Still, huge challenges remain. Many people who should be screened for the disease are not. America’s obesity epidemic is a grave concern, since obesity is associated with several types of cancer. Last year, cancer cost the nation $189.5 billion, according to National Institutes of Health estimates. This year, there will be about 1.37 million new cancer cases diagnosed, and more than half a million people are expected to die. NEWSWEEK’s Laura Fording spoke with Dr. Michael Thun, who heads epidemiological research for the American Cancer Society, about the report’s latest findings.
NEWSWEEK: You say there is good news and bad news in this report.
Dr. Michael Thun: The good news is there is a decline in the death rates from all cancers, and specifically declines in lung cancer, prostate cancer and colon cancer death rates in men. Death rates for breast cancer and colon cancer in women have also decreased, and there has been a leveling of the lung cancer death rate in women. The bad news is that the incidence of certain cancers, or the rate of new diagnoses, continues to increase. For example, in 1975, for women of all races, the incidence of breast cancer was 105 per 100,000 people. It had increased by 1998 (the last year for which this data for breast cancer is complete) to 140.3 per 100,000.
How do you explain it?
For breast cancer, the rate of increase was faster during the early 1980s than it has been lately. That’s because several things happened at the same time. The reproductive patterns of women changed–they began having fewer children later, which increases the number of menstrual cycles. Mammography was introduced, so the detection of breast cancers that might not have been found, or found later, grew. In recent years there has been widespread use of post-menopausal hormones as well as an obesity epidemic. All of theses things contribute to a greater incidence of breast cancer. But detangling these factors is difficult.
According to the report, death rates for heart diseases and cerebrovascular diseases have dropped significantly since 1950. But the death rate for cancer has remained relatively unchanged. Can you explain?
We’ve made less progress in reducing mortality from cancer than the huge gains we made with respect to cardiovascular diseases. But the trend in cancer did turn a corner in the early 1990s and has been going down.
The drops in death rates sound fairly significant. Is there an explanation?
For some cancers we do, but not for others. The downturn in lung cancer in men and the leveling off in death rates in women is due to past reductions in cigarette smoking. The downturn in breast cancer death rates reflects a combination of early detection and improvements in treatment. Similarly, the downturn in prostate cancer mortality in men can be attributed to a combination of early detection and improvements in treatment.
What other cancers are on the rise?
Some are relatively uncommon cancers: Adenocarcinoma of the lower esophagus has been on the increase, particularly in white men. This is felt to be largely related to the obesity epidemic. Smoking causes cancer of the top part of the esophagus–that has been on the decrease. The presumed reason is that obesity increases such conditions as reflux of stomach acid and bile, chronic inflammation and Barrett’s esophagus. There has also been an increase in the incidence in liver cancer, partly thought to result from increasing occurrences of chronic hepatitis C. It’s contracted mostly through blood and sex. But a second factor [in liver cancer] is obesity. Obesity can cause [a condition called] ‘fatty liver.’ A remarkable percentage of the U.S. population, some 20 percent, meet the criteria of having fatty liver. Fatty liver can result in chronic hepatitis. It’s one of the most common ways to get hepatitis nowadays. And a fraction of those people develop liver cancer. It was strongly associated with obesity in the large American Cancer Society study published last spring in New England Journal of Medicine.
Prostate cancer had a big surge in incidence in the early 1990s.
That peak corresponds to the introduction of PSA [prostate-specific antigen] screening and a tremendous increase in diagnosis of disease. Melanoma incidence has also been increasing, particularly in whites. But death rates for melanoma have been relatively flat. It’s a case where early detection is key. Other cancers: kidney, thyroid, testes. The increases are less well understood.
What’s being done to fight obesity’s role in cancer?
It has become obvious that the obesity epidemic is causing a huge burden of disease as well as health care expenditures. We are just beginning a very long process of identifying what can be done at the policy level and at the community level and in the treatment of obesity. We have been fighting the tobacco epidemic for half a century. The obesity situation really dawned on the public in the past five years.
