Introduction

Tumour staging is a way of defining the extent of the tumour. Clinical staging describes the primary tumour, lymph node involvement and whether there are distant metastases. This is abbreviated to T (primary tumour), N (lymph node), M (metastases). This system allows for the most appropriate treatment to be determined and to provide advice on prognosis for the patient.

Clinical Staging

Tumour

The primary tumour is assessed for:

 Tumour type

 Size of the mass

 Degree of infiltration and invasiveness: how mobile is the mass, ulceration

This can be assessed with palpation and other imaging techniques. Cytology is useful in determining the type of tumour. However, not all tumours exfoliate well and a non-representative sample may be obtained. The grade of the tumour may also not be determined through cytology. This may be important to predict the likelihood of further spread.

Node

The local and regional lymph nodes are assessed for:

 Size

 Mobility

 Neoplastic cell infiltration

Size and mobility are assessed by palpation and with imaging. Fine needle aspirates (cytology) should be performed on all local lymph nodes. This can reveal whether there has been metastatic spread. If the primary tumour is inflamed the local lymph node may be reactive and this can be determined by cytology.

Metastasis

Tumours can spread to many areas of the body. Certain tumours have a predilection for different sites. The most common sites for spread are the lungs. Other sites include internal organs: liver, spleen, brain, bones and skin.

Radiographs and ultrasonography are used to determine whether there has been distant spread. However, imaging is not sensitive in identifying micrometastases. Often on imaging, nodules can be seen within the liver and spleen and cannot be differentiated from normal age-related change (hyperplastic nodules). Cytology has an important role to play. Ultrasound can be used to guide sample taking from these nodules and determine whether neoplastic cells are present.

The Role of Cytology

Cytology is the microscopic study of cells. Cytology or histopathology can be used to determine the type of tumour present. Samples can be obtained by fine needle aspirates, scrapes and impression smears from the primary mass, lymph nodes and suspicious nodules within organs.

The advantages of using cytology over histopathology are:

 Ease of sample collection. For a peripheral primary tumour and local lymph node sedation is not always necessary. Internal organs often only require the patient to be sedated.

 Less expensive: does not require a general anaesthetic or surgery.

 Less morbidity: unnecessary surgery can be avoided.

 Faster results: can be processed within a day.

The disadvantages of using cytology rather than histopathology are:

 Unrepresentative sample obtained: some tumours do not exfoliate very well, e.g., fibrosarcomas or the wrong area may be sampled in a lymph node.

 Cannot examine tissue architecture and whether blood and lymph vessels are invaded.

 Cannot determine grade of tumour which could give more information about behaviour of the tumour and prognosis.

Summary

Cytology is a cheap and relatively fast way of making a diagnosis and assessing whether there has been further spread of a tumour. This aids in treatment planning and advising owners on prognosis.

References

1.  Dobson JM. TNM Classification and clinical staging. In: Dobson, JM; Lascelles BDX. eds. BSAVA manual of canine and feline oncology (second edition). Gloucester: BSAVA, 2003; 18-20.

2.  Ogilvie G, Moore A. Biopsy. In: Ogilvie, G; Moore, A. eds. The veterinary cancer patient: a practice manual. New Jersey: Veterinary Learning Systems, 1996; 37-51.

3.  Thrall MA. Diagnostic cytology in clinical oncology. In: Withrow and MacEwens's small animal clinical oncology. Canada: Saunders Elsevier, 2001; 112-133.