Correct Answer: B. t(9;22)
The clinical presentation—dragging abdominal pain, massive splenomegaly, and a peripheral smear showing leukocytosis with left shift (myelocytes, metamyelocytes) plus basophilia—is pathognomonic for Chronic Myeloid Leukemia (CML). The hallmark cytogenetic abnormality in CML is the Philadelphia chromosome, which results from a reciprocal translocation between chromosomes 9 and 22: t(9;22)(q34;q11). This translocation creates the BCR-ABL1 fusion gene on the derivative chromosome 22, which encodes a constitutively active tyrosine kinase. This kinase drives uncontrolled myeloid proliferation, explaining the left-shifted leukocytosis and massive splenomegaly (extramedullary hematopoiesis). The Philadelphia chromosome is present in ~95% of CML cases and is the defining molecular feature. In India, CML accounts for 15–20% of adult leukemias, and detection of t(9;22) by cytogenetics or PCR-based BCR-ABL1 testing is mandatory for diagnosis and prognostic stratification (Sokal/Hasford score). The presence of basophilia (>2%) may indicate accelerated phase, warranting urgent tyrosine kinase inhibitor (TKI) therapy per NCCN/ESMO guidelines adopted in Indian practice.
Why the other options are wrong
A. t(8;14) — This is wrong because t(8;14) is the hallmark translocation of Burkitt lymphoma, not CML. It juxtaposes the MYC oncogene (chromosome 8) with the immunoglobulin heavy chain locus (chromosome 14), driving B-cell proliferation. Burkitt presents with lymphadenopathy and abdominal masses, not myeloid leukocytosis. NBE pairs this with 'leukocytosis' to trap students who confuse lymphoid and myeloid malignancies. C. t(8;22) — This is wrong because t(8;22) is not a recognized recurrent translocation in hematologic malignancies. This is a distractor designed to confuse students who know that chromosome 22 is involved in CML (Philadelphia chromosome) but misremember the partner chromosome. The correct partner is chromosome 9, not 8. This option exploits partial knowledge without understanding the BCR-ABL1 fusion mechanism. D. t(15;17) — This is wrong because t(15;17) is the defining translocation of Acute Promyelocytic Leukemia (APL), a subtype of AML, not CML. It creates the PML-RARA fusion gene and presents with acute leukocytosis, coagulopathy, and Auer rods—not chronic myeloid proliferation with massive splenomegaly. APL is a medical emergency requiring ATRA/arsenic, not TKI therapy. This is a classic NBE trap pairing acute vs. chronic leukemias.
High-Yield Facts
- Philadelphia chromosome t(9;22) is present in ~95% of CML cases and creates the BCR-ABL1 fusion gene encoding a constitutively active tyrosine kinase.
- CML classic triad: massive splenomegaly, left-shifted leukocytosis (myelocytes, metamyelocytes), and basophilia/eosinophilia on peripheral smear.
- BCR-ABL1 positivity (by cytogenetics, FISH, or RT-PCR) is mandatory for CML diagnosis and is the target for tyrosine kinase inhibitors (imatinib, dasatinib, nilotinib).
- Basophilia >2% in CML indicates accelerated phase and warrants urgent TKI escalation or allogeneic stem cell transplant consideration.
- Sokal score (based on age, spleen size, platelet count, and blast %) stratifies CML prognosis and guides treatment intensity in Indian practice.
Mnemonics
Philadelphia = 9;22 Ph (Philadelphia) = 9;22 — the city name has 2 syllables (9, 22). Remember: BCR on 22, ABL on 9, they fuse to make the tyrosine kinase monster. CML Triad: Spleen, Shift, Basophils S-S-B: Splenomegaly (massive), Shift (left, with myelocytes), Basophilia. If you see all three + leukocytosis, think Philadelphia chromosome.
NBE Trap
NBE pairs t(9;22) with other chromosome translocations (t(8;14) Burkitt, t(15;17) APL) to trap students who know 'chromosome 22 = CML' but confuse the partner chromosome or conflate acute vs. chronic leukemias. The presence of 'leukocytosis' without specifying 'chronic' may lure students toward acute leukemia translocations.
Clinical Pearl
In Indian practice, every newly diagnosed CML patient must undergo BCR-ABL1 testing (cytogenetics or RT-PCR) before starting TKI therapy. Imatinib 400 mg daily is the first-line DOC for chronic-phase CML; response is monitored by BCR-ABL1 transcript levels (major molecular response = MMR). Patients with t(9;22) who achieve MMR have excellent long-term survival and near-normal life expectancy.
_Reference: Robbins Ch. 13 (Hematologic Malignancies); Harrison Ch. 110 (Chronic Myeloid Leukemia)_