Research to improve breast cancer detection and patient outcomes
Globally, breast cancer is the most common cancer for women and a leading cause of cancer death, according to the Breast Cancer Research Foundation. At Penn Medicine’s Abramson Cancer Center 2-PREVENT Translational Center of Excellence (TCE), experts are making important strides in detecting breast cancer recurrence early, with the goal of enabling the right prevention therapies to ultimately help patients become and remain cancer-free.
This TCE, the first and only center dedicated solely to the research of breast cancer recurrence, brings together both basic and translational laboratory investigators, like Elizabeth Chislock, PhD, and Lewis Chodosh, MD, PhD, and clinical researchers, like Angela DeMichele, MD, MSCE, a breast cancer oncologist who serves as the principal investigator for numerous clinical trials.
We sat down with Dr. Chislock to share more about how her team hopes their research will revolutionize the ability to identify and eliminate microscopic cancer cells that survive therapy to prevent breast cancer recurrence.
What are you studying and what impact do you ultimately hope to have for patients?
We're aiming to transform the way breast cancer survivors are treated coming out of their initial therapy by improving screening, so that we can better identify those who are at increased risk of recurrence and can then use therapies that target the specific biology of the disseminated tumor cells (DTCs) that have survived the initial therapy in order to eliminate these cells and prevent tumor recurrence.
Over the past couple of decades, there have been marked improvements in the ability to treat a patient's initial breast cancer. Five-year survival rates, especially for those that are caught at earlier stages, are quite high. However, up to 30% of breast cancer patients—nearly 4 million men and women in the U.S. alone—whose primary tumors appear to have been successfully treated, will ultimately suffer recurrence (their tumor coming back) often at distant or metastatic sites throughout the body. The problem is that most of those recurrent breast cancers are resistant to therapy and therefore are responsible for most breast cancer–related deaths, and there is no test to accurately determine which patients will recur and which will not. Patients have routine screenings with their clinicians, but current imaging methodologies aren't sensitive enough to be able to detect microscopic residual tumor cells that have survived therapy; they can only detect the later stage when a recurrent tumor has actually developed.
In Dr. Chodosh’s lab, we are studying that intermediate stage, where patients have undergone therapy for their breast cancer but may still harbor cancer cells that survive therapy and exist in a dormant, nonproliferating state for months, years or even decades prior to resuming growth. We see that dormant period as a therapeutic window of opportunity. With a test we developed in our lab called the DTC-Flow assay, we’re looking to screen survivors for DTCs within the bone marrow, not only to identify patient samples at increased risk of recurrence but also to isolate and characterize the various biological properties of those cells to figure out how we eliminate them. Ultimately, if we can eliminate those cells, it should be possible to prevent breast cancer recurrence.
If this research is successful, we envision a proactive and personalized treatment approach for the millions of breast cancer survivors who are at risk of recurrence by developing a sensitive method to detect those patients who have disseminated tumor cells, as well as a better understanding of which disseminated tumor cells are likely to give rise to a recurrent metastatic tumor, and what therapies can prevent that from happening.
How have technological advances enabled you to get the insights you need to do your research?
There have been multiple improvements—especially the BD technology that we've had access to—that's really enabled this to happen. One issue in trying to find DTCs is that they're incredibly rare—rarer than one tumor cell in a million bone marrow cells.
Currently, to find DTCs in bone marrow, you would have to use a test called an immunohistochemistry (IHC) assay, which basically looks at protein expression in these cells and allows you to examine one characteristic of the cells at a time. Specifically, the IHC assay looks for expression of proteins called cytokeratins, which are expressed in breast epithelial cells but are not normally found in bone marrow. Using this method, a pathologist would have to visually screen multiple slides with bone marrow cells on them trying to find a single tumor cell. It's a very labor-intensive method with a lot of cell loss, that is challenging for a pathologist to read and that is difficult to scale up. In that vein, we have benefited from BD’s development work on a pre-enrichment device coupled to fluorescence activated cell sorting (FACS) that allows us to remove many of the ‘normal’ bone marrow cells that we’re not interested in and process our sample without many of the of hands-on manipulations that lead to the loss of rare cells.
