REFRACTORY Blastic Extramedullary Plasmacytoma

Abstract 5102

Tumour classification defines clinically distinctive, non-overlapping disease entities that serve the basis for future investigation and therapeutic management. The World Health Organization committee for classification of haematological malignancies is truly one of the first worldwide group to provide a consensus approach encompassing morphology, immunophenotyping, genetic and clinical features. However, there are limitations. Not all diseases fit into specific categories. Attention to unique clinical presentations facilitates our continued education. We report a blastic variant of an extramedullary plasmacytoma.

A fit 61 year old Caucasian man presented with a progressive neck and right upper limb (RUL) pain. No other relevant past medical or family history. Examination revealed a sensory neuropathy involving the 7^th cervical dermatome. MRI cervical spine revealed a 5cm right paravertebral mass extending from C5-T1, surrounding the right vertebral artery and the roots and trunks of the right brachial plexus. It extended into the right neural foramina at the C5-C6, C6-C7 and C7-T1 levels with more minimal invasion at the C4-C5 level. Over a two week period he complained of increasing RUL pain, a right Horner's syndrome and weakness of the small muscles of his hand. An excision biopsy of the mass was performed and staging investigations were completed including CT body, lumbar puncture, bone marrow aspirate/biopsy, serum and urine protein electrophoresis. A PET/CT showed the right sided paraspinal nodal mass with low to moderate metabolic activity.

A diffuse, monotonous population of medium size cells with average nuclear: cytoplasm ratios, blastic chromatin, round nuclei and smooth contours surrounding a relatively unremarkable reactive lymph node. Mitoses are readily apparent, along with 'starry sky' appearance imparted by numerous tangible-body macrophages within the infiltrate. An extensive immunohistochemical panel were performed. The cells of interest express CD45, Cd38, vs38, CD138, MUM1, CD4, CD15, p53, weak CD19 and lambda light chain. The proliferation rate by Ki-67 is high approximately 60%. The overall phenotype was consistent with plasma cell differentiation but the mitotic rate and morphological rate does not fit well.

An initial response to definitive radiotherapy (40Gy/20fr) was swiftly followed 6 weeks later with a profound C5 radiculopathy. MRI imaging confirmed an extra-axial lesion, lying partially within the radiation port. The patient is now receiving salvage chemotherapy.

The behaviour of this lesion both under the microscope at the bench and the bedside is at odds with that predicated for a plasmacytoma, highlighting the critical importance of interplay between different medical disciplines. While blastic variants have been described for many haematological malignancies, it has not been previously reported in this situation.