Staging is used to determine the extent of a cancer spread in patients. The type of cancer should first be ascertained before undergoing staging so that a more informed approach can be undertaken. The cancer type is determined through biopsy and cytologic or histopathologic investigation of a sample. It is important to establish the stage of cancer as it is used to create a treatment plan and indicate prognosis. Staging should be completed before starting corticosteroid treatment as it can prevent an accurate reading.
Certain data points are necessary to attain before determining the overall cancer stage. These include:
TNM system classifies the stage of cancer by analysing 3 components: the primary tumour (T), lymph nodes (N), and metastases (M). These components are categorised into subsections.
Once the severity of each of these components has been determined, the overal stage can be interpreted.
Lymphoma has a unique staging system as it is inherently spread throughout the body due to being a cancer of the lymphatic system. Therefore, the stages are not based on metastases but rather the organs involved and clinical signs. Stage 1 dictates the involvement of one lymph node and stage 2 dictates the involvement of multiple nodes in one region. Stage 3 is categorised by general peripheral lymphadenopathy, stage 4 dictates involvement with the liver or spleen, and stage 5 is categorised by involvement with bone marrow or other organ systems. Substage a is used for patients without systemic signs and substage b is for those showcasing systemic signs.
Staging usually begins with physical examinations. These examinations can determine the size, location and mobility of the tumour. They may also determine if lymph nodes are involved, however, physical examinations alone cannot confirm the extent of lymph node interaction. If the tumour is internal, imaging may be required to assess the full extent of the cancer.
Complete blood count, serum biochemistry panel, and urinalysis tests should be carried out early to gain general data about the patient.
Many imaging types can be used in staging. Radiography can be used to quickly gain an overview of the tumours present. Ultrasonography can visualise the outlines of organs and lymph nodes. This makes its most helpful as a guide when performing aspiration which may be necessary to determine if cells present are cancerous. CT scans show a high definition of structures and are most efficient for visualising metastases. While MRI scans are also high definition, MRI scans are only necessary for brain tumours in animals.
Cytology and histopathology are used to confirm what physical examination and imaging cannot. Assessment of multiple lymph nodes should be undertaken as cancer spread through the lymphatic system can be highly variable. Cytology provides information by examining the microscopic cell appearance. These cells can be easily provided from fine-needle sampling and do not always require biopsy. Cytology can be used to ascertain the cell type, however, it cannot determine the tumour grade. Histopathology analyses tissue structure and is used to establish tumour grade from a biopsy sample.
Lymphoma can spread anywhere throughout the body, therefore multiple diagnostic tests are needed. 3-view thoracic radiographs should be completed. Cytology can be used to diagnose lymphoma, however, histopathology can be used when cytology is questionable, or when nodes are solitary or slow growing. Advanced imaging (CT or MRI scans) should be used to more accurately confirm location after the radiograph.
Mammary gland tumours can be detected from a 3-view thoracic radiograph as they are located within the breast tissue. Aspiration should be used to distinguish malignant tumours from benign. Regional lymph node aspiration should also be applied to determine lymph node involvement.
Histopathology should be used to determine tumour grade. Aspiration of regional lymph nodes should be completed. Aspiration of the spleen and liver should also be completed if they are enlarged or have nodal metastases as the mast cell metastases pass through the lymphatic system. 3-view thoracic radiographs should be performed.
Oral malignant melanoma is the most common form of melanoma in animals. They are common in lungs and lymph nodes, therefore 3-view thoracic radiographs should be performed. Aspiration and possible surgical removal of mandibular lymph node may be necessary for histopathology. CT or MRI scans may also be used to aid in surgical planning.
Splenic hemangiosarcoma is one of the most common forms of hemangiosarcoma. Anaemia is a factor to be looked for in lab tests. Abdominal ultrasonography and 3-view thoracic radiographs should be performed. Metastases are likely to be found in liver and lungs.
A referral to an oncology specialist may be considered for multiple reasons. Referrals are appropriate when pet owners wish to have a greater range of treatment options or want to proceed with treatment that the primary care veterinarian cannot provide. Additionally, referrals are also appropriate for clients who want to participate in clinical trials that primary care veterinarians do not have access to. Before engaging with a specialist, the client’s emotional attachment and financial resources should first be considered.
Animals diagnosed with a higher stage have a lower survival rate. For example, for each stage of oral malignant melanoma, the median amount of days survived after treatment with curative-intent surgery has been studied. Stage 1 has a median survival time of 874 days, stage 2 has 818 days, and stage 3 has 207 days. Stage 4 was not treated in this study.
Proper communication with pet owners regarding staging is a crucial component of treating animals with cancer. An explanation is necessary, as the client’s full understanding of the situation will aid in determining how they wish to proceed with treatment. However, revealing the stage of a pet can be an emotional and confronting experience for pet owners, especially those who may not have realised the severity of their pet’s condition. For this reason, clinicians should be patient and empathetic in their explanations. Some clinicians may find that relating the stages of animal cancer to that of humans can improve the client's comprehension of the topic.
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