Translocation

Translocation — oncology-focused definition

A chromosomal translocation is a structural chromosomal abnormality in which a segment of one chromosome breaks off and attaches to another chromosome, leading to gene rearrangement or fusion.

Types:

• Reciprocal translocation: exchange of segments between two chromosomes (most common in cancer)
• Robertsonian translocation: fusion of two acrocentric chromosomes (less common in oncology)

Oncology relevance:

• Can result in:
  • Oncogene activation via placement under a strong promoter/enhancer
  • Fusion genes encoding abnormal proteins with oncogenic activity
• Often considered driver events in malignancy.

Clinical significance (for oncology pharmacists):

• Used as diagnostic and prognostic markers.
• Many translocations are directly targetable or guide therapy selection.
• Detected by karyotyping, FISH, RT-PCR, or NGS.

Classic examples:

• t(9;22) → BCR-ABL (CML, Ph+ ALL)
• t(8;14) → MYC–IgH (Burkitt lymphoma)
• t(15;17) → PML–RARA (APL; ATRA/arsenic sensitive)

Key takeaway:

Chromosomal translocations are central molecular events in many cancers, with major implications for diagnosis, prognosis, and targeted therapy.