SURGICAL MARGINS

The key to successful surgical cancer management is very much dependent, in the majority of cases, on obtaining margins of normal tissue in addition to the main tumour mass. Even using this approach will not guarantee the complete removal of the tumour as there are often tumour cells that infiltrate the surrounding normal tissue in the form of ‘satellite’ or ‘skip’ metastasis (Fig. 2.1). Therefore in most circumstances there is a greater likelihood of complete local excision when wider margins are taken. The exact distance recommended depends on the tumour type, biological behaviour and anatomical location. For example with low- or intermediate-grade mast cell tumours a margin of 2 cm laterally is recommended and results in the complete excision of the majority of tumours. Deep margins must not be disregarded. However, often tumours lie over naturally resistant anatomical barriers such as fascia, ligaments and tendons which are resistant to tumour spread and therefore if a fascial plane is included in the deep margin this would normally be sufficient as an adequate surgical margin.

Figure 2.1 This diagram illustrates typical tumour anatomy of a soft-tissue sarcoma and demonstrates the presence of metastases outside the main tumour mass

There are four basic types of tumour resection depending upon the location of the surgical margin:

SURGICAL TECHNIQUES

The first attempt at complete excision will always give the best results with locally aggressive and/or malignant tumours. If an excisional biopsy has been previously performed with tumours such as soft tissue sarcomas then the chances of complete excision and therefore a potential cure are reduced. This is because disruption to the tumour from the first surgery can result in tumour seeding to surrounding tissues. Furthermore, disturbance of normal tumour margins can make identification of ‘normal’ versus ‘abnormal’ tissue difficult and also there will be less available local skin for adequate closure. For these reasons a second surgery normally requires even greater margins of excision compared with the first (Fig. 2.2). The exception to this rule is when the tumour type will not affect future treatment options (e.g. mammary tumours, single pulmonary and splenic masses) and in these situations, excisional biopsy is acceptable.

Figure 2.2 This dog has had recurrence of a mast cell tumour following excisional biopsy of the original tumour with incomplete margins (arrow indicates previous scar) on the lateral thoracic wall. The second surgery will be made difficult as now both the gross recurrence and previous scar will have to be included in the second excision

Known malignant tumours should be removed with an adequate margin of normal tissue. Recommendations are that locally aggressive tumours be removed with a minimum of 2 cm margins in the lateral planes and one fascial plane in the deep margin. It is not enough to just ‘shell’ out the tumour and then go back and remove further tissue as this may cause seeding and lead to recurrence. Attempts must be made to avoid disruption to the tumour and perform the excision by cutting through normal, disease-free tissue only (Figs 2.3, 2.4).

Figure 2.3 A mast cell tumour (location shown by the red arrow) previously diagnosed on aspirate with 2-cm margins marked out with a sterile marker pen

Figure 2.4 After excision with 2-cm minimum lateral margins and including the underlying fascial plane. Histopathology confirmed an intermediate-grade mast cell tumour with complete margins of excision

Tumours should always be handled carefully and if possible other means of tumour retraction other than using the hand should be used. This can be in the form of stay sutures, Allis tissue forceps or laparotomy sponges (Fig. 2.5). This will help to avoid tumour cell seeding into local, surrounding tissues. Lavage of the excision site with sterile physiological saline before closure may also be utilized to reduce the number of tumour cells remaining in the wound.

Figure 2.5 This is a case of a mast cell tumour excision demonstrating the use of Allis tissue forceps for tumour handling during dissection

Tumour surgery can be considered as ‘contaminated’ so recommended surgical procedures to avoid the risk of tumour seeding or spread include:

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