WBCs, LNs, spleen, and thymus (Condensed) 2026

Sequence of sites for hematopoiesis in the developing fetus

Yolk sac → aorta-gonad mesonephros (mesoblastic phase) → fetal liver (hepatic phase) → bone marrow (medullary phase)

Site presumed to be the most active in hematopoiesis in adults and with the highest cellularity

Vertebrae

Enzyme found in mature leukocyte; high number of this enzyme is associated with increased number of mature WBC

Leukocyte alkaline phosphatase (LAP) - Increased in leukemoid reactions and low in CML with abnormal leukocytes

Condition associated with basophilic leukocytosis

Chronic myeloid leukemia

Most common cancer in children

Acute lymphoblastic leukemia (ALL)

Most common type of ALL

B-lymphoblastic leukemia (85%)

Most common mutation associated with B-ALL

t(12;21) → ETV6::RUNX1 fusion

Common sites of metastases for B-ALL (2)

CNS and testicles

Translocation seen in acute promyelocytic leukemia (APML)

t(15;17) - PML:RARA fusion

Type of leukemia associated with Auer rods (needle-like cytoplasmic azurophilic granules) and ****** cells

Acute promyelocytic leukemia (APML). This is a hematological emergency

Type of leukemia associated with disseminated intravascular coagulation due to (+) numerous azurophilic granules rich in procoagulant substances (e.g. tissue factor, etc.)

Acute promyelocytic leukemia (APML)

Medication given to patients with acute promyelocytic leukemia (APML) to induce maturation of immature malignant WBCs

ATRA (all-trans retinoic acid)

Most common leukemia of adults in the Western world (~60 years old); (+) smudge cells on smearing

Chronic lymphocytic leukemia (CLL)

Phenomenon of the transformation of CLL to diffuse large B cell lymphoma

Richter syndrome

Translocation and gene mutation associated with chronic myeloid leukemia

t(9;22) → BCR::ABL1 fusion. t(9;22) is also seen in ALL but with a different breakpoint region from that of CML.

Leukemia associated with lymphocytes in blood with circumferential hair-like projection; with a hypocellular arrow with fibrosis and neoplastic lymphocytes

Hairy cell leukemia

Pertinent positive cytochemistry finding in patients with hairy cell leukemia

Tartrate-resistant acid phosphatase (TRAP)

Virus associated with Hodgkin lymphoma development

Epstein Barr Virus

Tumor cell pathognomonic of Hodgkin lymphoma; large cells with binuclear/bilobed nuclei with dark centers of chromatin and pale halos (Owl's eye nucleus)

Reed-Sternberg Cells

Positive immunohistochemistry finding in classic Hodgkin lymphoma (2)

(+) CD15 and CD30

Positive immunohistochemistry finding in nodular lymphocyte-predominant Hodgkin lymphoma

(+) CD20

Most common subtype of Hodgkin lymphoma; affecting mostly adolescents and young adults

Nodular sclerosis HL. (+) Lacunar RS cells, deposition of collagen in bands that divide the involved nodules into circumscribed nodules

Subtype of Hodgkin lymphoma associated with classic Reed Sternberg cells + diffuse heterogenous inflammatory infiltrate; (+) B symptoms

Mixed cellularity HL

Least common subtype of Hodgkin lymphoma, often in older men, and HIV-positive persons in lower-income countries

Lymphocyte-depletion HL

Subtype of Hodgkin lymphoma associated with lymphohistiocytic or popcorn cells, (+) cervical and axillary lymphadenopathy; affecting males <35 years old

Nodular lymphocyte predominant HL

Subtype of Hodgkin lymphoma with the best prognosis

Nodular sclerosis HL

Subtype of Hodgkin lymphoma with the worst, unfavorable prognosis

Lymphocyte depletion HL

Protein overexpressed in patients with t(11;14) translocation in mantle cell lymphoma

Cyclin D1 - This is the protein that regulates the transition from G1 to S phase in the cell cycle via the activation of cyclin-dependent protein kinases.

Most common form of indolent non-Hodgkin lymphoma in the US

Follicular lymphoma

Translocation associated with follicular lymphoma

t(14;18)

Protein overexpressed in follicular lymphoma

BCL2. This is an anti-apoptotic protein, thus its overexpression allows the cancer cells to evade apoptosis.

Non-Hodgkin lymphoma associated with chronic inflammatory disorders (e.g., H. pylori gastritis, Sjogren syndrome, Hashimoto thyroiditis)

Marginal zone lymphoma (MZL) of mucosa-associated lymphoid tissue (MALT)

Most common subtype of non-Hodgkin lymphoma, usually presenting as a rapidly enlarging extranodal mass

Diffuse large B cell lymphoma

Translocation involved in Burkitt lymphoma

t(8;14)

Histological pattern seen in Burkitt lymphoma, associated with sheets of medium-sized atypical lymphocytes with tingible body macrophages

Starry-sky pattern - Due to the high mitosis and proliferative index

Cutaneous CD4+ T cell lymphoma

Mycosis fungoides

Aggregates of atypical CD4+ T cells within the epidermis that are indicative of mycosis fungoides

Pautrier microabscesses

Effect of multiple myeloma on the RBC, causing aggregations of erythrocytes with appearance of stack of coin appearance

Roleaux formation

Cause of rouleaux formation, renal failure, and frequent infections in patients with multiple myeloma

Production of abnormal immunoglobulins (M-protein)

Immunoglobulin inclusion in multiple myeloma with fiery red cytoplasm

Flame cells

Percentage of clonal bone marrow cells required to diagnose multiple myeloma

>10%

Myeloma-defining events (CRAB) (4)

HyperCalcemia, Renal failure, Anemia, Bone lesions

Type of proteinuria that characterizes multiple myeloma

Bence Jones proteinuria

Most common causes of death in multiple myeloma (2)

Infections > Renal failure

Group of clonal hematopoietic stem cell neoplasms characterized by impaired proliferation and differentiation of myeloid stem cells in the bone marrow; occurring mostly in the elderly population

Myelodysplastic syndrome

Peripheral blood smear finding of granulocytes that reduced segmentation (e.g. neutrophils with bilobed nuclei); seen in myelodysplastic syndrome

Psuedo-Pelger Huet anomaly

Common mutation seen in myeloproliferative neoplasms (e.g. polycythemia vera and essential thrombocytosis)

JAK2 V617 mutation

Abnormal proliferation of erythrocytes (frequently with leukocytosis or thrombocytosis - panmyelosis)

Polycythemia vera

Red cell morphology associated with primary myelofibrosis

Dacrocytes (teardrop cells) - Due to squeezing from the fibrotic marrow

Condition characterized by one or more cytopenia caused by pooling, sequestration, and premature destruction of blood cells in an enlarged spleen

Hypersplenism

Autoimmune condition associated with thymic follicular hyperplasia (increased secondary follicles within the thymus)

Myasthenia gravis. An antigen in thymic myoid cells is thought to trigger autoimmunity in myasthenia gravis.

Most common thymic epithelial tumor; especially at the 5th and 6th decades of life

Thymoma