What Is Tumour Staging?

The stage of a tumour is defined in simple terms as the extent of the neoplastic disease. It is an expression of both the tumour volume and the degree of tumour spread, both locally and to other distant sites. Tumour stage is of great importance in determining therapeutic options and prognosis, two concepts which are inextricably linked as each more or less defines the other. Strictly speaking we should differentiate clinical stage from pathological stage. Clinical stage classically summarises the information from non-invasive procedures while pathological stage determination requires information from a pathologist's inspection of excised tissue; the latter provides data of higher quality but requires more invasive testing.

There are recognised schemes for defining tumour stage; the most widely used in medical and veterinary oncology are the Union Internationale Contre le Cancer (UICC) (human) and World Health Organization (WHO) (veterinary) Tumour Node Metastasis (TNM) classification schemes. Within these schemes there are separate classifications according to tumour types and anatomical locations. In human medical oncology, classifications are derived from analysis of evidence from large-case studies. In the veterinary world, the WHO TNM classification schemes are largely extrapolated from their human counterparts though other clinical stage schemes are increasingly being presented which have been derived specifically from the analysis of appropriate cases.

Definition of tumour stage evaluation procedures as appropriate or inappropriate for any given tumour requires knowledge of the typical behaviour of that tumour type. Often clinical stage determination involves assessment of regional lymph nodes and thoracic radiography. Other specific evaluations are appropriate in particular contexts.

Tumour staging provides a shorthand notation of the gravity of a neoplastic problem. While it is not pretended that it can replace a detailed clinical assessment, it provides a useful means of communication between practitioners when discussing affected cases.

What Can Be Achieved by Tumour Staging?

It would be accurate to say that tumour stage is the single most significant determinant of prognosis in cancer. By defining the extent and invasiveness of a tumour, we can predict whether certain treatments are applicable or not. For example, in patients with mammary masses, obtaining thoracic radiographs prior to surgery allows identification of patients with gross pulmonary metastases, a finding that would likely indicate that surgical management was inappropriate.

Knowledge of the prognostic implications of particular tumour stage determinations allows the clinician to employ directed investigations so that specific prognostic questions can be asked. For example, mast cell tumours preferentially spread through the lymphatic system; cytological evaluations of the draining lymph node can give a strong indicator of the presence or absence of metastatic spread steering a decision regarding local therapy.

There are correlations between the extent of neoplastic disease and the incidence of other apparently unrelated disorders. For instance, coagulopathies are recognised in association with disseminated neoplasia. Therefore, aside from the straightforward implications of reduced life expectancy with more advanced disease, the risks of significant perioperative complications, including death from coagulopathy, are higher with more advanced neoplasia.

Tumour stage determination therefore:

 Guides therapeutic decision making

 Reduces perioperative morbidity/mortality

What Cannot be Achieved by Tumour Staging?

Owners sometimes fail to comprehend that clinical stage evaluations provide a summary of the state of that patient's neoplasia solely at the time of performing the test. A 'clear' thoracic radiograph today is of no predictive value in 6 months' time. If further therapeutic decisions need to be made at a later date, a rational assessment of the clinical stage of the tumour at that time is indicated.

Clinical stage determination should be used to assess a patient's extent of disease and while a negative finding can provide peace of mind, it is important to emphasise that there is no overt medical benefit in having the procedure performed. On an individual patient basis, if the findings of clinical stage determinations are not going to influence treatment decision making, these investigations are hard to justify.

Are All Tumours Staged in the Same Way?

It is not appropriate to perform the same clinical stage determination evaluations for all patients with neoplastic disease. The decision to undertake clinical stage determinations is made on the basis of the practitioner's index of suspicion that the test will influence subsequent decision-making. Factors that will define the evaluations performed include the tumour type, tumour grade and accompanying clinical signs. For example, most grade 1 cutaneous mast cell tumours in dogs are solitary lesions with a negligible risk of metastasis. Only cases with clinical signs consistent with systemic disease might warrant further evaluations. By contrast, grade 3 cutaneous mast cell tumours are frequently associated with metastasis and local surgery would need to be radical to afford the patient a chance of local cure. While it would be unrewarding to undertake clinical stage determinations in a patient with low-grade disease, it would be deeply unwise to perform radical surgery without knowledge of the full extent of the patient's neoplastic disease in a high-grade tumour.

