Breast cancer expert Dr. Julie Gralow discusses metastatic breast cancer staging, including prognostic staging, breast cancer subtypes, and the meaning of metastasis.
Dr. Julie Gralow is the Jill Bennett Endowed Professor of Breast Medical Oncology at the University of Washington, Fred Hutchinson Cancer Research Center, and the Seattle Cancer Care Alliance. More about this expert here.
The staging of breast cancer has traditionally been by something we call anatomic staging, which has the tumor size, the number of local lymph nodes involved, and whether it has metastasized beyond the lymph nodes. So, that’s TNM – tumor, nodes, metastases. And so, that’s the classic staging, and based on combinations of those things, you can be a Stage 0 through Stage 4. Stage 0 is reserved for ductal carcinoma in situ, which is a noninvasive breast cancer that can’t generally spread beyond the breast, so that’s Stage 0, and then we go up for invasive cancer.
Interestingly, just a couple years ago, the big group that oversees the staging of cancers decided that in breast cancer, that TNM – the size, the lymph nodes, and the location beyond the lymph nodes – is not good enough anymore, so they came up with a proposal for what we call a clinical prognostic stage, which is a companion to the traditional TNM staging.
What they were getting at here was it’s not just how big your cancer is, how many lymph nodes, or whatever, it’s also at the biology of your cancer. So, this new clinical prognostic stage takes into account the estrogen and progesterone receptor of your cancer, the HER2 receptor at the grade, which is a degree of aggressiveness, and then, if your tumor qualifies, one of the newer genomic testing profiles that we use in earlier-stage breast cancer, such as the Oncotype DX 21-gene recurrence score or the MammaPrint 70-gene assay.
So, all of that goes into account now, and the whole point here is that the estrogen receptor, the HER2, the grade, and some of these genomics may actually make more difference than how many lymph nodes you have, where the cancer is, and how big it is, so it’s not just the size, but also the biology of the cancer that we’re trying to include in the new staging systems.
In this program, Dr. Gralow, we’re focusing on metastatic breast cancer. Would you explain when breast cancer is considered to have metastasized?
That’s a great question because technically, if the lymph nodes in the armpit – the axillary area – are involved, that does represent spread beyond the breast, but if it stays in the local lymph node areas, it’s not technically called a metastatic or Stage 4 breast cancer. So, metastatic breast cancer would have traveled beyond the breast and those local lymph nodes, and some common sites would be to the bone, to the lungs, to the liver, less commonly – at least, up front – to the brain, and it could also travel to other lymph node groups beyond those just in the armpit and the local chest wall area as well.
What about subtypes? How are they determined?
The main way that we subtype breast cancer right now is based on the expression of estrogen and progesterone receptor, the two hormone receptors, and the HER2 receptor, the human epidermal growth factor receptor. So, to date, those are the most important features when we subtype, and so, a tumor can either express estrogen and progesterone receptor or not, and it can overexpress or amplify HER2 or not, and if you think that through, you can come up with four different major subtypes, in a way, based on estrogen receptor positive or negative and HER2 positive or negative.
When all three of those are negative, we call that triple negative breast cancer, and that’s about 18-20% of all breast cancers as diagnosed in the U.S. And then, when all three are positive, we sometimes call it triple positive, and the reason that we subtype is because we know that those different subsets act differently and that we have different drugs to treat them with, and we’ve got great drugs in the categories of hormone receptor positive and HER2 positive, and increasingly, some recently hope in a new drug approval or two in triple negative breast cancer as well.