A 40‐year‐old man was referred on account of a persisting thrombocytosis. He was a smoker but gave no other past medical history of note and physical examination was unremarkable. The full blood count showed Hb 144 g/l, WBC 6.7 × 109/l, neutrophils 3.5 × 109/l and platelets 621 × 109/l. Serum ferritin was 120 μg/l. He had normal serum biochemistry and the ESR and CRP were normal. The blood film showed mild platelet anisocytosis but no other abnormality. The working diagnosis was essential thrombocythaemia (ET) but mutations in JAK2 and MPL genes and deletions in CALR gene were not identified. The bone marrow trephine biopsy sections were mildly hypercellular (60%) and showed increased numbers of megakaryocytes forming clusters (left images, H&E, centre images, immunoperoxidase for CD42b) (all images ×50 objective). The megakaryocyte morphology was largely normal but some larger forms were recognised (lower centre image). There was some mild focal increase in reticulin staining (grade 1 of 3, right images). Erythroid and myeloid activity were normal and no abnormal infiltrate was noted. A diagnosis of ET was made.
Essential thrombocythaemia is a myeloproliferative neoplasm characterised by persistent thrombocytosis in the absence of anaemia or polycythaemia. Around 85% of cases will show abnormalities in JAK2, CALR or MPL but so called ‘triple‐negative’ cases do exist (Cazzola and Kralovics 2014). In such circumstances the diagnosis is one of exclusion when persistence of thrombocytosis is shown, reactive causes are excluded and the bone marrow morphology supports the diagnosis and excludes other myeloproliferative neoplasms (polycythaemia vera, primary myelofibrosis and chronic myeloid leukaemia). Bone marrow trephine biopsy sections typically show only mild hypercellularity, an increase in medium to large megakaryocytes with focal aggregations or ‘clustering’ with only a minimal, if any, increase in reticulin staining. A cluster requires three or more megakaryocytes to be adjacent to, or touching, each other. Cases that are suspicious for ET, but without sufficient features for a definitive diagnosis, are not uncommon. A proportion of these triple‐negative cases show either a low allele burden, an alternative mutation site in JAK2 or MPL or a mutation only identified by examining platelet RNA (Angona et al. 2016), but evidence of clonality is currently not demonstrable in all cases that appear to be true ET.
References
1 Angona A, Fernández‐Rodríguez C, Alvarez‐Larrán A, Camacho L, Longarón R, Torres E et al. (2016) Molecular characterisation of triple negative essential thrombocythaemia patients by platelet analysis and targeted sequencing. Blood Cancer J, 6, e463.
2 Cazzola M and Kralovics R (2014) From Janus kinase 2 to calreticulin: the clinically relevant genomic landscape of myeloproliferative neoplasms. Blood, 123, 3714–3719.
MCQ
1 Essential thrombocythaemia:Causes itch in a minority of patientsIs associated with JAK2 V617F in more than half of patientsIs most often an incidental diagnosis in an asymptomatic patientIs Ph+, BCR‐ABL1+ in only a minority of patientsTypically has small plateletsFor answers and discussion, see page 206.
20 Hairy cell leukaemia
A 43‐year‐old man presented with fatigue and early satiety. His automated full blood count showed Hb 75 g/l, WBC 15.3 × 109/l, lymphocytes 3.62 × 109/l, neutrophils 0.6 × 109/l, monocytes 11.1 × 109/l and platelets 32 × 109/l. He had an easily palpable spleen without lymphadenopathy. The blood film showed plentiful hairy cells with a typical round or ovoid nucleus, absent nucleoli and pale blue fluffy irregular cytoplasm (top images ×100 objective): some cells showed an indented peanut‐shaped nucleus (top right). The marrow trephine biopsy sections (×50) showed a diffuse infiltrate of lymphoid cells with voluminous cytoplasm (bottom left, H&E), generating grade 1–2/3 fibrosis (bottom centre, reticulin stain) with strong uniform CD20 positivity (bottom right, immunoperoxidase). Flow cytometric studies on the peripheral blood lymphoid cells indicated a CD19+, CD20+, CD79b+, CD22+, FMC7+, HLA‐DR+, CD10+, CD11c+, CD25+, CD103+, CD123+ and lambda‐restricted immunophenotype. The diagnosis is hairy cell leukaemia (HCL), a rare mature B‐cell neoplasm typically causing splenomegaly and cytopenias, most notably neutropenia and monocytopenia (note that the automated analyser has miscounted the hairy cells as monocytes). The disease typically infiltrates the bone marrow in a diffuse pattern with associated fibrosis. Bone marrow aspirates are typically ‘dry’ so a careful assessment of the blood film is frequently useful in anticipating this condition.
The images on the facing page are of peripheral blood from a patient with splenic marginal zone lymphoma (SMZL). There are some morphological similarities to HCL but the cells here are a little smaller and have less voluminous cytoplasm showing fronds and tufts (×100). The cytoplasmic border is somewhat easier to define. The cells here showed a mature pan‐B phenotype with CD11c positivity whilst CD25, CD103 and CD123 were not expressed.
The pattern of bone marrow infiltration also differs in SMZL. This condition can show a degree of interstitial infiltration but it more typically demonstrates focal nodular, paratrabecular and intrasinusoidal disease.
Hairy cell leukaemia variant, in which the neoplastic cells have prominent nucleoli, must also be distinguished from HCL. Despite the name, this condition has no close relationship to hairy cell leukaemia.
MCQ
1 Hairy cell leukaemia:Can be distinguished from chronic lymphocytic leukaemia on the basis of CD200 expressionIs associated with a BRAF V600E mutation in the majority of patientsIs best distinguished from hairy cell leukaemia variant by expression of CD25, CD123 and CD200Requires assessment of tartrate‐resistant acid phosphatase (TRAP) activity for a firm diagnosisUsually has collagen fibrosisFor answers and discussion, see page 206.
21 Mantle cell lymphoma in leukaemic phase
A 66‐year‐old man presented with dizziness, headaches and difficulty walking. On assessment he was globally confused but had no specific neurological deficit. His full blood count showed Hb 79 g/l, WBC 602 × 109/l and platelets 70 × 109/l. He had splenomegaly but no significant lymphadenopathy. His blood film showed pleomorphic lymphoid cells varying in size from small to large, with condensed nuclear chromatin and prominent nuclear clefts and convolutions, with many of the larger cells showing cytoplasmic vacuoles (all images ×100 objective). Immunophenotyping studies identified a mature CD5−, kappa‐restricted, B‐cell lymphoproliferative disorder expressing CD19, CD20, CD79b, FMC7 and CD38. Immunohistochemistry on the marrow trephine biopsy sections showed the cells to express nuclear cyclin D1 and on karyotypic analysis a t(11;14)(q13;q32) translocation was identified with, in addition, loss of the short arm of chromosome 17 in 60% of cells. The features here are most consistent with leukaemic non‐nodal mantle cell lymphoma.
In view of the presentation, in keeping with cerebral leucostasis, he was treated by leucapheresis and emergency chemotherapy incorporating high‐dose corticosteroids, cyclophosphamide and vincristine. This was followed by six courses of high‐dose cytarabine and rituximab with an incomplete clinical response with persisting splenomegaly on CT imaging. The splenic anatomy remained abnormal with focal hypodense lesions and a splenectomy was performed. This showed extramedullary haemopoiesis but no evidence of residual lymphoma. This patient remains well and in remission 12 years later.
Mantle cell lymphoma constitutes between 3 and 10% of non‐Hodgkin lymphomas. Typically, it involves lymph nodes, but the spleen and bone