21. Oncology

CHAPTER 21. Oncology

Patricia A. Schenck




ONCOLOGY PRINCIPLES






I. Presentation




A. Pay particular attention to the age, sex, breed, and species, as this information often helps with the diagnosis


B. The location of the tumor, the duration, and growth rate are also important


C. A complete physical examination is necessary to assess the overall health of the animal. Regional lymph nodes should be carefully palpated and the lungs assessed


II. Diagnosis




A. Laboratory evaluation




1. A complete blood cell count (CBC), serum biochemistry profile, and urinalysis should be performed to assess overall health


2. Other laboratory tests are performed as needed (e.g., feline leukemia virus [FeLV], bone marrow aspirate, adrenal function tests)


B. Diagnostic imaging




1. Radiographs (thorax, abdomen, skeleton) should be taken to determine the presence of metastases


2. Ultrasound is most useful to visualize the abdomen


C. Cytology




1. Can provide rapid and inexpensive diagnostic information


2. Do not overinterpret cytology preparations


3. Definitive diagnosis most often requires histopathology


D. Biopsy




1. Larger samples provide a more accurate diagnosis


2. Fix tissue samples in 10% buffered formalin


3. Histologic samples should contain the neoplastic tissue with a margin of normal tissue


III. Principles of therapy




A. Surgery




1. Most useful for localized tumors


2. Resect all neoplastic tissue, if possible with wide margins


3. Prevent surgical spread of cancer cells




a. Minimize the manipulation of the tumor


b. Protect healthy tissues from tumor cell contamination with the use of barrier drapes


c. Change gloves, drapes, and instruments during surgery if necessary


B. Radiotherapy




1. Used for local or regional tumors


2. Can be used before surgery to reduce the size of the tumor, concurrently with chemotherapy, or postoperatively


3. The effectiveness of radiation therapy can be improved by chemotherapy-induced radiosensitization


4. Need to irradiate potentially affected tissues and a normal tissue margin


5. Frequent small doses of radiation allow for repair of normal cells and decreased radiation toxicity


6. Radiation is most effective when the tumor size is small


C. Chemotherapy




1. Most often used for regional or disseminated neoplasms


2. Some tumors are quite chemosensitive (lymphoid neoplasia)


3. Administer chemotherapy agents at the maximal tolerated dose


4. Continue chemotherapy after apparent remission because a microscopic tumor remains after the tumor can no longer be physically detected


5. Tumors can become drug resistant; the larger the tumor, the more likely that it will become resistant


6. Patients should be reevaluated at regular intervals post therapy


D. Nutritional management




1. Anorexia is common (cancer cachexia) and may be related to the side effects of therapy or to tumor-produced anorexigenic substances


2. Provide enteral or parenteral feeding if patients do not eat for more than 5 days or have an acute loss of 10% or more of body weight


3. Malnourished patients show hypoalbuminemia, lymphopenia, and anemia


4. Malnutrition adversely impacts the immune system, delays wound healing and cell repair, and increases morbidity and mortality


E. Pain management




1. Acute vs. chronic; treatment vs. tumor-related


2. Contributes to anorexia, weight loss, reduced mobility, depression


3. Prevention or early treatment of pain is more effective than treating severe or chronic pain


4. Provide pain relief with minimal sedation and other side effects


LYMPHOID NEOPLASIA






I. Lymphoma




A. Cause




1. Retrovirus can cause lymphoma in the cat, chicken, and human


2. In the cat, both FeLV and feline immunodeficiency virus (FIV) can cause lymphoma


3. In the dog, a viral etiology has not been established


4. Genetics may play a role; exposure to environmental carcinogens may also play a role in development

































Table 21-1 World Health Organization Clinical Staging for Domestic Animals with Lymphoma
World Health Organization (WHO). TNM Classification of Tumors in Domestic Animals. Geneva, 1980, WHO.
Stage Criteria
I Single lymph node
II Multiple lymph nodes in a regional area
III Generalized lymphadenopathy
IV Liver or spleen involvement (with or without stage III)
V Bone marrow or blood involvement or any nonlymphoid organ (with or without stages I to IV)
Substage a Without clinical signs of disease
Substage b With clinical signs of disease



















































Table 21-2 Characteristics of Feline Lymphoma by Anatomic Site
From Ettinger SJ, Feldman EC, editors. Textbook of Veterinary Internal Medicine, 6th ed. St Louis, 2005, Saunders.
*FeLV-positive cats tend to be younger, and the cancer is more commonly of T-cell derivation.
From Ettinger SJ, Feldman EC, editors. Textbook of Veterinary Internal Medicine, 6th ed. St Louis, 2005, Saunders.
Anatomic Site Relative Frequency Age T-Cell Association FeLV Positive
Alimentary 50%-70% ∼10-14 yr High Low (5%)
Multicentric 10%-25% Depends on feline leukemia virus (FeLV) status* Depends on FeLV status* Approximately one third
Mediastinal/thymic 10%-20% Young High High (>80%)
Nasal ∼10% Aged Low Low
Renal 5%-10% Middle-aged Low to moderate Low to moderate
Other 5%-25% Mixed Mixed Mixed




1. Multicentric lymphoma is the most common form in the dog. Enlarged lymph nodes are typically palpated. Other clinical signs include weight loss, decreased appetite, polyuria (PU)/polydipsia (PD), and lethargy. Enlargement of the liver and spleen are commonly seen


