Cancer & Longevity

Cancer & Longevity: -by David Cragin note: this page is available at http://www.phact.org/e/z/cancer.htm

Both ideas: that decreasing infant mortality helped increase longevity; and that cancer is proportionally a more important disease because we live longer, are correct - however, they only tell part of the story. A complete answer on cancer & longevity would require a very very very long answer (or a 1-semester class). Instead, I’ll try stick to the salient points. Further information is available from the excellent websites listed below.

Most of the information below has been extracted from the websites of major health organizations in the U.S. These sites offer a wealth of well-written documents and analyses of the highest credibility. In contrast, studies from non-mainstream researchers or research groups may conflict with the findings of these major research organizations. If using other sources, consider whether the individual researchers have a vested interest in their findings (and whether they’ve taken into account many of the issues raised in the following). Unfortunately, it’s easy to hype or downplay the significance of cancer by presenting partial facts. By relying mostly on the conclusions of the major health research organizations in the U.S., the following is a hopefully neutral attempt. N.B., the credibility and integrity of the research organizations listed below is hard to supersede. While I have cited studies by individual groups of authors, these researchers are affiliated with many of the same highly reputable research organizations and their research is well-regarded.

It’s correct in that some of the gains we’ve seen in life expectancy in the U.S. were due to curing diseases that caused infant (and child) mortality. Eliminating a disease that affects many infants and children has a much greater impact on average life expectancy than curing a disease that affects many old people (based on simple mathematics, i.e., averaging). Increased longevity in the U.S. also has derived from eliminating or reducing the impact of infectious diseases at all ages. For example, in 1900, pneumonia/influenza was the top cause of death, while by 1996 it had dropped to 6th. The 2nd main cause of death in 1900 was tuberculosis and now accounts for 0.05% of deaths. The 3rd main cause of death in 1900 was intestinal diseases, (i.e., diseases particularly deadly to children) and now this is a very rare cause of death (all NCHS, 1997, 1999). In general, infectious disease is most deadly to the young, the elderly, and the (already) sick.

In addition to progress on infectious diseases, we’ve recently reduced the impact of many diseases of the aged and this has also contributed to a steady rise in life expectancy. For example, while heart disease is still the #1 killer in the U.S. by far, its incidence is down 50% since the 1960s (quite a success story). Now more than half the people who get cancer live (ACS, 1999, NCHS, 1999). As the tables provided by TJ demonstrated, even a dramatic reduction like this affects average lifespans of older people by what seems a marginal amount. However, consider that even a 1-yr average difference is a lot when based on 270 million people. Another problem is that above the age of 40, risks for many diseases increase rapidly. If an older person is cured of one disease, another will sooner or late take its place.

Age & Cancer risk. Can we back up the statement that a major risk factor for cancer is age and that cancer is proportionally a more important cause of death because of our aging population? Yes. Cancer is clearly a disease of the aged. An American male has a risk of getting cancer from the age of birth to 39 yrs of 1 in 61. In contrast, for 60 - 79 yr old males, the risk is 1 in 3 (ACS, 1999). The disparity in death from cancer is even greater, because cancer survival is higher in the young (Cole & Sateren, 1995). Cole and Sateren (1995) also note that many effective cancer treatments are not 100% curative and the cancer may reoccur later in life. However, this only answers part of the question.

The best way to examine the impact of age on cancer is adjust cancer rates for both the age and the size of the population. A larger population will have more total #s of cases, so we adjust for population size. Since there are proportionally more older people now than in 1930, we either look at rates in particular age groups or also adjust the rates for the ages of the entire population. For example, comparing 1975-79 to 1987-91, death from lung cancer dropped 19% in men aged 35-54 yrs while it increased 30% in men older than 75 yrs (Devesa et al., 1995) (due to young men quitting smoking). Or using aged-adjusted population rates: in 1930, about 38/100,000 men died from stomach cancer while by 1990, about 8/100,000 died from stomach cancer (ACS, 1999). Studies on the occurrence of stomach cancer (incidence) have shown that the drop in mortality is mainly due to a decrease in incidence and not from better forms of anticancer treatments (current 5-yr survival for stomach cancer is only 21% - ACS, 1999). This tells us both incidence and mortality rates for stomach cancer are dropping. As non-cancer example - based on age-adjusted rates - from 1986 to 1996 the death rate from stroke declined 14.8 percent, but the actual number of stroke deaths rose 6.9 percent (AHA, 1999).

In contrast, lung cancer killed about 5 per 100,000 men in 1930, while by 1990 this rate had skyrocketed to 75 per 100,000 (n.b., 87% of lung cancer is due to smoking-ALS, 1999). More recently, this rate has dropped to about 71/100,000 due to lower rates of men smoking in the 1970s, 80s, & 90s (Devesa, et al., 1995, NCHS, 1999). However, since 1960, lung cancer has climbed from the 5th main cause of cancer death in women to #1 (due to increased smoking). Overall age-adjusted cancer rates, including smokers, peaked in 1990 and have been slowly dropping since (Devesa et al., 1995, Wingo et al., 1998). It’s generally accepted for nonsmokers, overall cancer rates have been dropping since the 1950s (Doll & Peto, 1981, Gold, 1998) (some specific forms have increased). If you eyeball the age-adjusted cancer death-rate graphs on the American Cancer Society website (www.ca-journal/figures/) subtract out lung cancer and recognize that some of the colon, pancreatic, stomach cancers are caused by tobacco, this becomes apparent.

