A Systematic Approach to Cancer in Pets: Clinical Evaluation and Staging
Margaret C. McEntee, DVM, DACVIM (oncology),
DACVR (radiation oncology)
In order to provide relevant information about cancer treatment options to clients, information regarding onset, progression and anatomic extent of the tumor must be systematically collected. This presentation will highlight the importance of clinical data collection in the staging of cancer.
The first step is the acquisition of a thorough clinical history. There are times where the problem at hand has just been noticed and the client presents the next day for an appointment. However, often times the lump, bump or other change in clinical condition has been noticed and observed over a period of time. There are a number of questions that should be asked. The following will provide an example of questions to ask relative to a dog with a skin mass.
1 When did you first notice the mass?
2 How big was the mass when you first noticed it?
3 Has the mass grown, or changed in its rate of growth?
4 Has there been any bleeding or discharge?
5 Does it bother your dog? Has your dog been licking or scratching the site?
6 Are there any other changes that you have noticed?
Past Pertinent History
It is also important to determine if there have been any other previous medical problems, or any concurrent problems that may impact the ability to treat the current disease. For example, the knowledge that a cat has renal insufficiency/failure will preclude the use of doxorubicin, as it will likely exacerbate the condition. Questions should be asked as to if there have been any previous medical problems, or surgical procedures performed. The knowledge that a dog had a mast cell tumor in the past may alter the extent of the evaluation and/or staging of the current problem.
Many tumors more commonly affect animals of a certain age, sex or breed, and knowledge of this may aid in diagnosis. The following is a partial list of associations that have been made. All references are to the dog except where otherwise indicated.
A complete physical examination is the first step in patient evaluation. Particular attention is paid to the current complaint. Measurements of masses (three dimensions using calipers) and accurate descriptions are critical. It should be possible to read a medical record and picture where a mass is located, how big it is, what it looks like and what it's relationship is to the surrounding normal tissues. For a patient that has multiple masses a topographic map should be generated that shows the location and size of each of the masses. The regional lymph node should be palpated and a determination made as to its size and consistency. Is it normal in size, shape and consistency? Or is there any evidence that the lymph node is enlarged, firm and/or fixed in position? Any of the latter changes raises the index of suspicion that the tumor may have spread to the regional lymph node.
Patients with cancer are typically older but cancer can occur at any age. Routine blood work is done most commonly as a part of an overall health screen. Basic laboratory work that should be done includes a complete blood cell count, chemistry panel, and urinalysis. Regardless of the procedures and treatment to follow it is important to assess the patients overall health status. The initial blood tests can aid in the diagnosis of the primary condition, e.g., lymphoblastic leukemia or stage V lymphoma, with identification of a large number of blasts in the circulation. Additional testing may be indicated based on the results of the initial tests. Lymphoma patients not uncommonly have urinary tract infections secondary to their immune compromised status and a urine culture is important if there is evidence of a urinary tract infection. If the CBC reveals that the patient is thrombocytopenic then a coagulation panel may be indicated as well as potentially a bone marrow aspirate to assess the adequacy of the precursor cells (megakaryocytes) at the level of the bone marrow. This also brings to mind the concept of paraneoplastic syndromes in cancer patients. For instance a dog with a cranial mediastinal may have lymphoma or a thymoma and the chemistry panel may reveal that the patient is hypercalcemic. The following table outlines a number of paraneoplastic syndromes that may be identified on the initial screening blood work and the tumors that have been associated with each.
Regional lymph node evaluation
The regional lymph node should be evaluated by aspiration cytology and/or biopsy (incisional or excisional) under the following conditions:
1 Regional lymph node is enlarged, fixed and/or firm on palpation.
2 There is a high index of suspicion that the tumor may spread via the lymphatics to the regional lymph node (e.g., mammary gland carcinoma, mast cell tumor, etc.).
Aspiration cytology is the first step. A positive finding of metastasis provides evidence of metastasis but a negative result in some situations should be followed up with a biopsy. If the most important step in staging is the regional lymph node then a tissue biopsy and histopathology is warranted.
Three-view thoracic radiography is commonly utilized to assess patients for any evidence of pulmonary metastasis. Thoracic radiographs are often made prior to diagnosis of the primary tumor. It should be emphasized that once the primary tumor has been definitively identified then more directed staging and patient evaluation should be possible. It is also important to remember that the radiographic pattern of pulmonary involvement can vary depending on the primary tumor type. For instance pulmonary metastasis of canine splenic hemangiosarcoma can present as a diffuse interstitial pattern or the more commonly recognized nodular pattern. Both are possible. Thoracic radiographs may also reveal enlarged lymph nodes (evidence of metastasis), or identify a primary tumor (lung, cranial mediastinal lymphoma, etc.).
In older patients thoracic radiography may be part of the routine health screen and a means to assess the heart and lungs. Particularly for patients that are to undergo a full course of radiation therapy and multiple anesthetics it is important to ensure that there are no other underlying problems. Thoracic radiographs should be obtained even in patients where the primary tumor is unlikely to metastasize to the lung (e.g., hemangiopericytoma, mast cell tumor).
