Researchers from China presented the rare case of a patient with aggressive systemic mastocytosis with intestinal tract involvement whose disease was mimicking a blastic plasmacytoid dendritic cell neoplasm.

The 44-year-old male patient had experienced abdominal discomfort for 4 years and diarrhea for 5 months. The researchers identified a protuberant lesion in his cecum with adjacent lymphadenopathy. The lesion had diffuse infiltration of medium-sized round/oval cells in the lamina propria and expressed CD45, CD117, CD25, CD123, CD56, CD4, CD35, CD68, and CD163, mimicking a blastic plasmacytoid dendritic cell neoplasm.

Upon genetic testing, the researchers identified a missense mutation in the KIT gene (D816V). The patient’s serum tryptase level was 38.56 ng/mL.

Systemic mastocytosis “should be considered in patients with long-term diarrhea symptoms and hematopoietic/lymphoid-appearing tumors,” the researchers, led by Yingyong Hou, concluded. 

The patient was treated with 200 mg of avapritinib once a day, which dramatically improved his condition. 

Read more about the treatment of systemic mastocytosis

However, 1 month later, he started to develop memory impairment. The dose of the treatment was reduced to 75 mg once a day, and his disease did not recur in the 1-year follow-up. 

“The rare side-effect of memory impairment in this case helps to accumulate the experience of avapritinib in treating KIT D816V-mutant [systemic mastocytosis],” the researchers wrote.

The case report is under review for publication in Diagnostic Pathology.

Systemic mastocytosis is a rare disease characterized by the infiltration of mast cells into tissues other than the skin. The disease can be indolent, smoldering, associated with a hematologic neoplasm, aggressive, or classified as mast cell leukemia.

Avapritinib, sold under the brand name Ayvakit™, is a selective small molecule kinase inhibitor that specifically targets activation-loop mutants of KIT, including KIT D816V. It is approved by the US Food and Drug Administration (FDA) to treat advanced systemic mastocytosis.


Zhang X, Han J, Ji Y, Hou Y. Systemic mastocytosis mimicking blastic plasmacytoid dendritic cell neoplasm: a case report. Research Square. Preprint posted online August 29, 2022. doi:10.21203/