Does obesity play a role in any other cancers?
Post-menopausal breast cancer. Fat tissue produces estrogen and estrogen causes breast cells to proliferate. The American Cancer Society study found obesity to be associated with about 10 - 12 cancers, depending on males or females. That study estimated that up to 20 percent of all cancer deaths in women and up to 14 percent in men may be attributable to current obesity patterns. So the obesity story is far from complete. Obesity and physical inactivity are the major risk factors which are going in the wrong direction.
As more people actually survive these cancers, what is their quality of life?
That’s a really important issue. It’s important to monitor these trends so that what is already known about preventing cancer or detecting it earlier and treating it appropriately can be applied. Indicators need to be developed, particularly for prostate and breast cancer, so [the medical community can] distinguish which cancers need aggressive treatment and which deserve watchful waiting.
You’re talking about the decision of what types of treatments to use, whether a person should have surgery, or chemotherapy or radiation treatments, based on their particular type and stage of cancer. The effects from the treatment itself can affect a person’s future quality of life tremendously.
Absolutely. There can be complications from surgery, or from radiation treatment. The harms caused by unnecessary treatments are always of special concern. For example, in prostate cancer, a substantial percent of cases identified by PSA testing may not be clinically aggressive. If one can identify the cases that are unlikely to progress, and just watch them carefully, then complications from treatment can be prevented. It would be very reassuring to have a sense of how aggressive one’s cancer was.
Is that difficult to gauge?
There’s a lot of work going on studying the molecular characteristics of tumors in relation to tumor recurrence, survival, metastasis, etc. Some quality of life issues pertain to getting high quality treatment in a timely fashion. [And there are] inequalities in access to care, screening and health insurance. These factors affect prevention, early detection, appropriate timely treatment, and supportive care.
What about the relationship between smoking and the reduction of lung cancer? From your report, it sounds like fewer people now smoke, and the people who continue to smoke are smoking less overall.
In 2002, cigarette consumption per person was less than half what it was in its peak level back in 1963. It continues to fall, as does the percentage of adults and kids who continue to smoke. So there is progress in both areas. But the job is not over. Twenty-eight percent of high school students still start smoking. There have been efforts to increase the price of cigarettes by raising excise taxes, to implement clean air laws and to increase the availability of treatments for people who are dependent on tobacco. But there’s tremendous room for more progress.
Have the increases in sales taxes on cigarettes have made any impact on how much people smoke?
There have been a lot of studies that show that an increase in the price of cigarettes results in a reduction in consumption. It affects price-sensitive subgroups–like kids–more.
How have environmental pollutants affected the increased incidence of cancer?
In highly exposed populations, for example, in occupations that have had very high and very long exposure [to carcinogens], there are clear increases in cancer risks. But it’s much harder to show in the general population …The American Cancer Society tries to focus cancer control efforts on the factors that will have the largest impact on cancer, which is why there has been a 50-year battle on tobacco and now this interest in obesity. There continues to be substantial research on how pollutants at different times of life may affect specific cancers.
Why do more whites than blacks survive a cancer diagnosis?
Things that affect survival are stage of diagnosis, access to treatment and quality of treatment. For poor people, setting aside race, access to early diagnosis, to prompt and high quality treatment, is substantially worse than it is for people who have health insurance or who have more financial ability to get those things. That is thought to be a very large factor. Whether biological factors also play a role is not clear. But the thinking is that a lion’s share of these disparities are coming from economic and social factors rather than biological.
The lifetime probability of developing cancer for men is 1 in 2, and for women it’s 1 in 3. That’s seems pretty high. Actually, it’s a bit disturbing.
The reason why it’s so high is that people are living longer, and for most cancers, the risk increases enormously with aging. And these probabilities include cancers which may not affect a person’s longevity or quality of life. We’re talking about the probability of developing cancer, not dying from it.
