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11 February 2019

Half a million breast cancer deaths averted! That’s certainly a headline that will get attention. A study just published in Cancer concluded that approximately 500 million deaths from breast cancer among women in the United States (US) have been averted over the past 30 years due to screening mammography and improved therapy.

The most important point to understand about this study is that it did NOT look at every woman who was diagnosed with breast cancer since 1989 and tabulate deaths in these women – there is no such repository of data that captures every single diagnosis and death from cancer. The study was based on database analysis as well as modeling and extrapolation.

This study utilized data from the National Cancer Institute’s Surveillance Epidemiology End Results (SEER) program – which collects data on cancer diagnosis, treatment and survival for approximately 30% of the US population. Different states and counties have been added over the years to help ensure that the database reflects the racial, ethnic and socioeconomic diversity of the US. Data points are added to reflect current scientific knowledge and changes to staging systems. Current year reported numbers are estimates, as data entry and analysis lags several years. This article provides a history of the program and discusses some of the limitations.

For this study, the authors analyzed breast cancer mortality data from 1989 for women age 40-84. They concluded that cumulative breast cancer deaths averted over the past 30 years ranged from 384,000 – 614,500.

The most recent data in the SEER registry for US breast cancer incidence and deaths extends through 2015. Therefore, information from 2016 – 2018 is based on estimates and projections. They utilized 4 different models to estimate “background breast cancer mortality rates” – the likelihood of death from breast cancer without screening mammography or modern therapy. These 4 models use different assumptions about breast cancer mortality rates based on trends prior to 1989, resulting in a range in the estimated number of lives saved. The authors combined this information with US population data obtained from census reports and estimates. The authors noted that they made no attempt to separate out the effect of screening mammography versus treatment, and also noted that the SEER database did not include information on whether newly diagnosed breast cancer patients had undergone a mammogram within 1-2 years of diagnosis. In addition, they commented that only about 50% of women age 40 and over in the US undergo screening mammography every or every other year.

One of the authors, Dr. Hendrick, commented in the press release that accompanied the article that “The best possible long-term effect of our findings would be to help women recognize that early detection and modern, personalized breast cancer treatment saves lives and to encourage more women to get screened annually starting at age 40.” [emphasis mine] However, as the authors did not separate out the effect of screening mammography versus modern therapy on breast cancer mortality, the highlighted part of his conclusion does not seem to be supported by the results of this study.

Studies such as these often raise more questions than they answer. 500,000 lives saved over 30 years sounds like tremendous progress – but we know that in the US, approximately 40,000 women and 2500 men die every year due to metastatic breast cancer. A lot of the disconnect is that studies like these often report death rates, usually per 100,000 people, not absolute numbers. Treatments have improved, and screening mammography has made a difference. But as the US population is growing and aging (and the likelihood of breast cancer increases with age) there may be more individuals with breast cancer. Cancer incidence also increases with increased use of screening mammography (due to increased detection), but not all of these cancers are lethal. Rates of death from breast cancer decrease, but absolute numbers may not.

I bring up these last points not to put a damper on some of the glowing headlines regarding this study, but to ensure that we don’t lose focus regarding the work to be done. Approximately 40,000 women and 2500 men will die this year due to metastatic breast cancer. We’ve made tremendous progress, but it’s not time to celebrate just yet.

The referenced article in Cancer is behind a paywall. If anyone would like a full copy, please email me: contact at drattai dot com

9 January 2019

The American Cancer Society has just published their updated “Cancer Facts and Figures”, documenting cancer incidence and mortality rates. When combined by disease site, cancer death rates have decreased by 27% from 1991-2016, resulting in approximately 2.6 million cancer deaths avoided. From 2007 – 2016, cancer death rates have declined approximately 1.8% per year for men, and 1.4% per year for women. From 2006 – 2015, rates of cancer development increased approximately 2% per year for men and were stable for women.  It is anticipated that there will still be more than 1.7 million new cancers diagnosed and 600,000 cancer-related deaths in 2019.

The most common cancers in men are lung, prostate and colorectal, and the most common cancers in women are breast, lung and colorectal. Breast cancer accounts for 30% of all new cancer diagnoses in women.

Lung cancer is the most frequent cause of cancer-related deaths in both men and women. Much of the decline in incidence and mortality is attributed to a decline in smoking rates, but it important to note that many cases of lung cancer occur in non-smokers. Rates of new lung cancer cases have decreased by 3% per year in men and 1.5% per year in women, and these differences are not fully explained by smoking rates – especially in cases of lung cancer in younger women. In addition, while lung cancer related deaths in men decreased by 48%, women only experienced a 23% reduction in death rates. 

Improvements in screening and treatment have resulted in a decreased number of deaths due to lung, breast colorectal and prostate cancer, and breast cancer death rates decreased approximately 40% from 1989 – 2016. However, there has been a modest increase in breast cancer incidence, in part due to the association of breast cancer development with post-menopausal obesity as well as alcohol intake. 

While the prostate cancer death rate has decreased, there has been some flattening of the curve from 2013-2016. This may be related to more recent guidelines that do not recommend routine testing of the prostate-specific antigen (PSA) in patients without symptoms.

Colorectal cancer death rates declined 53% from 1970 – 2016, but in patients younger than age 55, new cases of colorectal cancer have increased almost 2% per year since the mid 1990s

Death rates in cancers related to obesity, including pancreatic and uterine cancer, have been increasing. Deaths due to liver cancer have also risen, with an increasing number of cases related to obesity rather than alcohol and chronic hepatitis.

There has been a decline in the racial gaps in mortality rates, but blacks are still 14% more likely to die of cancer compared to whites (33% 25 years ago). While this is encouraging, the economic gap is growing, especially related to cancers that have seen improvements due to early screening and treatment, improved nutrition and smoking cessation.

It was noted that cancer risk increases with age, and those over 85 account for approximately 8% of all new cancer diagnoses. Cancer is also noted to be the 2ndleading cause of death, after heart disease in this population. There may be many challenges to diagnosis and treatment in older adults due to the presence of co-existing medical conditions as well as other factors. 

It is important to note some limitations of the report. Information is gathered from several sources and data may be incomplete. The current report notes incidence rates through 2014 and survival data through 2015. 

The general downward trend in cancer incidence and improvement in survival is encouraging, but there is much work to be done.

Additional Information:
KPCC Air Talk interview with Dr. Attai
American Cancer Society Press Release
American Cancer Society “Facts and Figures”