Acute Leukemias (ALL & AML) and Myelodysplastic Syndromes

Comprehensive vocabulary flashcards covering basic definitions, classification systems (FAB vs. WHO), cytogenetics, and cytochemical staining patterns for Acute Lymphoblastic Leukemia, Acute Myeloid Leukemia, and Myelodysplastic Syndromes.

Acute Lymphoblastic Leukemia (ALL)

A fast-growing blood cancer characterized by blasts arrested in lymphoid differentiation, with $>20\%$ blasts in the bone marrow or peripheral blood according to WHO criteria.

WHO Blast Cutoff

$\ge20\%$ blasts in the bone marrow or peripheral blood for the diagnosis of acute leukemia.

Aleukemic ALL

An uncommon presentation of Acute Lymphoblastic Leukemia where no blasts are found in the peripheral blood.

Rieder's deformity

A nuclear cleft or indentation often seen in L1 and L2 ALL when hyperchromatin is present.

Hand-mirror deformity (HMD)

A characteristic cytoplasmic tail that is an immunological hallmark of the L2 classification when present in high percentages.

FAB L1 Classification

The most common form ($75\%$) in children, featuring small uniform microblasts with scanty cytoplasm and inconspicuous nucleoli.

FAB L2 Classification

Found in $20\%$ of cases (often adults or children $<2$ years), featuring large, heterogeneous cells with variable cytoplasm and distinct, sharp nucleoli.

FAB L3 (Burkitt type)

A rare ($5\%$) form featuring large, homogeneous cells with intensely basophilic cytoplasm and prominent vacuoles; it is identical to Burkitt lymphoma cells.

CALLA (CD10)

A key marker of Common ALL ($70\%$ of cases); its presence indicates the most favorable B-lineage prognosis where cure is possible with chemo alone.

T-ALL

Comprising $15\%$ of cases, it typically affects males ($5:1$ ratio), presents with a mediastinal mass and high WBC, and is positive for $CD3$, $CD5$, and $CD7$.

t(12;21) (TEL-AML1)

A structural translocation in precursor B-ALL that cannot be detected by regular cytogenetics; it is the only translocation associated with a GOOD prognosis.

t(9;22) (BCR-ABL1)

The Philadelphia chromosome; associated with a POOR prognosis in ALL (unlike CML) and often seen in older patients with L2 morphology.

Minimal Residual Disease (MRD)

Leukemic cells detectable by PCR even when the patient is in clinical remission; presence of any MRD indicates a high risk of relapse.

FAB Blast Cutoff for AML

$\ge30\%$ blasts of the non-erythroid cells (NEC) in the bone marrow.

AML minimally differentiated (M0)

Undifferentiated, non-granular blasts where $MPO < 3\%$ by light microscopy; requires electron microscopy or anti-MPO antibodies for diagnosis.

AML without maturation (M1)

Myeloblasts make up $\ge90\%$ of NEC with rare Auer rods; $MPO$ and $SBB$ must be $>3\%$ for diagnosis.

AML with maturation (M2)

Features $30\text{--}89\%$ myeloblasts with maturing granulocytes; often associated with $t(8;21)$ and a favorable prognosis.

Acute Promyelocytic Leukemia (M3 / APL)

Characterized by $\ge50\%$ promyelocytes, a high risk of DIC, and the unique $t(15;17)$ translocation; treated with ATRA and ATO.

Faggot cells

Cells containing stacked Auer rods found in both the hypergranular and hypogranular variants of AML M3.

Acute Myelomonocytic Leukemia (M4)

Features a dual population of myeloblasts and monocytoid cells; the M4eo subtype with $inv(16)$ has an excellent prognosis.

Acute Monocytic Leukemia (M5)

Consists of $\ge80\%$ monocytic cells ($M5a$ is mostly monoblasts; $M5b$ is mostly promonocytes); often infiltrates gums and CNS.

Acute Erythroleukemia (M6)

A compound leukemia where $\ge50\%$ of all nucleated bone marrow cells are erythroid and $\ge30\%$ of NEC are myeloblasts.

Acute Megakaryoblastic Leukemia (M7)

The most common AML in Down syndrome; characterized by polymorphic blasts with cytoplasmic blebs and bone marrow myelofibrosis (dry tap).

Myeloperoxidase (MPO)

The most important cytochemical stain for distinguishing AML (positive) from ALL (always negative); uses a $3\%$ cutoff.

Sudan Black B (SBB)

A stain for neutral fats and lipids that parallels MPO results but is slightly more sensitive for the myeloid lineage.

Specific Esterase (CAE)

A stain using Naphthol AS-D chloroacetate that specifically identifies the granulocytic lineage; often positive in Auer rods.

Non-Specific Esterase (NSE)

A stain using $\alpha$-Naphtyl that is strongly positive in monocytes (M4/M5) and focal/dot-like in T-lymphoblasts.

NaF (Sodium Fluoride) Inhibition

A technique used with NSE; monocytic isoenzymes are fluoride-sensitive (become negative), while myeloid isoenzymes are fluoride-resistant.

Periodic Acid-Schiff (PAS) in AML M6

Leukemic erythroblasts show a characteristic strong positive reaction in COARSE BLOCKS, which differentiates them from normal erythroblasts.

Acid Phosphatase

A cytochemical stain used specifically to identify T-ALL, which shows focal positivity.

Double Esterase Stain

A combined stain (CAE and NSE) used on the same slide to confirm the dual lineage (granulocytic and monocytic) in AML M4.

PPO (Platelet Peroxidase)

An enzyme detected by electron microscopy in the nuclear envelope and ER of megakaryoblasts; essential for M7 diagnosis.

MDS-SF3B1

A WHO 2022 genetic category for Myelodysplastic Neoplasms defined by the presence of the $SF3B1$ mutation and low blasts ($<5\%$).

CCUS

Clonal Cytopenia of Undetermined Significance; recognized as a precursor entity to MDS or AML.

Terminal Deoxynucleotidyl Transferase (TdT)

An intranuclear enzyme present only in immature lymphoblasts; it is negative in mature B-ALL (L3), plasma cells, and mature lymphocytes.