20 July 2015

This is not a new question, and I promise there will be many parts to this story. The latest: Breast Cancer Screening, Incidence and Mortality Across US Counties, published in the July 2015 issue of JAMA Internal Medicine. The authors of the study noted that rates of early breast cancer detection have increased with the widespread use of screening mammography, but death rates from breast cancer have not decreased, leading to the conclusion that many breast cancers are “overdiagnosed”.

One would expect that if there were an increase in the number of early breast cancers detected due to screening mammography, fewer women would subsequently die from breast cancer. Isn’t early detection the key to survival? A reasonable question that is raised from this study is “What is the value of screening mammography?”. First, several points:

  1. The authors noted that the rates of early breast cancer, especially DCIS, have increased significantly with the widespread use of screening mammography.
  2. It is well known that some breast cancers have such an indolent biologic behavior that they will never become a threat to a breast or to a life.
  3. The more we screen, the more we find. Not everything needs to be found.
  4. Finding indolent lesions is considered “overdiagnosis”. Treating these lesions with traditional surgery, radiation and other treatments is considered “overtreatment”.
  5. Early detection does not always equal cure. Some breast cancers have a very aggressive behavior, and may prove to be fatal even when diagnosed in early stages.

Before you cancel your upcoming mammogram, appointment, some limitations of the study were pointed out in an accompanying editorial: Effect of Screening Mammography on Cancer Incidence and Mortality. One of the biggest criticisms is how the study was actually conducted, using the “ecological method”, which studies large groups, not individuals. It is not possible to tell if the women who were diagnosed with breast cancer are the same ones that subsequently died due to the disease. Other limitations of this of study are that no information is available on tumor subtypes or adjuvant therapy (chemotherapy, hormonal therapy and radiation). Another limitation of the study is that it evaluated data over a 10 year period, which might not be long enough to have an impact on survival rates. Finally, it was discussed that there was the potential for “confounding bias” – factors associated with an increased risk of breast cancer might also be associated with an increased rate of obtaining screening mammograms. [For a good discussion of the types of bias that may be present in research studies, review this article from HealthKnowledge.]

There is no question that we are finding more early stage breast cancers, including DCIS. There is much debate on whether or not DCIS even represents “cancer”. But the reality is that while we recognize that not all cancers will progress, we do not yet have the ability to predict the behavior of a cancer with certainty for an individual woman. We do not yet have that crystal ball.

So now what? The conclusion always seems to be “ask your doctor”. But physicians do not have all of the answers. What is clear is that the decision to begin or continue screening mammography is no longer automatic – discussion about the benefits of mammography, the potential harms, a woman’s own risk tolerance, and personal beliefs is necessary – this is the essence of shared decision making.

Various online tools have been developed to help women make more informed decisions. One is Weill Cornell Medical College’s Breast Screening Decisions, meant to be used by women in their 40’s. This is a start. We also need to develop that “cancer crystal ball”, which will allow us to more accurately predict who will develop cancer, and the behavior of a cancer that has developed. We’re just not there yet. Stay tuned as this is certainly not the last word on this issue.

30 March 2015

Annual Report to the Nation on the Status of Cancer, 1975-2011, Featuring Incidence of Breast Cancer Subtypes by Race/Ethnicity, Poverty and State

Today, the Journal of the National Cancer Institute (JNCI) released a report reviewing cancer data, specifically breast cancer, from 1975-2011. For the first time, data regarding breast cancer subtypes was included in the report, and incidence of breast cancer subtypes by age, race/ethnicity, poverty level, and other factors are included. The following summarizes some of the information found in the report.

It is well known that breast cancer is not one disease. There are 4 primary molecular subtypes based on hormone receptor (HR) status (commonly reported as ER / estrogen receptor and PR / progesterone receptor) and Her2/neu status. The subtypes are:
– Luminal A: HR+ / Her2 negative; 72% of all breast cancers
– Luminal B: HR+ /  Her2 positive; 10% of all breast cancers
– Her2-enriched: HR- / Her2 positive; 5% of all breast cancers
– Basal-like / Triple Negative: HR- / Her2 negative; 13% of all breast cancers

The report demonstrated that there are some unique patterns breast cancer subtype related to race/ethnicity, poverty level, and geography.
– HR+ / Her2- breast cancer is considered to be the least aggressive subtype. Rates of this subtype were highest in non-Hispanic white women. The rates of this breast cancer subtype decreased with increasing poverty levels for every racial and ethnic group. This subtype of breast cancer also correlated strongly with use of screening mammography.

– In women younger than age 45, HR+ / Her2 negative breast cancer rates are comparable among racial / ethnic groups, but for older women this subtype was seen more often in non-Hispanic white women.

– Non-Hispanic Black women had the highest rate of HR- / Her2 – (triple negative) breast cancer, which has been known for some time. However, as triple negative breast cancer is less common than HR+ / Her2 negative disease, more women had the latter subtype. The report also confirmed that this population had the highest rates of late-stage disease and of poorly differentiated pathology (indicates more aggressive tumor behavior)  regardless of molecular subtype, and the highest rate of breast cancer deaths.

Overall trends in incidence and death rates from cancers were also noted in the report. Lung cancer remains the leading cause of death among both men and women. Black men had the highest cancer death rate of any racial or ethnic group. Lung, prostate and colorectal cancers were the leading causes of cancer death among men except in the Asian / Pacific Islander group where the leading causes were lung, liver and colorectal cancer.

Among women, the leading causes of death were found to be lung, breast and colorectal cancers. For both men and women, death rates for the 3 most common cancers declined. Exceptions were American Indian / Alaska Native men, lung cancer in Asian / Pacific Islander women (stable death rate) and colorectal cancer in American Indian / Alaska Native women (stable death rate). Death rates for liver, pancreatic, soft tissue and uterine cancers as well as melanoma were also reported. There are racial / ethnic differences present for these types of cancer as well.

There are many factors contributing to cancer incidence and death rates including race / ethnicity, socioeconomic status, geographic location and more. Reporting cancer incidence by subtype will give more insight into population-based factors, and will hopefully lead to innovative solutions  to the growing problem of disparities in cancer incidence and outcome.

Additional information from the National Cancer Institute.