One of the biggest problems in analyzing cancer rates (and many other causes of death) is accounting for the effects of smoking. Smoking has such a dramatic impact on so many forms of cancer, determining who smoked and who didn’t is key in assessing other causes of cancer and underlying cancer rates. How do you count a person who smoked for 1 yr. vs 5 yrs vs. 10 yrs - are they a smoker or a non-smoker? Do people accurately report how much/for how long they smoked? (people typically under-report bad habits). Etc?

While lung cancer is the biggest cancer killer in the U.S. and most is caused by smoking, tobacco is involved with numerous other cancers as well (ALS, 1999). Evidence suggests that tobacco causes some of the stomach, colon, rectal, pancreatic, prostate, kidney, bladder, lip, mouth, and esophagial cancers (Baron & Rohan, 1996). Also, tobacco is effective at increasing the effectiveness of many other carcinogens. For example, about 3% of the cancer in the U.S. is thought to be alcohol related, but most of this cancer risk is in smokers (Baron & Rohan, 1996, Doll & Peto, 1981). Doll and Peto (1981) also estimated that most cancer related to pollution (about 2% of cancers) and most occupation-related cancer occurs in smokers. Asbestos is a human carcinogen, but most of the people who got lung cancer from asbestos were smokers. Last year, two research groups, one in the U.S., one in the U.K., concluded that most of the cancer risk from radon is in smokers. The list of smoking-related cancers could go on & fill many pages........

The other problem with accounting for smoking is its pernicious influence on other forms of death. For example, about 2.7-times as many people die from heart disease related-to-smoking than from smoking-related lung cancer (AHA, 1999). The most important risk factor for stroke (the 3rd main cause of death in the U.S.) is high blood pressure and the risk of stroke is 5x higher in smokers with high blood pressure as in non-smokers with high blood pressure (AHA, 1999). Smoking also causes 82% of the 4th main killer in the U.S., chronic-bronchitis & emphysema (ALA, 1999). While epidemiologists have developed many techniques to account for smoking, it’s still sometimes problematic. Considering the number of people who smoke and the high rates of obesity (now 22% of the population)(obesity is the other main risk factor for the top 3 causes of death), the fact that we’ve been able to increase longevity, particularly for the aged, is amazing.

By reducing infectious disease as a significant cause of death in the U.S., we’ve picked the low hanging fruit with regards to increasing longevity. Further success in increasing longevity will likely be at a slow pace, even if we have dramatic successes. Take for example, childhood cancer. Currently for kids from 1 to 15 yrs, cancer is the 2nd main cause of death (accidents are 1st) (ACS, 1999). For obvious reasons, we want to cure childhood cancer (I have a son), but this won’t affect longevity much. In 1999, an estimated 1600 kids will die from cancer (ACS, 1999). While on a personal level, each kid matters, on a national level, where 563,100 people are expected to die from cancer in 1999 (ACS, 1999), the elimination of those 1600 deaths would only contribute slightly to national cancer statistics or longevity. (regardless, eliminating childhood cancer remains goal most would share.) The one last challenge that would give a boost to longevity would be to eliminate the 1 in 5 deaths caused by tobacco-related illnesses.

Last point on longevity and cancer: Because cancer is such a late-age(!) disease, reducing its occurrence actually has little impact on longevity. The following value will help emphasize its significance as a late-age disease. I hesitate mentioning the actual value because it seems hard to believe. Because of this, the exact page# & reference will follow so those with library access can examine the original reference themselves. In addition, I’ve checked the value with several epidemiologists who say the value is reasonable and that the reference is quite credible. Here goes - According to Schottenfeld (1996), “Total eradication of cancer by curative and preventive interventions would ultimately result in a gain of about 2.5 years in the average life expectancy in the general population, but for the one in four Americans who would have died from cancer, the gain in life expectancy would range from 10 to 15 years” (exact quote). As discussed above, 2.5 yrs appears small, but across a population of 270 million, it’s a lot of people years, and on a personal level, one year can matter much.

REFERENCES
ACS, American Cancer Society, 1999, , http://www.cancer.org/
AHA, American Heart Association, 1999, http://www.americanheart.org/
ALA, American Lung Association, 1999, http://www.lungusa.org
Cole, P., & Sateren, W., The evolving picture of cancer in America. J. Nat. Cancer Inst. 87(3): 159-160, 1995.
Devesa, S.S., Blot, W.J., Stone, B.J., Miller, B.A., Tarone, R.E., and Fraumeni, J.F., Recent cancer trends in the United States. J. Natl. Cancer Inst. 87(3): 175-182, 1995.
Doll, R., & Peto, R., The causes of cancer: Quantitative estimates of avoidable risks of cancer in the United States today. J. Natl. Cancer Inst. 66(6): 1191-1308, 1981. (An old, but still relevant reference, and probably the most comprehensive ever written)
NCHS, National.Center for Health Statistics, Centers for Disease Control and Prevention, 1999, http://www.cdc.gov/nchswww/
National Cancer Institute, 1999, http://www.nci.nih.gov/
Schottenfeld, D., Principles and applications of cancer prevention. In: Cancer Epidemiology and Prevention. D. Schottenfeld & J.F. Fraumeni (ed.). Oxford University Press. pp. 1391, 1996. Wingo, P.A., Ries, L.A., Rosenberg, H.M., Miller, D.S., and Edwards, B.K., Cancer incidence and mortality, 1973-1995. Cancer 6: 1197-1207, 1998. (March 15).

David Cragin is a member of the Philadelphia Association for Critical Thinking
He has written more on this subject at:
http://www.phact.org/phact/cancer.htm

you can email him at: DCragin@phact.org
this page is posted by Eric Krieg click for more smoking info ->