Cancer Epidemiology, Prevention, and Survivorship

Introduction

Cancer epidemiology provides the tools and methods to understand the cancer problem in any given population, from the local level up to the global level. Incidence, prevalence, and mortality are the most commonly used measures to assess the cancer burden. Examining temporal trends in these measures or comparison of these measures between states, regions, or countries can uncover important causes of cancer. The study of cancer from an epidemiological perspective has uncovered numerous causes of cancer and has hence paved the way towards prevention and early detection. Perhaps the most well-known accomplishment of cancer epidemiology was the identification of tobacco as a cause of lung cancer in 1964. This finding revolutionized our understanding of cancer, as it was the first time that a common, modifiable behavior—tobacco smoking—was shown to result in cancer, and subsequently led to the development and implementation of a wide range of preventive measures throughout the second half of the 20th century that have demonstrably reduced both the use of tobacco and deaths from lung cancer. ^, This chapter reviews and summarizes the latest data on the most basic measures of the global cancer burden and then briefly describes cancer prevention and early detection recommendations, as well as survivorship care.

Cancer Epidemiology

Cancer incidence and mortality are defined as the number of new cancer cases and deaths, respectively, that occur in a given population over a specified time period. The selection of the time period is arbitrary, although often these measures are expressed as an absolute number of new cases or deaths per year. While this may be helpful for planning health services in a given population, this simplified expression does not provide risk information, and it does not allow for comparisons of incidence and mortality to be made among different populations. For these uses, incidence and mortality are generally expressed as a rate or proportion of the number of new cancer cases or deaths over the number of persons at risk of developing or dying from cancer during a specified time period per 1000, 10,000, or 100,000 individuals. Often, incidence and mortality will be reported as an “age-standardized rate” (ASR) to facilitate comparisons among populations that have different age distributions.

The number of new cancer cases and deaths are captured by population-based cancer registries oriented toward a geographic or geopolitical area, such as a country, although these registries typically capture just a small proportion of the global population. Coverage also varies by country. Population coverage is typically greater for mortality than for incidence. Sometimes incidence and mortality rates are estimated in cohort studies. Cancer incidence and reporting can be influenced by the screening practices, diagnostic intensity, and primary prevention programs in the population under study. Cancer mortality data are influenced by the adequacy of death certification, including autopsy rates, by changes in cancer treatment effectiveness, and by the availability of prevention programs in the population under study.

Cancer prevalence is defined as the number of cancer cases in a population at a specific point in time over the number of persons in the population at that time point. Unlike the incidence rate, prevalence is not a measure of cancer risk. Nevertheless, it can be useful for planning health services. Ascertaining the prevalence of cancer can be done through population-based cancer registration or estimated from cross-sectional studies. Determinants of cancer prevalence include the incidence and prognosis of the cancer in question, as well as mortality from other competing causes.

Cancer survival is defined as the proportion of cancer patients surviving for a specified time after diagnosis. Despite numerous limitations, it is considered the best available measure for evaluating the effectiveness of cancer treatments. Survival is influenced by the natural history of the disease, the stage at diagnosis, and therapeutic efficacy. Survival data require long-term follow up of large number of patients, are sensitive to both the misclassification of the cause of death and to lead-time bias, and provide no insight into the quality of life lived. There are various measures of survival, each serving a different purpose and each with its own limitations. Observed survival is the probability of surviving for a specific time period, generally starting at the date of cancer diagnosis, and considers all causes of death. Corrected or cause-specific cancer survival excludes deaths due to causes other than the cancer of interest and therefore is a more valid estimate of the excess death due to a cancer. Relative cancer survival compares the observed survival of a group of cancer patients to the expected survival of a group from the general population with the same age and sex ­distribution.