Lymphoma

 

Etiology 

• The exact cause of lymphoma in dogs is not fully understood, but it’s believed to be multifactorial.

• Potential factors include:

  • Infections: Viruses or bacteria may play a role.

  • Environmental factors: Exposure to certain chemicals, such as phenoxyacetic acid herbicides, or strong magnetic fields.

  • Genetic mutations: Chromosomal changes or genetic abnormalities.

  • Immune system issues: Abnormal immune responses may contribute.

• Genetic studies have shown that lymphoma in dogs can be classified into different groups based on how aggressive they are biologically.

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Clinical Signs

• Generalized Lymphadenopathy (swollen lymph nodes):

  • 80-85% of dogs with lymphoma show non-painful, enlarged lymph nodes that are easily felt under the skin.

  • Affected lymph nodes are typically movable and firm.

• Organ-Specific Symptoms:

  • Alimentary lymphoma (affecting the digestive system):

    • Vomiting, diarrhea, weight loss, and poor appetite (due to malabsorption of nutrients).

    • Severe GI signs with widespread involvement of the intestines.

  • Mediastinal lymphoma (affecting the chest):

    • Breathing difficulties, fluid accumulation in the chest (pleural effusion), and possibly issues with the heart or veins (e.g., cranial vena cava syndrome).

    • Some dogs may also develop excessive thirst and urination due to high calcium levels (hypercalcemia).

  • Cutaneous lymphoma (affecting the skin):

    • Raised, ulcerated nodules or scaly, diffuse skin lesions, especially near the mucous membranes or lymph nodes.

  • Other signs:

    • If lymphoma affects other organs, signs may include blindness (eyes), seizures (CNS), kidney failure (renal), or pain due to bone involvement.

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Diagnosis

• Physical Examination:

  • Enlarged, non-painful lymph nodes may suggest lymphoma.

• Fine-Needle Aspiration (FNA):

  • A needle is used to take a sample from the swollen lymph nodes for cytologic (microscopic) examination.

  • Lymphoma typically shows a uniform population of abnormal lymphoid cells.

• Biopsy and Histology:

  • A tissue sample can be examined under a microscope to determine the lymphoma’s type and grade (high or low).

• Molecular Testing:

  • Flow Cytometry: Identifies lymphoma based on cell size and markers on the surface of the cells.

  • PCR (Polymerase Chain Reaction): Detects genetic markers to confirm lymphoma’s neoplastic (cancerous) origin.

• Staging:

  • Staging helps determine how far the cancer has spread and guides treatment decisions.

  • Imaging and bone marrow evaluation may be needed to assess the extent of the disease.

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Treatment

• Chemotherapy:

  • Systemic chemotherapy is the primary treatment and is effective for most types of lymphoma, achieving a high initial response rate (around 90%).

  • Common chemotherapy drugs include cyclophosphamide, doxorubicin (hydroxydaunorubicin), vincristine, and prednisone (CHOP protocol).

  • Lomustine, mitoxantrone, and rabacfosadine are other chemotherapy options.

  • The goal is to reduce symptoms and improve quality of life, as remission is often temporary (with relapses occurring in most cases).

  • Median survival time with chemotherapy is about 12 months for B-cell lymphoma and 6-8 months for T-cell lymphoma.

• Radiotherapy:

  • Can be used in conjunction with chemotherapy, especially for localized tumors or specific organ involvement (e.g., mediastinal lymphoma or cutaneous lymphoma).

• Prednisone:

  • Can help manage symptoms and may induce short-term remission (1-2 months). However, it is not curative and resistance can develop.

• Autologous Bone Marrow Transplant:

  • A highly aggressive treatment that involves high-dose chemotherapy and the reinfusion of the dog's own bone marrow after it has been removed and treated. This is available at specialized centers.

• Indolent (Low-Grade) Lymphoma:

  • These cases progress more slowly. Chlorambucil and prednisone are used for long-term management, and dogs can survive for over 2 years with treatment.

• Surgical Resection:

  • For dogs with focal alimentary lymphoma (localized intestinal involvement), surgery to remove the tumor may be effective, followed by chemotherapy.

• Other Options:

  • Verdinexor: A newer drug (FDA-approved for canine lymphoma in 2021) that may help in certain cases, though results have been less promising than traditional chemotherapy.

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Prognosis

• Without treatment, dogs with lymphoma typically live only 4-6 weeks.

• Chemotherapy can significantly improve the quality of life and extend survival, with some dogs living for a year or more.

• The prognosis varies widely depending on lymphoma type, organ involvement, and response to treatment, with high-grade T-cell lymphoma generally having a poorer prognosis than B-cell lymphoma.

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​Leukemia

 

Etiology

• Leukemia refers to the presence of cancerous (neoplastic) blood cells in the bone marrow or peripheral blood.

• It’s rare in dogs (less than 10% of hematopoietic cancers) and more common in cats (15-35% of cases).

• The exact causes of leukemia in animals are mostly unknown, but Feline Leukemia Virus (FeLV) is a known risk factor in cats.

