With the American Cancer Society releasing new mammography screening guidelines, I have been drawn to articles exploring the big picture of how we currently think about breast cancer.
The first, a Perspective published October 29, 2015, in the New England Journal of Medicine by Gilbert Welch, MD, MPH, who has written extensively about problems with assessing benefits of cancer screening, compared trends in diagnoses of metastatic breast and prostate cancer from 1975 to 2010. These were cases that were initially diagnosed as metastatic, not instances where the cancer had been treated and recurred.
As Welch explains, William Halsted, the father of modern surgery and the radical mastectomy, believed cancer starts in an organ, slowly grows over time, eventually travels to the local lymph nodes and then metastasizes to other parts of the body. This hypothesis formed the basis for screening and early detection, because it suggested that if you could find and remove the tumor before it had a chance to spread, then the cancer would be cured.
If this theory was true, then breast cancer screening with mammography and PSA testing for prostate cancer should find more early-stage tumors as well as decrease the number of people who are first diagnosed with metastatic disease.
But take a look at the graph Welch published. It shows that the number of new cases of metastatic prostate cancer diagnosed per year since the initiation of the PSA test in 1988 decreased by half. On the other hand, the number of new cases of women being first diagnosed with metastatic breast cancer has been stable since 1975, with no decline from the increased use of mammography. What can we learn from this observation?
First, maybe not all breast cancer follows the Halsted model that we breast surgeons hold so dear. There seems to be a constant percentage of tumors that are destined to become metastatic rapidly and don’t sit around long enough in the breast to allow screening to make a difference. The good news is that the number of these cases is stable. We are not seeing an increasing number of women being diagnosed with these types of tumors. The mean (average) age of women being diagnosed with breast cancer over 40 has not changed in the past 37 years. It remains about 63.7.
Welch suggests this supports an alternative hypothesis suggested by Bernard Fisher, the breast surgeon who challenged Halsted’s radical mastectomies. Fisher believed many invasive breast cancers have already sent cells from the breast to other organs by the time the disease is detectable. Fisher’s hypothesis is the underpinning for the systemic treatments—hormonal therapies, targeted therapies, chemotherapy—that we give after surgery. We use these therapies to get to those renegade cells that may have left the breast because we know that even though we can’t see them there is a reasonable chance that they are there.
Prostate cancer, however, shows a completely different pattern. In that case, Welch explains, PSA testing caused a big increase in prostate cancer diagnoses when introduced in the early 90’s but—unlike with breast cancer—the number of men being first diagnosed with metastatic prostate cancer has plummeted. This means that prostate cancer does often behave more like Halsted predicted, spreading in a nice orderly fashion that allows for earlier detection and cure. But this decrease in an initial diagnosis of metastatic disease does not always decrease the chance of later death from prostate cancer. Some of these “early” cases have also already seeded the rest of the body, just as Fisher suspected.
Sam Hellman, a radiation therapist I knew in Boston, suggested a third explanation. Maybe cancers can behave in different ways. There are some that spread early, before they are clinically detectable. These types of cancers get minimal benefit from “early detection” but, as Fisher predicted, do benefit from systemic therapies. But there are also other women with the slow, plodding, well-differentiated cancers. And it is these women who may well benefit from screening.
My biggest insight from all of this: By lumping all breast cancers together when we talk about screening, we have set the stage for the “Guideline Wars” that lead women who are diagnosed with metastatic disease to feel guilty that it must be their fault for not getting screened enough or early enough and women with DCIS to wonder if they should have had screening in the first place.
I think it is time to stop fighting about this and move to a better understanding of how breast cancer starts and how to prevent it. Many of you have heard me cite cancer of the cervix. When I became a surgeon, women who had an abnormal Pap smear often underwent a total hysterectomy, losing their fertility. Then it was recognized that a local surgery or a biopsy was often was enough to remove the cancer. Once human papillomavirus (HPV) was identified as the cause, we could develop a vaccine to prevent cervical cancer. This means our daughters probably won’t even know anyone with cancer of the cervix.
We can do this for cancer of the breast, too. We have to. Our lives and the lives of our daughters and granddaughters depend on it!