Overview

Oncology deals with prevention, diagnosis, and treatment of cancer. Clinical oncology consists of three primary disciplines: medical oncology (the treatment of cancer with medicine including chemotherapy), surgical oncology (the surgical aspects of cancer including biopsy, staging and surgical resection of tumors), radiation oncology (the treatment of cancer with therapeutic radiation).

Each oncology case is medically unique, hence the approach must also be patient-specific consisting of the following components:

  • Diagnosis
  • Staging (determining the extent of local disease and pre of regional or distant metastasis)
  • Therapeutic intervention (based on tumor type, histologic grade, and stage)
  • Provisions for patient and personnel safety in handling chemotherapy agents
  • Referral to an oncology speciality practice like MaxVets when appropriate
  • A strong emphasis on client support.

Because cancer is often a disease of older pets, which is the time of life when the pet-owner relationship is usually the strongest, a satisfying outcome for all parties involved is highly dependent on good communication between the entire healthcare team and the client, particularly when death or euthanasia of the patient is being considered.

Cancer Statistics

  • Cancer is one of the leading causes of death in companion animals such as dogs and cats.
  • It is particularly common in animals that live 10 years or longer but can occur at any age.
  • Skin tumors are one of the most frequently diagnosed type of tumor in pets (may be due to constant exposure of animal skin to the sun and the external environment and because they are easily observed from the outside). Dogs are 35 times more likely to suffer from skin cancers than humans.

At MaxVets, mast cell tumors, lymphomas, adenocarcinoma and osteosarcomas are the most commonly encountered.

Diagnosis of Tumor Type

Once the possibility of a neoplastic process (both malignant or benign growths) is suspected, determination of the tumor type serves as the basis for all subsequent steps in patient management.

  • No confirmed diagnosis can be made be palpation alone.
  • A biopsy is the basic tool that allows removal and examination of cells from the body to determine the presence, cause, or extent of a disease process.
  • Samples for analysis are obtained by fine-needle sampling (for cytological examination) which can be performed safely for the majority of external tumors without anesthesia or sedation. Sometimes surgical excision biopsies are advised for diagnosis and staging, which requires complete general anesthesia.
  • Pet owners should be prepared for repeated imaging and staging before the decision for final treatment options is made.

Common Cancers

In dogs:

  • Anal sac carcinoma: It occurs in the anal sac and is locally aggressive, hence, excision is difficult. It progresses slowly and is difficult to observe by symptoms alone unless renal function is compromised.
  • Lymphoma: It is multicentric (node, liver, and spleen) and occurs in bone, CNS (Central Nervous System), mucocutaneous tissue and skin. It is, thus, hard to treat.
  • Mammary gland cancer: It occurs in one or more mammary glands and is most common type of cancer in females. Early spaying is advisable to prevent these tumors.
  • Mast cell tumor: It occurs in skin and subcutaneous tissue and is locally invasive.
  • Oral malignant melanoma: It occurs in the oral cavity and is more metastatic in lymph nodes than lungs.
  • Osteosarcoma: It is a rare type of skeletal metastases observed in bones (proximal humerus, distal radius, distal femur, proximal and distal tibia).
  • Soft tissue sarcoma: These are mesenchymal tumors occurring in skin and subcutaneous tissues. It is locally invasive.
  • Splenic hemangiosarcoma: It is a highly metastatic splenic masses which cannot be definitively distinguished from HSA (Hemangiosarcoma) prior to treatment.

In cats:

  • Lymphoma: Commonly occurs in thymus, GI tract, liver, spleen, kidney and rarely mucocutaneous tissue. It is considered a systemic disease.
  • Mammary gland cancer: It occurs in mammary glands and is highly metastatic and locally aggressive.
  • Squamous cell carcinoma: It may be oral or cutaneous. It is extremely locally aggressive in case of oral and progresses slowly in case of cutaneous.

Soft tissue sarcomas: Occurring in cutaneous and subcutaneous tissue, it is extremely locally aggressive.

TREATMENT OPTION

Chemotherapy

  • Commonly used treatment
  • Types: Conventional chemotherapy (also called maximally tolerated dose chemotherapy), metronomic chemotherapy (uninterrupted administration of low doses of cytotoxic drugs at regular and frequent intervals), and targeted chemotherapy using tyrosine kinase inhibitors (TKIs are anti-cancer drugs that block signal transduction thereby preventing tumor growth)
  • The most common side effects of these include gastrointestinal, including diarrhoea, loss of appetite, and occasional vomiting, anorexia, hair loss nausea and bone marrow suppression.
  • Other less common side effects are hepatotoxicity, neutropenia, muscle pain and coagulopathies.

Immunotherapy

  • For increasing immunity towards cancer.
  • However, most of such vaccines are still being investigated in clinical trials.
  • Its success depends on the combination treatment with other treatment modalities like radiation therapy and chemotherapy.

Adjunctive Therapy

  • For improving the life of the patients.
  • Its goal is to maintain quality of life by limiting treatment side effects, pain, and discomfort.
  • Variety of antiemetics are available today in veterinary medicine.
  • Nutrition also plays a significant role in treatment, hence the nutritional status of all oncology patients should be routinely assessed.
  • Pain management is essential since even the treatment therapies like radiation and surgery are associated with pain issues and concurrent disease. So, to adequately control pain, a combination of more than one pain medication is routinely required.

Radiation Therapy

  • Utilizes ionizing radiation to kill cancer cells.
  • The goal is to eradicate all the viable tumor cells within the patient.
  • Surgery:
  • As a general rule, if a primary tumor can be completely excised with acceptable morbidity, surgery is the best choice of treatment.

Locally recurrent tumors are more difficult to remove.

Follow Up And Care

  • Assessment of response: It is viewed in context of the original intent of therapy, cure or palliation.
  • Post radiation therapy monitoring: To avoid the possibility of recurrence, metastasis, new tumor development, or complications of initial therapy.
  • Maintenance chemotherapy: To prolong survival even if it is not curative.

Management of recurrent or metastatic disease: Goals are often dynamic and impacted by extent of disease and expectations for the quality of life of the patient.