How is BPDCN diagnosed?
So for this rare entity BPDCN, we had to actually convene a group of folks together. And we've had several guidelines published to be able to understand how to diagnose this disease. I would say that BPDCN, unlike my other leukemias for the most part, traditionally almost always affects compartments outside of the blood and bone marrow. So usually AML myeloid leukemia usually is restricted to the blood and bone marrow every once in a while can pop up as an extramedullary or outside the bone marrow. But BPDCN has a predilection for that.
And so because of that, we have four major compartments that BPDCN can affect. And that's how diagnosis can be made. One is the skin. That's one of the most unusual parts of BPDCN is that almost all patients at some point may have skin involvement. The skin lesions are distinct, usually purple violations, dark colored lesions. Of course, you have to biopsy to make sure it's BPDCN, and not AML, leukemia cutis, infection, benign conditions, etc.. So number one for the diagnosis. If there's an abnormal skin lesion biopsy taking a picture characterizing it.
Number two BPDCN does affect the bone marrow blood like most other leukemia subtypes. And so a bone marrow biopsy with cytogenetics flow cytometry immunohistochemistry is essential in all patients. And usually there we have certain markers that delineate BPDCN from other more common leukemias. And that's usually the triad of CD4, 56, 123 positive along with TCL1, TCF4, and even CD303. So that's one and two skin biopsy and bone marrow biopsy.
But three and four are very important, I would say essential in the staging of all BPDCN particularly at baseline. Number three is that it can affect the lymph nodes at a decent frequency. And so imaging of the body as one would do in lymphomas. So a PET CT or CT scan at baseline. And finally that's a very important point. We've seen for many reasons apparently likes to go unfortunately for us to the central nervous system. And so a lumbar puncture or a spinal tap is essential for all patients at baseline, not only to sample the fluid, but also we give a squirt of intrathical or in the spinal fluid chemotherapy. And I recommend approximately eight of those throughout the course of the BPDCN treatment.
And so just to summarize, because BPDCN is a protean manifestation entity affect almost all parts of the body or major compartments, which results in the staging and the identification. So skin, bone marrow, lymph node and CSF identification. One could probably estimate that there's probably 500 cases a year in the US. So it's really quite rare. And it's probably less than that actually. It's really a diagnosis that's become more clear over time. I'll point that out.
You know, there are WHO diagnostic criteria. And it's really essential that a pathologist and pathologist today are more aware of this entity and more prone to look for, because there are certain expression profiles on cells that tell us BPDCN, or there are staining of cells that can tell us BPDCN, dermatologists because sometimes skin manifestations or initial findings are more likely think to recognize and dramatic pathologists that there may be BPDCN and refer patients appropriately to centers.
And that's the other key part. Referral key centers where they have volume and be able to see this disease and know how to treat it. So ultra rare disease not very frequent, not very common in the community setting, almost always treated in a tertiary academic center, particularly centers that have excellence and interest in understanding and treating these diseases.
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