Rational Tumour Staging

All procedures performed on a patient carry certain costs. The joy of veterinary practice, particularly first-opinion veterinary practice, is that decisions need to be made not only on clinical grounds but also on the basis of the probability that the result of said decision will be beneficial in the further management of a case. Bone marrow aspiration can be performed for the determination of stage in lymphoma. Rationally, if the patient has a normal haemogram, the probability of bone marrow involvement is low and it is unlikely therefore that such a procedure would influence treatment decision making.

In order to be able to make rational decisions about which clinical stage determinations are indicated, the practitioner needs to have a strong working knowledge of the clinical behaviour of the different tumour types.

How to Avoid Fouling Up

The role of the veterinary practitioner is to make an educated assessment of their patient's clinical status and to seek to obtain the best outcome for patient and owner within the parameters that are defined by the patient's clinical condition and the limitations imposed by the owner. Inevitably decisions need to be made that will impose some cost, whether in medical, temporal or financial terms. As well as making the best decisions for all parties, the veterinary surgeon also needs to be confident that their decision making carries the least chance of resulting in a catastrophic error. The solution to this is to proceed in an orderly fashion.

1.  Make your diagnosis. This should be done by the least invasive means likely to obtain a definitive result such as fine needle aspirate or incisional biopsy.

2.  Identify parameters that will define your treatment goals. These are both tumour parameters and owner parameters. Not all tumours can be managed; not all owners will want to manage their pet's tumour.

3.  Define the problems that need to be resolved. These include actual clinical problems, such as the presence of a tumour and the currently unknown clinical stage of the disease. There are problems of perception too, such as owners' preconceptions about chemotherapy. There are potential problems, for instance functional consequences of radical surgery. Identifying these problems allows the veterinary surgeon to define which therapeutic options are available and which are not. (There is little or no value in defining the clinical stage of a tumour when the only therapeutic option that will be accepted is euthanasia).

4.  Define clinical stage in a rational order. Prior to planning definitive therapy we need to know about the degree of invasiveness of the primary tumour and the status of distant spread. We also need to know the potential costs of these investigations including medical risks associated with, for instance, sedation or anaesthesia, or entry into body cavities and biopsy.

So Why Bother with Tumour Staging?

There has to be a problem to solve for you to need clinical stage information to reach the solution so clinical stage evaluations need to be justified if they are to be undertaken. All procedures performed carry a cost, whether that is medical, financial or a time cost for the owners; the cost of clinical stage determinations must not prohibit definitive therapy. All diagnostic tests carry a certain risk of yielding an incorrect result. There are few things that aggravate owners more than only growing to understand that diagnostic tests have limitations once the limitation in question has proved itself following supposed definitive therapy.

We need to know tumour stage in order to define prognosis. We need to define prognosis in order to make rational treatment decisions. Tumour staging is therefore a critical element of the management of oncology cases. In order to perform the best service for our clients and patients, we need a good working knowledge of different tumour types and grades in order to make rational tumour staging decisions. Rational tumour staging allows us to make best use of our clients' resources and most importantly enables us to minimise unnecessary morbidity in our patients.

References

General Tumour Stage Information

1.  Owen LN. TNM Classification of tumours in domestic animals. Geneva, World Health Organization, 1980.

2.  Sobin LH, Wittekind CH, Henson DE. How to use the TNM classification. In: TNM Online. 2007 John Wiley and Sons, New York. http://www.uicc.org/index.php?option=com_content&task=view&id=14296&Itemid=221 (Accessed 24/08/07)

Derivation of a Clinical Stage Scheme

1.  Polton GA, Brearley MJ. Clinical stage, therapy and prognosis in canine anal sac gland carcinoma. Journal of Veterinary Internal Medicine 2007; 21: 274-280.