Case 13: AML Subtypes and FISH

FISH (specifically D-FISH) provides rapid genetic confirmation of APL (🔬: multiple Auer rods)

Benefits:

• Rapid TAT
• Ability to detect PML::RARA fusion gene even with cryptic 🤐 rearrangements (those that aren’t readily apparent on conventional karyotyping)

This next case has numerous blasts w monoblastic morphology, and I’ll give away that the genetic abnormality in this case involves chr 11 and the gene KMT2A

Challenge question 💪: what was the FISH result which initially detected the KMT2A rearrangement?

• Two 🔴, two 🟢 signals
• Two fusion 🚦 signals
• Two fusion 🚦 signals, one 🔴, one 🟢
• One fusion 🚦 signal, one 🔴, one 🟢

✨ Answer: One fusion 🚦signal, one 🔴, one 🟢 ✨

KMT2A has numerous translocation partners, so detection of a translocation involving KMT2A begins with ✨Break-apart FISH✨, not D-FISH

In AML cases w an ambiguous cytogenetics ➡️ AML FISH panel. Initial panel includes a probe which targets 11q23 (where KMT2A lives)

⚠️Important: break-apart FISH does NOT identify the translocation partner⚠️

Need to follow-up with D-FISH using a variety of different probes to common translocation partners to determine the exact genetic abnormality

Thanks for following along 🤗

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