• There are no proven environmental or genetic causes identified for leukemia in small animals, although factors like toxins or immune dysfunction may play a role in some cases.

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Classification of Leukemia

Leukemia is classified based on:

1. Cell type (lineage) – whether the leukemia involves lymphoid or myeloid cells.

2. Clinical course – whether the leukemia is acute (fast-growing) or chronic (slow-growing).

3. Cell differentiation – how mature the cancer cells are.

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Types of Leukemia

• Lymphoproliferative Disorders:

  • Acute Lymphoblastic Leukemia (ALL) – aggressive, immature lymphoid cells.

  • Chronic Lymphocytic Leukemia (CLL) – slower, more differentiated lymphoid cells.

• Myeloid Neoplasms:

  • Acute Myeloid Leukemia (AML) – fast-growing, often poorly differentiated cells.

  • Chronic Myeloproliferative Disorders – slower, more mature cells, including Chronic Myeloid Leukemia (CML), Polycythemia Vera, and Essential Thrombocythemia.

  • Myelodysplastic Syndromes (MDS) – a precursor to leukemia, with abnormal cells in the bone marrow but not yet fully cancerous.

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Clinical Signs

• Chronic Leukemia (e.g., CLL):

  • Often asymptomatic for long periods.

  • If symptoms appear: mild lethargy, anorexia, weight loss, mild lymphadenopathy (swollen lymph nodes), and splenomegaly (enlarged spleen).

• Acute Leukemia (e.g., ALL or AML):

  • More severe symptoms:

    • Prominent organ enlargement (e.g., spleen, liver, lymph nodes).

    • Hemorrhages (nosebleeds, bruising).

    • Neurological symptoms (seizures, weakness).

    • Fever and cytopenias (low blood cell counts) leading to weakness, infection, or anemia.

• General Symptoms:

  • Dogs and cats may show systemic symptoms like lethargy, poor appetite, and weight loss.

  • Chronic leukemias tend to show milder signs, while acute forms progress rapidly and can be life-threatening.

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Diagnosis 

• Blood Tests:

  • In many cases, leukemia can be diagnosed by finding a high number of neoplastic cells in the peripheral blood.

• Bone Marrow Biopsy:

  • If blood tests don’t show conclusive results, a bone marrow biopsy is often needed. The presence of more than 30% blast cells in the marrow typically confirms acute myeloid leukemia (AML).

• Cell Lineage Identification:

  • Special tests like cytochemistry, immunocytochemistry, and flow cytometry may be required to determine the exact type of leukemia.

  • Immunophenotyping markers (e.g., CD79a, CD3, CD11b) help identify the specific lineage of leukemia (whether it’s from lymphoid or myeloid cells).

• Differential Diagnosis:

  • Leukemia can be confused with other conditions like lymphoma or myelodysplastic syndromes (MDS). Clonality tests may help in some cases but are not widely available.

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Treatment

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Acute Leukemia:

• Aggressive Chemotherapy is needed to suppress the malignant cells and restore normal hematopoiesis (blood cell production).

  • CHOP protocol (cyclophosphamide, doxorubicin, vincristine, prednisone) is commonly used for acute lymphoblastic leukemia (ALL), although remission rates are typically less than 30%.

  • Supportive Care (e.g., antibiotics, fluids, blood transfusions) is also critical to manage complications like infections, anemia, or bleeding.

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Chronic Leukemia:

• Chronic Lymphocytic Leukemia (CLL) is slower-growing and may not require immediate treatment unless there is significant organ enlargement, anemia, or other complications.

  • Chlorambucil (an oral chemotherapy drug) is the most commonly used treatment for CLL. It may be used alone or with prednisone for better results.

  • Complete remission is rare, but survival times can range from 1 to 3 years with good quality of life.

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Acute Myeloid Leukemia (AML):

• AML generally has a poor response to therapy, and no standard protocol has been established. However, cytosine arabinoside combined with doxorubicin or cyclophosphamide is commonly used.

  • Maintenance therapy with a COAP protocol (cyclophosphamide, vincristine, cytosine arabinoside, prednisone) can be tried after remission.

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Chronic Myeloproliferative Disorders:

• Hydroxyurea is often used to treat conditions like chronic myeloid leukemia (CML), essential thrombocythemia, and polycythemia vera.

• Phlebotomy (removing excess blood) may also be used for polycythemia vera.

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Other Treatment Options:

• Radiotherapy and immunotherapy are under investigation as alternative treatments.

• Bone marrow transplantation may offer a curative option in certain cases, but this is still experimental.

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Prognosis

• Acute Leukemia (especially ALL and AML) is usually fatal without aggressive treatment, with a poor overall prognosis due to the rapid progression of the disease.

• Chronic Leukemia (like CLL) may allow dogs or cats to live for several years, especially if treated early and managed well.

• Survival time varies greatly, but with treatment, CLL can be managed for 1-3 years, while AML generally has a much shorter survival rate.