Case Study Highlights Importance of Next-Generation Sequencing in Patients With ET

Authors of a case study suggest screening for additional mutations using next-generation sequencing (NGS) should be considered in patients with essential thrombocythemia (ET), particularly as the disease progresses.

Findings were published in the journal Platelets. Although ET is a rare disease, cases have been reported where patients have the condition with MPL and Type 1 calreticulin (CALR) gene mutations. In the current case study, researchers report the first patient to their knowledge with ET and both MPLS204P and Type 2 CALR mutations.

The disease progressed to an accelerated phase 3.5 months following diagnosis. In addition, “CALR mutation disappeared and new mutations emerged as the disease progressed, such as ASXL1, CBL, ETV6, and PTPN11 mutation,” the authors wrote.

ET is a classic myeloproliferative neoplasm (MPN). Previous studies have found mutations in JAK2, CALR and MPL are collectively detectable in 83 % of patients with ET. “However, JAK2, CALR, and MPL are found to be mutated in a mutually exclusive fashion, suggesting that they drive transformation through the same pathway,” the authors explained.

One study found that of 685 patients with CALR-mutated MPNs, just 0.3% had concurrent MPL mutations.

By assessing a patient with ET and combined MPL S204P and Type 2 CALR mutations, the researchers assessed the contributions of genetic factors to disease pathogenesis.

The patient was a 67-year-old woman from China. She was admitted to the People’s First Hospital in November 2019 with new onset thrombocytosis (platelets 1097 × 10⁹/L). She had no hepatosplenomegaly, no history of reactive thrombocytosis, or other cardiovascular risk factors like hypertension, diabetes, or cigarette smoking.

There was also no evidence of reactive thrombocytosis. NGS showed the presence of CALR (K385Nfs × 47; variant frequency [VF] = 27.8%), MPL (S204P; VF = 71.5%) and SETBP1 (W222S; VF = 50.2%) mutations.

Based on the International Prognostic Score for Thrombosis in ET, she was rated as “low risk.” However, according to mutation-enhanced international prognostic systems in ET, she was classified as “intermediate risk.”

Following a diagnosis, the patient was treated with hydroxyurea 500 mg twice daily and aspirin 100 mg once daily. Additional NGS was carried out after 3.5 months of treatment.

“Results revealed the persistence of the MPL (S204P; VF = 94.7%) and SETBP1 (W222S; VF = 47.4%) mutations, the disappearance of the CALR (K385Nfs × 47) mutation, and the acquisition of mutations in ASXL1 (E635Rfs × 15; VF = 27.9%), RUNX1 (D198 G; VF = 37.5%), CBL (c.1227 + 2T>C; VF = 53.2%), ETV6 (P214 L, VF = 7.5%), and PTPN11 (S502P; VF = 7.2%),” the authors wrote.

In March 2020, she was treated with decitabine in combination with cytarabine, aclarubicin hydrochloride, and granulocyte colony-stimulating factor (DCAG). She then refused further treatment for financial reasons and developed a blood transfusion dependence in 2021.

Following another DCAG regimen in July and September and a decision by the patient’s family to abandon treatment, the patient passed in December 2021.

“The disappearance of the CALR mutation and an increase in the MPL mutant burden were observed in this ET patient during follow-up, suggesting the biclonality of the CALR and MPL mutations. The disappearance of the CALR mutation is highly likely to be due to the clonal competition and the expansion of the MPL mutations,” the researchers said. “Cells with a MPL mutation would achieve clonal dominance much faster than those with a CALR mutation.”

Results of the case study also suggest that additional mutations beyond JAK2, CALR, and MPL are compatible with disease progression.

The researchers’ molecular approach cannot detect mutations in noncoding sequences and gene fusions or even mutations at low variant frequency, marking a limitation on their findings. They also note it is unclear whether acquired mutations in other genes contribute to disease progression, as they only performed targeted sequencing of 29 genes.

Reference

Wang J, Fu W, Bao W, et al. Genomics of clonal evolution in a rare essential thrombocythemia with coexisting type 2CALR and MPL S204P mutations. Platelets. Published online February 14, 2023. doi:10.1080/09537104.2023.2176167