Many techniques are available. The specific method should as simply and safely as possible obtain an adequate sample for evaluation without compromising the subsequent definitive therapy. For instance, placement of the biopsy incision and tract within the region to be included in the radiation and/or surgical field is critical to the ultimate success of therapy. Biopsy techniques that are available include cutting forcep biopsies (often used for nasal tumors), cutting needle biopsies, punch biopsies, and incisional biopsies. Superficial masses can be readily biopsied by any of a number of different techniques. More deeply seated tumors may require endoscopic visualization and biopsy, ultrasound guidance, or surgical approach to the site (e.g., exploratory laparotomy) to obtain a tissue sample. One important point to discuss with owners is the possibility that when only a small portion of a tumor is sampled that the biopsy may be non-diagnostic. This is most notably possible with "blind" biopsy techniques as are used for bone tumors and nasal tumors.
Conventional radiography for tumor imaging can provide a useful screening tool. It has specific utility in the imaging of primary and metastatic bone tumors particularly of the appendicular skeleton. The main disadvantage of radiography results from the superimposition of overlying structures. For instance, imaging of nasal tumors using conventional radiography can provide information regarding areas of involvement and may show bony or turbinate lysis. However, imaging of nasal tumors is better suited to cross-sectional imaging modalities such as computed tomography (CT) or magnetic resonance imaging (MRI).
Ultrasonography is used routinely in staging cancer patients and may be the primary imaging modality for evaluation of the primary tumor. It provides information on the internal structure of organs based on differences in acoustic impedance. Sonography provides useful information not attainable with routine radiography because tissues with different acoustic impedances often have the same radiographic opacity. Ultrasonography has largely replaced abdominal radiography. Ultrasonographic identification of bowel-associated masses has also replaced barium studies. Ultrasound guided fine-needle aspiration biopsy can be useful in the diagnosis of gastro-intestinal disease, and for example with lymphoma may obviate the need for an exploratory surgery and biopsies. This is particularly useful for a disease that is managed primarily with systemic chemotherapy. In the evaluation of dogs with bladder tumors, ultrasonography is more sensitive for mass detection than either intravenous urography or double-contrast cystography. It is important to remember that ultrasonography is sensitive for lesion detection but it is not specific for disease etiology. There may be a high level of confidence as to the nature of the lesion but it is inappropriate to diagnose disease processes based on sonographic appearance. A definitive diagnosis requires cytologic and/or histopathologic confirmation.
Computed tomography (CT) has two main advantages over conventional radiography. Images are tomographic which refers to the "slices" obtained of the patient. Superimposition, which limits the utility of conventional radiography, is not considered to be a problem with CT. Also, because the images are computer generated the contrast between structures is significantly enhanced. Appropriate assessment of findings from CT imaging requires a basic knowledge of cross-sectional anatomy and necessitates a different way of thinking about images. CT imaging of brain and nasal tumors has attained widespread use, and radiologists as well as clinicians are familiar with interpretation. CT imaging is more expensive but it can provide a substantial amount of information and direct treatment planning. The use of intravenous contrast enhancement can markedly increase the ability to delineate the extent of local disease, e.g., vaccine-associated sarcomas in cats. CT's performed in the post-operative setting or after radiation therapy can be difficult to assess. A mass seen on a post-operative CT scan may represent scar tissue, necrotic tumor, or residual viable tumor. Neither radiography nor CT imaging can accurately predict which is present. Monitoring of the site may reveal persistent stable disease or slowing regressing disease, both potentially indicative of tumor control. A second surgery and/or surgical biopsy may be indicated.
Magnetic resonance imaging (MR) is used extensively in the diagnosis of brain tumors. It also provides more information on the extent of disease in soft tissue sarcomas in dogs and cats wherein CT imaging even with contrast may not adequately differentiate between normal soft tissues and tumor. MR is the dominant imaging modality for musculoskeletal tumors in humans because of the superior soft tissue definition as well as in evaluation of bone marrow. Another application of MR is in the imaging of thyroid tumors prior to surgery and/or local radiation therapy. It is possible to identify vasculature, the tumor and it's relationship to the surrounding tissues to better understand the likelihood of a successful outcome from surgical resection.
Once all information has been gathered as to the nature and extent of the local tumor as well as extent of regional and distant metastasis then a treatment plan(s) can be devised and discussed with the owner. It is also important to discuss the possibilities with the owner prior to an extended and potentially expensive diagnostic work up. If the outcome is likely to be the diagnosis of a primary tumor that the owner would not subsequently want to treat then the initial diagnostics can be more limited to what is absolutely necessary to provide a diagnosis. It is also critical to the ultimate success of therapy that where indicated all specialists contribute to and discuss the possible therapeutic options. Medical, radiation, as well as surgical oncologists must work as a team to increase the likelihood of a successful outcome. Pre-planning therapy is the key to success in cancer management.