions. While the time frame from intervention to benefit varies for the cancers, most of these medical interventions result in substantial benefits and typically the benefits outweigh the risks of exposing the population to the medical procedures. For example, we estimated that a large proportion of postmenopausal women would benefit from Raloxifene (a SERM) and given its relative positive trade off of benefits to risk, its widespread use could result in a substantial reduction in postmenopausal breast cancer (3). Likewise, for aspirin which is recommended for men over 45 to reduce risk of cardiovascular disease, and for women over 55 to reduce risk of cerebrovascular disease (4), the benefits for colon and other cancer risk reduction over 20 or more years of use are substantial (5). Perhaps the reduction in cancer is an unintended benefit of widespread use to reduce cardiovascular disease risk.

Vaccines, on the other hand, more typically considered a population-wide interventions, take decades to observe the benefit of reduced cancer incidence, and require broad implementation to achieve reduction in the cancer burden for the whole population. Several countries have embarked on more traditional public health strategies for HPV vaccine (Australia, mandatory) and hepatitis vaccine programs (e.g., Taiwan) to achieve reductions in the burden of cancer.

In the table below, we summarize the target for each intervention, the magnitude of reduction in cancer that has been observed following interventions, and the source of evidence for each intervention.


Table. Proven cancer prevention interventions using medical interventions
Intervention
Target
Magnitude of reduction
Evidence
Aspirin
Total cancer mortality
20% reduction
Follow-up of 8 RCT (5)
Aspirin
Colon cancer

40%
Five RCTs (6) and RCT in Lynch syndrome (7)
SERMs
Tamoxifen
Raloxifene
Breast cancer incidence
40 to 50%
RCT (8, 9)
Salpingo oophorectomy
Familial risk of breast cancer
50%
Observational data synthesis (10)
Screening for colon cancer
Sigmoidoscopy (RCT)
Colonoscopy
Colon cancer mortality
Sigmoiodoscopy 30% to 40% in 10 years

Colonoscopy – 50%
UK RCT sigmoidoscopy  (11)

observational data
Vaccines
HPV
Hepatitis, etc
Cervical cancer
Liver cancer

(12, 13)
Mammography
Breast mortality
30%
RCT refs
Spiral CT for lung cancer
Lung ca mortality
20% in 6.5 yrs
RCT (14)

Related CNiC posts


Smoking cessation: The rapid road to preventing cancer mortality 



Literature cited



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