Combining that with the power of flow cytometry and cell sorting to look at multiple different properties of cells simultaneously, we're able to capture a larger range of different types of breast cancers and DTCs than we otherwise would have been able to, to scale up and screen through more bone marrow cells and, hopefully, to achieve higher sensitivity for finding these ‘needle-in-the-haystack’ cells and identifying those patients at higher risk of recurrence.
What have your clinical trials revealed so far?
Initially, Dr. DeMichele and her clinical research team wanted to determine whether it was feasible to ask patients to come in for multiple bone marrow aspirates over time, and she found that they are quite willing to do this. The current clinical trials being conducted in the 2-PREVENT TCE look at patients who are less than five years out from their initial diagnosis but have completed their primary therapy.
As part of a screening trial, called PENN-SURMOUNT, survivors can come in annually for a bone marrow aspirate for clinical screening using the standard IHC assay. Survivors who screen negative can come back for annual screenings, while those who screen positive for DTCs are offered enrollment into an interventional trial, CLEVER.
CLEVER places patients on one of three different therapeutic ‘arms’ using drugs that have been shown in mouse models of breast cancer to reduce the number of dormant residual tumor cells that survive initial therapy and to either delay or prevent tumor recurrence: one with the autophagy inhibitor hydroxychloroquine, one with the mTOR pathway inhibitor everolimus, and one that’s the combination of those two drugs.
We monitor DTC numbers over time as an indicator for whether the therapy is working and watch for recurrences down the line. We also are looking to see whether you can treat with these drugs for this length of time without toxicity. The initial findings of the trial suggest this approach is promising, but we won’t know the results until the trial has concluded.
The majority of planned patients have been enrolled on the CLEVER trial, and Dr. DeMichele and her colleague Dr. Amy Clark are gearing up for multisite trials looking at a larger population of breast cancer survivors with a focus on therapeutic effects as well as a direct comparison of our DTC-Flow assay with the current DTC-IHC assay. We anticipate that this next trial will provide valuable information on how well the DTC-Flow assay performs and how much utility this test might ultimately have.
Has anything you’ve found in the trial so far surprised you?
When we started our work, it was surprising how complicated it can be to work with bone marrow. Certain breast cell markers have been used a lot in the literature, in particular for people who are looking at circulating tumor cells (or CTCs) in the bloodstream. Surprisingly, we’ve found that there is a population of normal bone marrow cells that also express these ‘breast cancer cell’ markers at low levels and that therefore could be confused with DTCs. This simply reflects the power that flow cytometry has compared to IHC, where you're far more restricted in terms of the numbers of markers you can look at on each cell.
With flow cytometry, we can find combinations of markers that a normal bone marrow cell will express, but a DTC will not—and vice-versa. For example, some bone marrow cells express low levels of EpCAM, which is an epithelial cell marker and DTC marker, but bone marrow cells also express other things alongside of that, and so you can have combinatorial gating and analysis to differentiate between what's a normal bone marrow cell and what's an actual tumor cell.
How would you describe BD’s role in helping to facilitate this research?
Our collaboration with BD, along with their many insights, has been absolutely critical to our progress on this project. BD has been working with us basically every step of the way since the day we initially began working with their pre-enrichment device coupled to FACS. They’ve provided reagent support throughout all of this and a lot of intellectual involvement, as well as keying us up to various methods for doing downstream analysis of DTCs.
For instance, previously, we worked with a single-cell WTA assay from BD for looking at single-cell gene expression in smaller numbers of tumor cells. And more recently we've been working with the BD Rhapsody™ Platform, looking at gene expression in tens of thousands of cells at the single-cell level, not only in the studies with human samples that I've been talking about but also in the context of our mouse preclinical breast cancer models.
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