Page 876 - Textbook of Pathology, 6th Edition

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Chapter 29 Soft Tissue Tumours
Chapter 29

GENERAL FEATURES ETIOLOGY AND PATHOGENESIS. Etiology of soft tissue
tumours remains largely unknown; however, a few common
INTRODUCTION. For the purpose of classification of this features in etiology and pathogenesis apply to many soft
group of tumours, the WHO has defined soft tissues as all tissue tumours:
“non-epithelial extra-skeletal tissues of the body except the 1. Frequently there is history of antecedent trauma which may
reticuloendothelial system, the glia and the supporting bring the tumour to attention of the patient.
tissues of specific organs and viscera”. Thus, soft tissues 2. Molecular and cytogenetic studies in many soft tissue
included for the purpose of categorisation of their tumours tumours reveal chromosomal abnormalities and mutations in
are: fibrous tissue, adipose tissue, muscle tissue, synovial genes which can be used as a marker for diagnosis and
tissue, blood vessels and neuroectodermal tissues of the histogenesis e.g. translocations, various fusion genes etc.
peripheral and autonomic nervous system. The lesions of 3. Most of the soft tissue tumours occur sporadically; however
these tissues are embryologically derived from mesoderm, there are a few examples which are components of genetic
except those of peripheral nerve which are derived from ecto- syndromes e.g. neurofibromatosis type 1, Li-Fraumeni
derm. Tumours of smooth muscle tissue, blood vessels and syndrome, Osler-Weber-Rendu syndrome etc.
nerves are described elsewhere in the book, while tumours CLASSIFICATION. Currently, the WHO classification
and tumour-like lesions composed of other soft tissues are divides all soft tissue tumours into following 4 categories:
discussed in this chapter.
Benign soft tissue tumours are about 100 times more Benign: These soft tissue tumours generally do not recur and
common than sarcomas. Sarcomas rarely arise from malig- are cured by complete excision. Common example is lipoma.
SECTION III
nant transformation of a pre-existing benign tumour. Instead, Intermediate, locally aggressive: These tumours are locally
sarcomas originate from the primitive mesenchymal cells destructive, infiltrative and often recur but do not
having the capacity to differentiate along different cell path- metastasise. Such tumours are generally treated by wide
ways. As discussed in Chapter 8, soft tissue sarcomas excision; for example desmoid tumour.
metastasise most frequently by the haematogenous route and Intermediate, rarely metstasising: This category of tumours
disseminate commonly to the lungs, liver, bone and brain. are also locally destructive, infiltrative and recurrent but in
Lymph node metastases are often late and are associated with addition about 2% cases may have clinical metastasis which
widespread dissemination of the tumour. Histologic differen- may not be predicted by morphology. Common example in
tiation and grading of soft tissue sarcomas are important this category is dermtofibrosarcoma protuberans.
because of varying clinical behaviour, prognosis and Malignant: Tumours in this category are clearly malignant—
response to therapy. they are locally destructive, infiltrative and metastasise in a
Systemic Pathology
Majority of soft tissue tumours have following important
general features: high percent of cases. The metastatic rate in low-grade
sarcomas is about 2-10% and in high-grade sarcomas is
Superficially-located tumours tend to be benign while 20-100%.
deep-seated lesions are more likely to be malignant.
Large-sized tumours are generally more malignant than DIAGNOSTIC CRITERIA. Accurate pathological diagnosis
small ones. of soft tissue tumours is based on histogenesis which is
Rapidly-growing tumours often behave as malignant important for determining the prognosis and can be made
tumours than those that develop slowly. by the following plan:
Malignant tumours have frequently increased vascularity 1. Cell patterns: Several morphological patterns in which
while benign tumours are selectively avascular. tumour cells are arranged are peculiar in different tumours
Although soft tissue tumours may arise anywhere in the e.g.
body but in general more common locations are: lower i) Smooth muscle tumours: interlacing fascicles of pink staining
extremity (40%), upper extremity (20%), trunk and tumour cells.
retroperitoneum (30%) and head and neck (10%). ii) Fibrohistiocytic tumours: characteristically have storiform
Generally, males are affected more commonly than pattern in which spindle tumour cells radiate from the centre
females. in a spoke-wheel manner.
Approximately 15% of soft tissue tumours occur in iii) Herringbone pattern: is seen in fibrosarcoma in which
children and include some specific examples of soft tissue the tumour cells are arranged like the vertebral column of
sarcomas e.g. rhabdomyosarcoma, synovial sarcoma. seafish.