In most developed countries, cancer mortality has begun to decline only within the last 15 to 20 years, although in Japan, death rates from cancer began falling as early as the 1960s (28-30). Of course, cancer takes many different forms, and trends vary greatly by the site of the primary tumor. Lung cancer has become more common due to increased smoking habits, while stomach cancer has been in decline. Among women, mortality due to cervical cancer has fallen dramatically thanks to successful medical intervention (screening and early treatment) while breast cancer has been on the rise apparently due to a number of interrelated factors (lower and later fertility, changes in diet, and possibly other factors as well).

It is sometimes overlooked that some common forms of cancer may be caused by infection. For example, stomach cancer is often brought on by infection with Helicobacter pylori. Infection with H. pylori, and hence stomach cancer, was especially common in Japan prior to the widespread availability of refrigeration (31,32). Liver cancer is related to hepatitis infection (both B and C strains of the virus), and, thus, reductions in liver cancer hinge on controlling infection as well as curbing excess drinking. A third example is infection by the human papilloma virus, which can cause cervical cancer (33).

These three forms of cancer have tended to decline in recent decades and should decline further as the relevant infectious agents are brought under control (e.g., hepatitis B and C). On the other hand, cancers that have become more common include those strongly influenced by individual behaviors (e.g., lung and pancreatic cancer are linked to smoking, and both have tended to increase over time) and some others whose causes are mysterious or poorly understood (e.g., breast cancer and colorectal cancer, both rising but for unknown or uncertain reasons).

As noted earlier, trends in mortality among the elderly are the main factor behind the continued increase in life expectancy in developed countries. Furthermore, the main components of mortality at these ages are CVD and cancer. These two causes have been in decline during recent decades for reasons that are complex and not entirely understood. It is clear that there are multiple causes involved in bringing down death rates due to CVD and cancer. Medical science has played a part, but so have changes in diet and personal habits as well as community efforts and economic changes that have reduced the spread of infectious agents. It is important to keep this complex causality in mind when speculating about future trends in human mortality.

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