For the first time since cancer incidence has been tracked in the US, the number of people diagnosed with cancer has declined -- and the number of people dying from the disease continues to decline, following a 15-year trend. While the authors of a report in the November 2008 issue of The Journal of the National Cancer Institute attribute the decline in cancer diagnoses to improvements in prevention efforts, they caution that more needs to be done to sustain and extend this progress into all categories of cancer, as well as into all segments of the population.
Each year, the American Cancer Society (ACS), the Centers for Disease Control and Prevention, the National Cancer Institute, and the North American Association of Central Cancer Registries issue a joint report on the latest cancer trends in the US. Previous reports have noted that death rates from cancer have been declining in the US since 1991, largely due to improvements in screening, detection, and treatment.
However, this year's report found that new cases of cancer decreased an annual average of 0.8 percent for the years 1999 to 2005, the last year for which the necessary data was available. This represents the first extended decline in new cancer cases since 1971, when President Richard Nixon signed the National Cancer Act after declaring a "war on cancer" in his inaugural address.
2008 Cancer Statistics
In 2008, the ACS estimates that about 1.4 million Americans will have been diagnosed with cancer and that about 560,000 people will have died from the disease -- making it the second most common cause of death in the US after heart disease. While these survival statistics fluctuate significantly based on type of cancer and stage of disease at diagnosis, the five-year relative survival rate for all individuals receiving a diagnosis of cancer between 1996 and 2003 was 66 percent. This represents a significant increase over the 50 percent five-year relative survival rate for all cancers diagnosed between 1975 and 1977. (Relative survival is defined as the percentage of cancer patients alive five years after diagnosis compared with the percentage of cancer-free individuals of the same age, race, and sex who are still alive after the same five-year period.)
Cancers of the lung, colon, breast, and prostate account for approximately half of all new cancer diagnoses, and about 30 percent of all cancer deaths in 2008 were the result of lung cancer.
The Report's Findings
According to the report [PubMed Abstract], the number of new cancer diagnoses and death rates from all cancers combined saw overall decreases in both men and women and in most racial and ethnic categories. In general, the decline in new cancer cases and in cancer mortality is the result of decreases in the three most common cancers in men (prostate, lung, and colorectal), and in two of the three most common cancers in women (breast and colorectal). (Lung cancer is the other most common cancer in women.) The report notes that new cases of breast cancer declined at a rate of 2.2 percent per year from 1999 to 2005, and new cases of prostate cancer dropped 4.4 percent a year from 2001 to 2005.
The report's authors explain that the decline in death rates is the result of a combination of primary prevention, early detection, and new treatment advances. For instance, the increase in the number of individuals receiving improved colorectal cancer screening, which led to earlier detection, is responsible for the drop in deaths from that cancer -- cutting the death rate 4.3 percent per year from 2002 to 2005.
Lung Cancer: Gender Discrepancies
The ACS notes that the largest single factor responsible for the decrease in new cancer cases and mortality figures is that fewer Americans have taken up smoking over the last 30 years. However, while death rates from lung cancer have been decreasing in men since 1990, female lung cancer death rates have only recently begun to level off, after several decades of increases. This reflects the rise in the number of women who started smoking as adolescents in the 1960s and 1970s. In fact, for the past 21 years, more women have died annually from lung cancer than from breast cancer.
The study's authors admit that interpreting the decline in new cancer cases, known as cancer incidence, is a more difficult task than explaining the decrease in cancer mortality. Trends showing both increases and decreases in cancer incidence are often dependent on evolving changes in cancer prevention recommendations, as well as screening and diagnostic practices. Increased screening for breast cancer by mammography, for instance, may lead to an increase in the number of new breast cancers diagnosed.
Looking at changes in cancer prevention, the authors point to the sharp decline in new cases of breast cancer in 2002 and 2003. This came in the wake of a widely reported 2002 study that found hormone replacement therapy (HRT) for women increased the risk of breast cancer, which caused many women to stop using HRT as a treatment for the unpleasant effects of menopause.
In general, however, experts theorize that the drop in new cases of cancer may be partly attributable to the adoption of healthier lifestyles.
Some Cancers on the Increase
Not all the report's findings were positive. The number of new cancers being diagnosed in men increased for cancers of the kidney, liver, and esophagus, as well as for leukemia, non-Hodgkin lymphoma, myeloma, and melanoma. For women, diagnosis figures increased for cancers of the lung, bladder, kidney, thyroid, pancreas, brain, as well as for leukemia, non-Hodgkin lymphoma, and melanoma.
The report also noted that while significant strides have been made against smoking and lung cancer, the national obesity epidemic is a serious cause for concern. In addition to increasing an individual's risk for developing diabetes and heart disease, obesity has been linked to increased risk for a number of cancers.
