Desai and Participants Differentiate BPDCN From Other Diagnoses

Pinkal Desai, MD, MPH (Moderator)

Associate Professor of Medicine

Charles, Lillian, and Betty Neuwirth Clinical Scholar in Oncology

Weill Cornell Medical College

New York, NY

DISCUSSION QUESTIONS

• What are your initial impressions of this patient?
• What should be included in the differential diagnosis?
• What diagnostic assessments would you perform/order?

PINKAL DESAI, MD, MPH: If this patient came to your practice, what would be your initial impressions of this case? Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is in the differential diagnosis, but what would be the other things you would see? We tend to see it once a diagnosis is made many times from referrals, but how would you think of this?

ILYA BLOKH, MD: If we see somebody with constitutional symptoms, blasts, and some skin lesions, we could always pursue a skin lesion but with the blasts, I would also do a peripheral blood flow [cytometry test] and a bone marrow biopsy.

DESAI: Do you usually just do the flow [cytometry] and wait for the results? Or would you go straight to a bone marrow biopsy in this case?

BLOKH: In private practice, I have interventional radiology do the bone marrow biopsy, since I don't have time to do them. By the time I set it up, it's never going to be done the same day, so I just send off the peripheral blood [test] to get that started. Then they may get some answers within a day or 2, and then I set up the patient with a bone marrow biopsy as an outpatient [option] through interventional radiology.

DESAI: Would you usually biopsy the skin? Or is that something you wait on to get the results from the flow cytometry?

BLOKH: Because it's superficial lesions, it's very tempting to do a skin biopsy. Maybe that could even give me an answer just as quick as the peripheral blood flow cytometry. I would consider getting a skin biopsy because purplish lesions look very suspicious in general for some kind of oncologic process going on.

DESAI: Interestingly, I just had a BPDCN case with only skin nodules. That's where the blood counts were completely normal, and the patient just presented with these nodules. They were not even that extensive; there were 2 or 3 on the legs. We were a little surprised at the diagnosis. We chose to biopsy the skin, and the diagnosis was BPDCN, but they had absolutely normal complete blood count and no bone marrow involvement. In this case, with circulating blasts, it's very easy to send it by flow cytometry and they may not need a biopsy of the skin if you get an easy diagnosis from blood flow. But just keep in mind that sometimes you can have an isolated skin-only BPDCN [diagnosis]. It's very rare. I've seen it once in my entire career.

CASE UPDATE

• Bone marrow biopsy: 40% blasts by morphology; 80% cellular marrow with interstitial infiltrate
• Immunohistochemistry of neoplastic cells: CD123, CD4, CD56, TCL1 positive
• Flow cytometry:
  • CD4, CD56, CD123 positive
  • CD34 and T- and B-cell lineage-specific markers negative
• Cytogenetics: 46 XY
• Lumbar puncture did not indicate central nervous (CNS) involvement
• The patient was ultimately diagnosed with BPDCN based on clinical and histopathological findings.

DESAI: This is relevant because there is a high chance of CNS involvement in patients with BPDCN. It goes with this extramedullary [aspect] to the disease; it can involve skin, organs, liver, and CNS so generally, if you have a diagnosis, lumbar puncture is important. And while you're doing the lumbar puncture, you want to treat it while you're there so that you don't have to go back in again, maybe with methotrexate or rituximab [Rituxan]/cytarabine intrathecally.

If somebody presents with these skin nodules and no bone marrow involvement, it's possible that they will only see a dermatologist and not the hematologist/oncologist. Have you seen the skin-only involvement with any other malignancies? Is this a common sort of referral from dermatology or primary care physician to you?

MOHAN PREET, MD: I have an 80-year-old man with Kaposi sarcoma, but he has HIV negative Kaposi sarcoma. With this new information, maybe we need to have a second look at his biopsy.

DESAI: I think many of the cutaneous lymphomas or cutaneous T-cell lymphomas, and natural killer cell lymphomas—they may be in the category where they have BPDCN and it's a skin-only manifestation. Many times, cutaneous T-cell lymphomas are handled by a dermatologic oncologist and aren't seen by a hematologist.

MARC BRAUNSTEIN, MD: Other things I might see in this case would be cutaneous mastocytosis or even cutaneous amyloidosis might appear.

DESAI: Certainly mastocytosis, another rare disorder can mimic this, and mastocytosis is a great mimicker. Just like BPDCN, it can involve constitutional symptoms, hepatosplenomegaly, similar findings. Tryptase is a telling sign for mastocytosis, if you see some somebody like that. It can have bone marrow involvement, so you can have cytopenias with mastocytosis. That's a great point. Tryptase would be one of the things we would [test for] to make sure that it's not mastocytosis.