The most striking and unique feature of BPDCN is its involvement of the skin. At least 80% of patients have skin involvement at the time of initial diagnosis. The skin lesions can be single, or wide spread and numerous; they can be nodular and indurated or can be patchy erythema that mimics inflammatory or allergic conditions. However, the most common skin presentation is one or more violaceous, bruise-like plaques or tumors that can be found in any region of the body. The disease usually begins with a single lesion, which often then spreads to contiguous areas or more distantly in the skin. Interestingly, up to 50% of patients will not have concurrent bone marrow involvement (so-called “skin-only” disease). In those with bone marrow disease, only a minority will have circulating peripheral blood BPDCN cells. Anemia or thrombocytopenia are signs that the bone marrow may be involved. Lymph node and/or splenic involvement is present in approximately 40%. BPDCN has an increased propensity to involve other visceral sites such as the lung, breast, oral cavity, and other mucosa such as the cervix. In our experience, extramedullary involvement by BPDCN is more frequent than in AML, including compared to AMLs with monocytic differentiation (FAB M4 and M5), which can involve mucosal surfaces, gingiva, and other organs including the central nervous system.
We recommend that the initial evaluation for a patient with suspected BPDCN includes a full body skin exam, preferably by a dermatologist or oncologist with experience in skin malignancies, with skin biopsy of suspicious lesions; a bone marrow aspiration and biopsy; and full body imaging with either contrast-enhanced CT scan or positron emission tomography (PET)-CT scan.
Central nervous system (CNS) involvement by BPDCN is more frequent than in AML or other myeloid neoplasms such as MDS and CMML. Occult CNS involvement at diagnosis may be as high as 30%, and symptomatic CNS disease is often a feature of relapsed or refractory disease. Therefore, we recommend lumbar puncture for cytology and flow cytometry, plus prophylactic intrathecal chemo therapy for all patients at diagnosis, and for all patients with neurologic symptoms or signs at any time in their disease course. For patients with no CNS involvement at diagnosis, we recommend a full course of prophylactic intrathecal chemotherapy, concurrent with systemic therapy, following a regimen similar to that used for high risk acute lymphoblastic leukemia.
