Splenic mass in a case of CALR-mutated essential thrombocythemia.

We report here an intrasplenic large mass in an elderly case of essential thrombocythemia (ET)-myelofibrosis. Laparoscopic splenectomy revealed extramedullary hematopoiesis (EMH) and a type 1 CALR gene mutation (CALR-c.1092_1143del52) in the splenic mass. It remains to be determined if CALR-mutated ET has an increased tendency to develop mass-forming EMH.

An 86‐year‐old Japanese female had splenomegaly with a history of elevated platelet counts (>500 000/µL) for more than 10 years. Laboratory tests showed a WBC of 30 600/µL and a platelet count of 1 031 000/µL, in association with high serum soluble IL2‐receptor (1001 U/mL), low serum IgG (712 mg/dL), and low complement CH50 levels (5 U/mL). Essential thrombocythemia (ET)1 was suspected, but JAK2 V617F gene mutation was negative. An abdominal CT revealed a huge mass within the spleen (Figure 1A). Bone marrow revealed myelofibrosis grade 1‐2 (Figure 1B). Laparoscopic splenectomy showed that the central round tumorous part of the spleen, which measured 6.2 cm × 6.3 cm, was clearly differentiated from the non‐tumorous part on the cut surface (Figure 1C). Histopathology revealed trilineage extramedullary hematopoiesis (EMH), but with particularly increased numbers of megakaryocytes with nuclear atypia in the tumorous part (Figure 1D). In the splenic mass, we found a type 1 CALR gene mutation (CALR‐c.1092_1143del52), which is a major abnormal type of CALR. Eventually, the patient was diagnosed as having a splenic mass of EMH, as consequence of CALR‐mutated ET. This case was unexpected and uncharacteristic because the spleen is not among the organs involved with mass‐forming EMH.2

Figure 1

A, Computed tomography (CT) scan of the abdomen showing the splenic mass. B, Bone marrow biopsy revealing myelofibrosis grade 1‐2 (silver impregnation stain; original magnification ×400). C, Gross appearance and the cut surface of the resected spleen showing clear delineation between the tumorous and non‐tumorous parts. D, Histopathology of the tumorous part of the spleen showing markedly increased numbers of megakaryocytes with nuclear atypia (HE stain; original magnification ×400)

CONFLICT OF INTEREST

The authors have no conflict of interests to declare.

AUTHOR CONTRIBUTION

SI and SK: treated the patient, SI: engaged in molecular diagnosis and wrote the manuscript, SK: performed bone marrow biopsy, JH: performed laparoscopic splenectomy, KN: performed hispathological diagnosis. All authors read and confirmed the final version of manuscript.