A 62-year-old man reports early satiety, fatigue, and generally feeling unwell. On examination he has a large spleen, appears pale, and the rest of the examination is normal. His blood count is abnormal; the WBC is 50,000/mL with increased mature granulocytes, hemoglobin 9.5 g/dL, and platelets 450,000/mL. Which of the following cytogenetic changes is most characteristic of his condition?
High-Yield Explanation
This is a case of chronic myelogenous leukemia. The reciprocal translocation involves the long arms of 22 and 9, and results in translocation of the ABL proto-oncogene from chromosome 9 adjacent to a portion of the BCR gene on chromosome 22. The resultant abnormal chromosome 22 is known as the Philadelphia (Phi) chromosome.