1
Cancer Epidemiology

- Sun Tzu

Cancer is not a new disease. Humans are not the only species to get cancer. In fact, cancer is found throughout the animal kingdom. Therefore, hominids were likely to have suffered from cancer before the advent of Homo sapiens.

The history of cancer is evidenced by traditional medicines used by many cultures around the world. These "folk remedies" actually serve as the basis of many medical treatments used today. Many of these natural products are discussed in subsequent chapters of this book.

Perhaps the earliest reference to cancer can be found in the writings of the ancient Egyptian physician Imhotep from around 2600 BCE (see Figure 1.1). In papyrus documents dating from this period, Imhotep describes treating breast tumors with cauterization. The procedure was evidently less than successful since he instructs the reader, "Tumor against the god Xenus . do thou nothing there against." Unfortunately, even today we are left with questions about whether side-effects of some treatments are worse for patients than the disease.

Regardless of its history, cancer is a huge problem today, and is likely to become an even larger problem tomorrow. About 14 million people were diagnosed with cancer in 2012, and 18 million in 2018. This trend is daunting, with the number of new cases expected to reach 24 million by 2035.

1.1 Cancer Incidence and Mortality

Over 14 million people around the world are diagnosed with cancer each year, and this number is expected to rise. By current estimates, more than one in three people will develop a form of cancer at some point in their lifetime. Around 10 million people died from cancer in 2018. Thus, cancer kills an average of over 15 people every minute. A comprehensive understanding of cancer incidence and outcomes is an important step toward decreasing these numbers.

Figure 1.1 Statue of the Egyptian physician Imhotep (ca. 2600 BCE).

Source: https://upload.wikimedia.org/wikipedia/commons/d/d2/Imhotep.JPG.

Cancer incidence, defined as the number of new cases arising in a period of time, is gender and age specific. In males, prostate cancer is the most prolific, where over 1 million new cases were diagnosed in 2018, accounting for around 8% of all new cancer cases and 15% of all new cancer cases in men. In females, breast cancer continues to be the most common tumor type. Over 2 million new cases were diagnosed in 2018, making it the second most common cancer. Breast cancer represents about 12% of all new cancer cases, and 25% of all cancers in women.

Cancer incidence may be further defined by the lifetime risk of developing the disease. For instance, in females, the risk of developing breast cancer is 1 in 8. In males, the risk of developing prostate cancer is 1 in 6; however, 80% of men who are 80?years old are likely to have some stage of prostate cancer. Some other tumor types also show considerable gender-related differences in cancer risk. For example, males are over twice as likely to develop lung cancer as women worldwide. However, lifestyle can be a factor for some of these differences. For instance, the chance of women getting lung cancer increases in countries such as the USA where women are more likely to smoke tobacco than in some other regions of the world.

Figure 1.2 Worldwide cancer incidence by age. Statistics are shown for 2012.

Source: Data from http://gco.iarc.fr/today.

Figure 1.3 Cancer rates over time. Invasive cancers from SEER 9 areas (San Francisco, Connecticut, Detroit, Hawaii, Iowa, New Mexico, Seattle, Utah, and Atlanta) age adjusted to 2000 USA population.

Source: Data from http://gco.iarc.fr/today.

In general, cancer risk increases with age, as shown in Figure 1.2. For example, less than 50 people per 100?000 under 39?years old were diagnosed with cancer in 2012. This number increased to over 1800 people between 40 and 64?years old, and over 3500 people older than 64?years. The rate of diagnosis in males 65?years or older rises most sharply with an incidence of over 4700 per 100?000.

Cancer is a major public health problem and is expected to become even worse. Cancer incidence rates have been steadily increasing over time. This is true for both males and females. However, regional spikes and dips can be seen in trends over time. For example, a spike in male cancers is seen in the 1990s in some areas of the United States, as shown in Figure 1.3. This spike has ebbed but incidence is still higher now than it was 40?years ago. In contrast, female cancer incidence has steadily climbed in these same areas over time.

Incidence rates of some types of cancer appear to be increasing more than others. Sites with annual cancer incidence increases of 1% of more include melanoma, renal, thyroid, pancreas, and liver. Meanwhile, although incidence rates are less than 1% per year, cancers such as non-Hodgkin lymphoma, certain childhood cancers, leukemia, myeloma, testicular, and oral cancers are still on the increase. Cancer is the second leading cause of death in the USA and UK (behind heart disease). In fact, cancer causes about 25% of all the deaths in these countries.

Figure 1.4 Cancer incidence and mortality by tumor site. Numbers from IARC member countries (Germany, France, Italy, United Kingdom, USA, Australia, Austria, Belgium, Brazil, Canada, Denmark, Finland, India, Ireland, Japan, Norway, Netherlands, Qatar, Republic of Korea, Russia, Spain, Sweden, Switzerland, and Turkey) are shown for 2012.

Source: Data from http://gco.iarc.fr/today.

There are more than 200 different types of cancer but four particular tumor types constitute over half of all new cases diagnosed: breast, lung, colorectal, and prostate. In 2012, there were 14.1 million new cases of cancer diagnosed worldwide. As shown in Figure 1.4, these four cancers account for nearly 50% of these new cases (6.9 million), and are responsible for about half of all cancer deaths.

1.2 Childhood Cancer

Cancer in children is relatively rare. Less than one out of 1 million cancers are found in children under 15?years old. Nonetheless, children do get cancer. In 2012, over 160?000 children were diagnosed with cancer, and cancer killed about 80?000 children.

Leukemia is the most common form of pediatric cancer, followed by lymphomas and cancers of the central nervous system. These cancers were responsible for about 8 million deaths of children under 15?years old around the world in 2012. As shown in Figure 1.5, 35% of these deaths were caused by leukemias, compared to 12% by lymphomas and 14% by brain tumors.

Figure 1.5 Childhood cancer incidence and mortality by tumor site. Worldwide numbers for males and females up to 14?years old are shown for 2012. * All cancers exclude nonmelanoma skin cancer.

Source: http://gco.iarc.fr/today, August 2014.

Although pediatric cancers are rare compared to adult cancers, they can be devastating. Whereas adult patients who remain cancer free for five years are often considered to be "cured" since their chance of mortality after this time is consistent with other causes, this is not the case with children. Pediatric cancer patients can undergo remission only to have cancer emerge again at a relatively young age. Thus, consequences from childhood cancers can be especially brutal.

1.3 Global Epidemiology

Cancer is a global problem, but it is a larger problem in some countries than in others (Figure 1.6). North America, western Europe, Australia, and New Zealand have the highest incidence, while India, along with some countries in the Middle East and Central Africa, have lower incidences. These differences can result from population demographics and lifestyle factors. Age is also a primary risk factor. For example, India has a median age of 27?years, while the median age in the USA is 38?years. This difference in age demographics may account for the higher cancer incidence in the USA compared to India, though other factors such as a chemopreventive diet and exercise may also affect cancer incidence. For example, although Japan has a relatively high median age of 48?years, its cancer incidence rate is lower than that of the USA. This relatively low cancer rate of an elderly population has been attributed to the chemopreventive properties of soy beans and other foods in the Japanese diet.

Figure 1.6 Cancer incidence and mortality by country. Incidence (top) and mortality (bottom) per 100?000 people for all cancers are shown for 2018.

Source: http://gco.iarc.fr/today.

Overall, cancer mortality rates correlate with incidence, an effect shown in Figure 1.6. However, some intriguing observations arise from these comparisons. For example, the demarcation line between North and South Korea appears to delineate a...