The American Cancer Society is one of the oldest and largest voluntary health organization dedicated to eliminating cancer in the US.
Headquartered in Atlanta, ACS has a 60-person team of expert researchers conducting large-scale nationwide cancer prevention studies. Early ACS epidemiologic studies provided some of the strongest evidence linking smoking with lung cancer and higher overall death rates. This evidence led to the Surgeon General’s landmark 1964 conclusion that smoking causes lung cancer, helping drive a decline in adult smoking rates from over 40% in 1964 to less than 20% today.
Rebecca Siegel, Scientific Director, Surveillance Research, ACS shares her views on the latest annual statistics report showing a 29% decrease in four major cancer types over the last 26 years. Edited excerpts:
A steady decline in lung cancer deaths has led to a 29% drop in cancer deaths in the US, according to the ACS report. What are the other factors, besides cessation of smoking, that have contributed to bringing down the number?
The 29% drop is driven by declines in mortality for the four major cancers – lung, colorectal, breast, and prostate. The largest contributor is the rapid steady declines in smoking since the 1960s, which causes 80% of lung cancers, but also 11 other cancer types such as oesophagus, oral cavity, liver, etc. In addition to smoking, there have been declines in the incidence of colorectal cancer, which also translates to declines in mortality. There are also improvements in the treatment of most cancer types, and early detection for some cancers like breast and colorectal, which have been known to reduce mortality.
Which are other cancers which show a declining trend in terms of mortality? Has there been any perceptible fall in their incidence as well?
All of the most common cancers have declining death rates, except liver, pancreas and uterine corpus or endometrial, all of which have increasing incidence rates as well.
The ACS report also shows that the progress in reducing colorectal, breast and prostate cancers has slowed. What are the reasons for this?
Stable death rates for prostate cancer following decades of rapid decline is probably related to the large reduction in the use of the PSA test to screen for prostate cancer and the uptick in the incidence of distant-stage diagnosis. The USPSTF and the ACS recommended against the use of the PSA test for screening in the late 2000s because of concerns about overdiagnosis and overtreatment. Many men were diagnosed with and treated for prostate “cancer” that would never have gone on to cause symptoms or harm. Slowing in colorectal cancer mortality may reflect a slowing in first-time screening. The big surge in screening was during 2000-2010 with slower increases since. And for breast cancer, it may reflect increases in incidence caused by the obesity epidemic and continued declines in the fertility rate. Fewer and later-age pregnancies increase breast cancer risk.
Although cancer survival rates have improved in recent years, the death rates continue to remain more or less steady except in certain paediatric malignancies. How will you explain this paradox?
The cancer death rates have dropped by 29% in 26 years – from 215 per 100,000 in 1991 to 152 in 2017. That is not steady. Also, survival rates are artificially inflated when cancers are detected before symptoms, such as through screening or incidentally, which is most clearly observed for prostate cancer survival rates, which approach 100% even for regional stage diagnoses.