Percentage of CML in which Philadelphia chromosome is positive:
**Core Concept**
The Philadelphia chromosome is a result of a reciprocal translocation between chromosomes 9 and 22, leading to the formation of the BCR-ABL fusion gene. This genetic abnormality is a hallmark of Chronic Myeloid Leukemia (CML) and is responsible for the proliferation of malignant cells.
**Why the Correct Answer is Right**
The Philadelphia chromosome is present in more than 90% of CML cases, making it a diagnostic and prognostic indicator of the disease. The BCR-ABL fusion gene, resulting from this chromosomal translocation, activates tyrosine kinase activity, leading to uncontrolled cell proliferation and resistance to apoptosis. This specific genetic abnormality is a crucial factor in the pathogenesis of CML.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately represent the percentage of CML cases with the Philadelphia chromosome.
**Option B:** This option is also incorrect, as it does not reflect the correct percentage of CML cases with the Philadelphia chromosome.
**Option D:** This option is incorrect, as it does not accurately represent the percentage of CML cases with the Philadelphia chromosome.
**Clinical Pearl / High-Yield Fact**
The presence of the Philadelphia chromosome is a key diagnostic feature of CML, and its detection is essential for guiding treatment decisions. The development of tyrosine kinase inhibitors (TKIs) has significantly improved the prognosis of CML patients, making early diagnosis and detection of the Philadelphia chromosome crucial.
**Correct Answer:** C. 95%