MEDICUS MARCH 2016

C L I N I C A L E D G E

Soft Tissue Tumours A Pathologist’s Perspective

Dr Daniel Wong Consultant Pathologist, Anatomical Pathology PathWest Laboratory Medicine, QEII Medical Centre

Despite the present attention given

S oft tissue tumours arise from non-epithelial extraskeletal tissues of the body, including muscle, fat, fibrous tissue, blood vessels and by convention, peripheral nerves. The overall incidence is not known as many benign tumours such as small lipomas never come to clinical attention. However, the Australian Cancer Council estimates that approximately 1,500 new cases of malignant soft tissue tumours (i.e. sarcomas) are diagnosed every year in Australia. Although rare compared to other adult malignancies, sarcomas account for 20 per cent of cancers in children and 10 per cent in young adults, leading to a significant burden of disease in terms of disability- adjusted life years. As sarcomas are rare and present with non-specific symptoms, patients often face delays and errors in diagnosis and management which contribute to morbidity, such as preventable amputations, as well as mortality. Accurate and timely diagnosis is best achieved in the context of a sarcoma multidisciplinary team, which includes Soft Tissue Surgeons, subspecialty Radiologists, Pathologists, Medical Oncologists, Radiation Oncologists as well as allied health staff. Most lesions can be accurately classified with a core biopsy. Preferably,

to modern molecular methods, histology remains

this should be performed by a Musculoskeletal Radiologist giving due consideration to factors such as a core tract, which is excisable at definitive resection and targeting areas of interest in heterogeneous lesions to maximise the likelihood of a successful diagnosis. Pathological assessment forms the cornerstone of diagnosis and is presently based on the 2013 World Health Organisation (WHO) Classification, which recognises over 140 separate soft tissue tumours and many more variants. In practice, allocation of lesions to either a benign, borderline or malignant category is usually suffice to guide subsequent management. The borderline category includes non-metastasising tumours with a significant risk of local recurrence as well as rarely metastasising tumours. Integral to the pathological assessment of sarcomas is grading, the most commonly used criteria being the French Federation of Cancer Centers Sarcoma Group (FNCLCC) system which assigns a grade from one to three based on the degree of differentiation, mitotic count and the presence of necrosis. In general, benign tumours are marginally excised and borderline tumours and sarcomas are widely excised. Neoadjuvant radiotherapy is

the fundamental basis of diagnosis with other techniques providing a supportive role only

considered for high-grade sarcomas whilst there is evidence to support the efficacy of chemotherapy in certain sarcomas such as rhabdomyosarcoma, Ewing sarcoma and synovial sarcoma. Pathological assessment of soft tissue tumours is unique in that final diagnosis often relies on the integration of histological features with various ancillary studies. Many lesions demonstrate cytogenetic abnormalities including gene translocations and amplification which can be detected using molecular techniques such as fluorescence in-situ hybridisation (FISH) and polymerase chain reaction (PCR). Electron microscopy still has a role in some cases to help identify the line of differentiation. However, it is important to emphasise that despite the present attention given to modern molecular methods, histology remains the fundamental basis of diagnosis with other techniques providing a supportive role only. Interpretation of molecular results in isolation is fraught with

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