Soft tissue sarcomas for trauma and orthopaedic exam candidates

Abstract

Soft tissue sarcomas (STS) represent a diverse group of malignant tumours for which surgery is the cornerstone of curative treatment. All STS patients should be managed by a specialized sarcoma multidisciplinary team (MDT). For non-metastatic STS, the surgical aim of treatment is the wide excision of the tumour. Amputations are infrequently employed as a first-line treatment, although may be required in complex or recurrent cases. Wound complications following STS surgery are not uncommon, and reconstructive surgery is key to promote healing. Radiotherapy may be utilized for large, high-grade STS, or those close to essential anatomical structures that necessitate a marginal resection. This radiotherapy may be delivered pre- (neoadjuvant) or post- (adjuvant) operatively, with the aim of reducing local recurrence rates. Systemic treatments such as chemotherapy are generally not utilized for localized STS, other than for a few, specific subtypes. In metastatic patients, systemic treatment may be employed with palliative intent. The management of localized STS recurrence follows the same principles as those of primary disease, with emphasis placed on re-staging all patients to rule out metastatic disease. Long-term patient follow-up is crucial to detect disease recurrence (local or systemic) and any significant treatment-related complications.

Introduction

Soft tissue sarcomas (STS) are a group of rare, heterogeneous malignant tumours that originate from mesenchymal tissue. The World Health Organization (WHO) has classified over 70 different STS sub-types, defined primarily by their tissue of origin. They may occur at any anatomical location, but most commonly arise in the extremities, followed by the trunk. The majority of cases arise beneath the deep fascia, with an average size at diagnosis 9–11 cm. Detailed guidelines for the management of STS are available from a variety of sources including the British Sarcoma Group and the UK National Institute for Health and Care Excellence (NICE). ^, Given the rarity and complexity of STS, it is essential that patients are managed by a specialist sarcoma multidisciplinary team (MDT). The core members of this team should include a specialist sarcoma surgeon, radiologist, pathologist, medical oncologist and/or clinical oncologist, clinical nurse specialist and a palliative care specialist.

Diagnosis

The accurate assessment of all potential STS cases prior to treatment is essential in order to avoid mistreatment. The unplanned excision of an STS should be avoided at all costs. A detailed history and examination should be carried out, with emphasis placed on tumour size, growth, pain, duration of symptoms and past medical history.

Imaging

All patients must undergo appropriate imaging which should include an ultrasound (US) and magnetic resonance imaging (MRI) with or without plain radiographs.

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US is an extremely useful triage tool to rule out other common pathologies presenting as a soft tissue lump. These include a lipoma, sebaceous cyst or soft tissue arterio-venous malformation. US is non-invasive, cheap and readily available, although is highly user-dependent.
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MRI provides the most accurate information for deep, large soft tissue tumours (see Figure 1 ). This ability to characterize a tumour and its adjacent neurovascular structures make it the gold standard for surgical planning. In cases where MRI is contraindicated (severe claustrophobia, implantable defibrillators/cerebral metalwork) a computer tomography (CT) with contrast may be utilized.

Figure 1

Selected MRI images of a superficial high-grade sarcoma involving the lateral aspect of the left hip. ( a , b ) Coronal T2 and T1 weighted images respectively. ( c , d ) Axial T2 and T1 weighted images. The T2 weighted image highlight the tumour’s heterogeneity and surrounding oedema concerning for an aggressive lesion.
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Plain radiographs’ role in STS assessment is generally limited, although they can be used to identify any nearby bone involvement, assess fracture risk, or detect calcification within a tumour.

Biopsy

A biopsy should be obtained for all lesions that remain indeterminate after appropriate imaging. Image-guided core needle biopsy is the standard method utilized. Incisional and/or excisional biopsies may be required if image-guided techniques are either deemed not safe (due to large, nearby neurovascular structures) or fail to secure enough tissue for analysis. The principles of biopsy should be adopted in all cases. These include the use of a longitudinal incision that can be excised at the time of a patient’s definite resection, contamination of only one anatomic compartment, meticulous haemostasis, and positioning of a drain (if required) in line with the skin incision. Fine needle aspiration (FNA) has no role in STS biopsy due to high false-negative results, and the inadequacy of FNA samples for the cytogenetic, molecular or immunohistochemical studies often needed for STS diagnosis.

Staging

Approximately 10% of STS patients have detectable metastases at the time of presentation with the majority of cases metastasizing to the lungs. Considering this, almost all patients with confirmed STS should undergo a chest CT before treatment, with a plain chest radiograph reserved for particularly frail, elderly patients. While isolated visceral metastases are rare, a CT of the abdomen and pelvis should also be performed in high risk tumours. Depending on histological subtype, other staging imaging may be advised. In cases of myxoid liposarcoma soft-tissue metastases are common, and so whole-body MRI should be strongly considered. In alveolar soft part and clear cell sarcoma a relatively high incidence of brain metastases is seen, supporting the use of brain CT or MRI. Positron emission tomography (PET-CT) scanning may also be considered in patients in whom particularly radical surgery is planned, when traditional staging reveal no evidence of metastases.

Limb-sparing sarcoma surgery

Surgery is the cornerstone of the curative treatment of localized STS (see Figure 2 ). Definitive STS resections should be performed at a UK National Institute for Health and Care Excellence (NICE) designated STS treatment centre by a specialist sarcoma surgeon. An STS should be removed in a single specimen, with a rim of normal tissue surrounding it. This is termed a wide local excision, that achieves a ‘negative’ (microscopically tumour-free) margin. In the majority of cases this can be achieved with limb-sparing surgery. If not, an amputation should be considered.

Surgical margins

Many studies have concluded that a ‘negative’ surgical margin is key to avoid local recurrence. ^, The exact amount of acceptable uninvolved tissue surrounding a resected STS is debated, with 1 cm of tissue being accepted historically. More recent evidence has suggested that smaller surgical margins are acceptable, and that even microscopically positive margins are appropriate if perioperative radiotherapy is used (see below for more detail). It is also clear that the tissue composition of a margin impacts outcome, with lower rates of local recurrence seen when fascia or periosteum is present, compared to muscle or areolar tissue.

Histological surgical margins

Historically Enneking et al. described a model for sarcoma resections in 1981 based on the anatomical and pathological features of sarcoma growth (see Figure 3 ). This model took account of the potential presence of microscopic tumour in a malignant tumour’s reactive zone (termed its ‘pseudocapsule’), and the possibility of tumour ‘microsatellites’ within adjacent normal tissues. The group classified tumour resections into four categories:

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Intralesional: resected tumour is breached macroscopically
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Marginal: a tumour’s pseudocapsule forms at least part of a resected tumour specimen’s margin
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Wide: non-reactive, normal tissue is found at the entire periphery of the resected specimen
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Radical: all tissue within the anatomical compartment containing the tumour is removed.