"Masked" Ph1 chromosome in a complex three-way translocation

Area of Science:

• Cytogenetics
• Hematology
• Oncology

Background:

• Myelofibrosis is a myeloproliferative neoplasm characterized by bone marrow fibrosis.
• Cytogenetic abnormalities play a crucial role in the diagnosis and prognosis of myelofibrosis.
• The Philadelphia chromosome (Ph1) is a hallmark of chronic myeloid leukemia but can be found in other myeloid disorders.

Observation:

• A patient with myelofibrosis exhibited a complex karyotype with a "masked" Philadelphia chromosome in unstimulated peripheral blood and spleen cells.
• The masked Ph1 chromosome was part of a three-way translocation involving chromosomes 1, 11, and 22.
• Phytohemagglutinin (PHA)-stimulated cells showed a normal karyotype, suggesting an acquired abnormality.

Findings:

• The detailed karyotype revealed a complex rearrangement: 46,XX,t(1;11;22)(q24;p11;q11 or q12),t(1;22)(q24;q11 or q12).
• This complex rearrangement was predominantly observed in granulocyte-macrophage lineage cells.
• E-rosetting cells, presumed to be T lymphocytes, displayed normal karyotypes.

Implications:

• The study highlights the presence of acquired cytogenetic abnormalities, including masked translocations, in myelofibrosis.
• Understanding these complex rearrangements can refine diagnostic approaches and prognostic assessments in myeloproliferative neoplasms.
• The lineage-specific nature of the abnormality suggests distinct cellular origins or selective pressures within the bone marrow microenvironment.