Atypical myeloproliferative neoplasm with concurrent BCR-ABL1 fusion and CALR mutation: A case report and literature review.

Rationale: Concurrent calreticulin (CALR) mutation and BCR-ABL1 fusion are extremely rare in chronic myelogenous leukemia; to date, only 12 cases have been reported.

Patient Concerns: A 57-year-old male who had an 11-year history of essential thrombocytosis presented to our hospital with leukocytosis and marked splenomegaly for 3 months.

Diagnoses: Chronic myelogenous leukemia with myeloid fibrosis arising on the background of essential thrombocytosis harboring both BCR-ABL1 fusion and type-1 like CALR mutation.

Interventions: Imatinib was started at 300 mg daily and increased to 400 mg daily after 3 months; interferon was added after 12 months.

Outcomes: Partial cytogenetic response was achieved after 3 months of imatinib therapy and complete cytogenetic response was achieved after 1 year of treatment. However, CALR mutation was still present with a stable mutational allele burden.

Lessons: In this case report and review of additional 12 cases with simultaneous presence of CALR-mutation and BCR-ABL1 fusion, we highlighted the importance of integrating clinical, morphological, and molecular genetic data for classifying atypical myeloid neoplasms.