FRCPath Haematology Part 1 MCQs - Oncology 459

A 72-year-old man presents with a 3-month history of progressive violaceous nodular skin lesions over the scalp, face and upper chest. He reports fatigue, easy bruising and a 6-kg weight loss. Examination demonstrates multiple bruise-like plaques, mild cervical lymphadenopathy and splenomegaly (3 cm below the costal margin).

Laboratory investigations:

• Hb: 79 g/L

• WBC: 5.4 × 10⁹/L

• Platelets: 48 × 10⁹/L

• Blood film: Rare circulating medium-sized blast-like cells with irregular nuclei and fine chromatin.

• Bone marrow aspirate: 68% blasts with agranular basophilic cytoplasm.

• MPO cytochemistry: Negative.

Flow cytometry demonstrates the following phenotype: CD3-,CD34-, CD4+, MPO-, CD19-, CD123+, HLA-DR+, CD14- and CD56+.

Which ONE of the following statements is MOST CORRECT regarding this patient's disease?

A. The diagnosis is acute myeloid leukaemia with monocytic differentiation because CD4 and CD56 co-expression strongly supports monocytic lineage.

B. The neoplasm arises from mature B lymphocytes and is characterised by overproduction of immunoglobulin.

C. The tumour originates from plasmacytoid dendritic cells that physiologically produce large amounts of type I interferon in response to viral infection.

D. The diagnosis requires expression of CD34 and myeloperoxidase in addition to CD123.

E. Skin involvement is unusual, and isolated bone marrow disease is the typical initial presentation.