Mastocytosis

Question 1

Systemic mastocytosis surface markers

Answer 1

CD2+CD25 mast cells
(Subset CD30+)

Question 2

Systemic mastocystosis

Answer 2

KIT 816V

Question 3

How does Mastocytosis in Adults and Children differ?

Answer 3

Adults:
* KIT D816V mut
* Peristent and multiorgan involvement

Kids:
* 30% D816F mut and 40% exon 8-11
* Skin
* Spont improvement at puberty

Question 4

WHO 2022 Classicfication of Mastocytosis

Answer 4

1. Cutaneous
2. Systemic
3. Localised (Mast cell tumour)

Question 5

Diagnostic criteria for Cutaneous Mastocytosis and 3 forms

Answer 5

Dx
1. Skin lesions with biopsy
2. No systemic involvement

3 Forms:
1. Maculopapular CM (Mono and Polymorphic)
2. Diffuse CM
3. Mastocytoma

Question 6

Definition of Systemic Mastocytosis

Answer 6

• Clonal neoplastic proliferation
• Of Morph and IMPT abN mast cells
• Accumulation in 1+ organs
• ± skin involvement

Question 7

Morphologic and IMPT Fts of AbN Mast Cells

Answer 7

Morphologic:
1. Multifocal clusters (>15)
2. Spindle shaped
3. Hypogranular/uneven distribution
4. Atypical Nuclei
5. Monocytoid

IMPT:
1. Normal: Positive CD117 and Tryptase
2. Aberrant: CD25, CD2 (some), CD30(subset)

Question 8

Diagnostic criteria for Systemic Mastocytosis

Answer 8

1 Major + 1 Minor OR 3+ minor

Major:
1. Multifocal dense infiltrate

Minor:
1. 25%+ MCs are aMCs
2. KIT D816V mutation
3. AbN immunophenotype
4. Baseline sTryptase >20ng/mL

Question 9

Staging of Systemic Mastocytosis

Answer 9

B criteria (Burden)
1. MCs in BM, >30% on Histo
2. sTryptase >200 or KIT D816V VAF >10
3. Signs of MDS, MPN and eosinophilia
4. Organ involvement (NOT DysFX)

C criteria (Organ dysFx)
1. BM with cytopenias
2. Liver with Liver impairment
3. Skeletal with osteolytic lesions
4. Spleen with hypersplenism

I. Non advance (B):
1. Indolent (1 B) Tryptase low and KIT VAF low
2. Smouldering (2+B) Tryptase low and KIT VAF high

II. Advance (C): Tryptase high and KIT VAF low
1. Aggressive (C)
2. MC Leukaemia (>20% MCs in BM)
3. Associated with Haem Neoplasms Tryptase high and KIT VAF high

III. NEW: Well differentiated SM (WDSM)
* Kids > Persists to adulthood
* Round well granulated MCs
* NOT CD2/CD25 positive BUT CD30 positive
* Non-KIT D816V mutations
* Tx with Imatinib

Question 10

Treatment of SM

Answer 10

Non-advanced:
* Sx Tx (Histamine)

Advanced:
* Multiagnet chemo (Cladrabine, INFa ± C/S)
* AlloHSCT
* New: Midostaurin