2. Alimentary lymphoma is associated with gastrointestinal (GI) signs such as vomiting, diarrhea, weight loss, and lethargy


3. Mediastinal lymphoma usually causes respiratory signs. Most mediastinal lymphomas are associated with hypercalcemia


4. Cutaneous lymphoma varies in appearance. Many are pruritic


5. Extranodal lymphoma includes lymphoma in the eye, central nervous system (CNS), bones, heart, kidneys, urinary bladder, and nasal cavity


6. B-cell vs. T-cell lymphoma




a. In the dog, most are B-cell lymphomas. T-cell lymphoma is associated with hypercalcemia, and cranial mediastinal tumors


b. Most FeLV associated lymphomas in cats are T-cell lymphomas


7. Most animals are middle-aged or older


C. Diagnosis




1. Physical examination




a. Palpate all lymph nodes


b. Evaluate organ involvement, especially liver or kidney involvement


c. Bone marrow involvement can cause hematologic abnormalities


d. Ophthalmic problems such as uveitis, hemorrhage, and ocular infiltration occur in about 33% of dogs with lymphoma


2. Laboratory evaluation




a. Immature lymphocytes are usually seen in the circulation


b. Normocytic, normochromic, nonregenerative anemia is common


c. Bone marrow aspirate may show neoplastic lymphocytes


d. Hypercalcemia is seen in about 20% of those with lymphoma


e. Increased blood urea nitrogen and creatinine may be seen with kidney involvement


f. If there is liver involvement, liver enzymes may be increased


g. Most cats with mediastinal or multicentric lymphoma are FeLV positive



4. Histopathology of lymph nodes is recommended. With cytology, neoplasia can be difficult to distinguish from benign lymphadenopathy


5. Other tests




a. May need to do an exploratory laparotomy


b. Cerebrospinal fluid cytological evaluation may help in the diagnosis of CNS lymphoma in the dog


6. Differential diagnosis




a. Lymphadenopathy differentials include infectious diseases, immune-mediated diseases, and other metastatic neoplasia


b. Differentials for alimentary lymphoma include lymphocytic enteritis, other intestinal neoplasias, granulomatous disease, and hypereosinophilic syndrome


c. Differentials for mediastinal lymphoma include thyroid tumors, heart base tumors, thymoma, and pulmonary granulomatosis


d. Differentials for cutaneous lymphoma include pyoderma, immune-mediated disorders, parasitic skin disorders, and other cutaneous neoplasia


D. Treatment




1. Require chemotherapy. Without treatment, most live only 4 to 6 weeks after diagnosis


2. With chemotherapy, up to 90% of dogs and 70% of cats enter remission and survive up to a median of one year. Cures are uncommon, but about 25% can live 2 or more years. If cats can achieve remission, they can survive for long periods


3. Cats have fewer adverse effects unless they are treated with doxorubicin. Do not give doxorubicin to cats with renal disease


4. Combination protocols tend to be more effective, with longer remissions and survival time; they are also more costly and more time-consuming


5. Protocols: A number of protocols are available. The most common protocols are discussed below:




a. The CHOP combination protocol (C = cyclophosphamide, H = hydroxydaunorubicin [doxorubicin], O = Oncovin [Vincristine], P = prednisone) (University of Wisconsin-Madison Short Protocol). Patients are off all medication after 19 weeks. l-asparaginase is no longer a part of this protocol; l-asparaginase is reserved for “rescue”


b. Doxorubicin used alone achieves remission in about 70% of dogs


c. Prednisone used alone is inexpensive, but the survival time is only about 2 months


6. If cytopenia is present, prednisone, l-asparaginase, and vincristine are used, as these agents tend to spare the bone marrow. However, if cytopenia is the result of bone marrow infiltration, aggressive chemotherapy is required


7. Reinduction and Rescue therapy




a. If a patient that has previously been in remission has a recurrence of lymphoma, the same protocol that was used initially should be reintroduced. After reinduction, the length of remission is typically half that initially used


b. Rescue therapy is instituted when remission cannot be obtained with the regular protocol. Drugs used for rescue include mitoxantrone, l-asparaginase, lomustine, and actinomycin-D. Remissions achieved with a rescue protocol are generally short


8. Small cell lymphomas tend to be more resistant to therapy. Chlorambucil and prednisone therapy appear helpful


9. Surgery combined with radiation therapy and chemotherapy may be beneficial in CNS lymphoma


10. Cutaneous lymphoma is resistant to chemotherapy and may be able to be treated with surgery and radiotherapy. Lomustine, retinoic acid, or l-asparaginase may be beneficial


E. Prognosis




1. Dogs




a. Stage V, or substage b, are associated with shorter remission and survival times


b. T-cell lymphoma has a shorter remission and survival time


c. Female dogs may have a longer survival time


d. Hypercalcemia is associated with T-cell lymphoma and a worse prognosis


e. GI lymphoma, disseminated cutaneous, or leukemic forms have a poorer prognosis


2. Cats




a. The higher the clinical stage, the poorer the prognosis


b. FeLV positive cats have a poorer prognosis


c. The presence of leukemia, anemia, neutropenia, and sepsis worsen the prognosis


d. Cats that achieve remission early have a better prognosis

Tags:
Apr 6, 2017 | Posted by in GENERAL | Comments Off on 21. Oncology

Full access? Get Clinical Tree
Get Clinical Tree app for offline access