Soft tissue tumours in children comprise of a group of tumours that develop in mesenchymal tissue. They have been divided in two groups- Rhabdomyosarcomas (RMS) and non-rhabdomyosarcomas (NRSTSs). About half of them are RMS presenting in less than 6 years of age while NRSTS comprise of a heterogenous groups including synovial sarcomas, Ewing’s Sarcoma, Nerve sheath tumours and others; they are seen in the older age group.
STS is seen in 6-8% of all cancers seen in childhood and most of them have sporadic occurrence. The syndromic/inherited risk is seen in – Li-Fraumeni syndrome, Familial adenomatous polyposis, RB1 gene changes, Neurofibromatosis Type 1.
They present as a painless lump in any of the soft tissue of the body. If not treated the size keeps on increasing and cause pressure on the other organs, vessels or nerves depending on the location of the tumour. Sometimes very large tumours increase in size and ulcerate or fungate. The most common sites are arms, legs and trunk.
The cancer cells spread locally into the surrounding soft tissue, to the draining lymph nodes and to other organs of the body through blood.
On clinical examination of the lump if tumour (cancer) is suspected a few tests are done before doing any intervention.
Magnetic resonance imaging (MRI) is done for assessing the local extent of the tumour especially in relation to nerves and vessels. The younger children require anaesthesia and it takes time to image the required region. Contrast-enhanced computed tomography (CECT) is preferred if the location of the tumour is in the chest or abdomen.
The biopsy is required once the presence of STS is confirmed. It is important to consult with the operating surgeon before the biopsy is planned. There should be adequate tissue for required microscopic examination, immunohistochemistry and molecular tests for diagnostic and prognostic evaluation. The type of biopsy depends on the size and extent of disease. The core needle biopsy is performed taking multiple cores of tissue and if it is located deep or at the difficult location the biopsy is done under image guidance. The excisional biopsy is complete removal lump with an adequate margin of normal tissue. It can be performed for small tumours provided if it is not affecting function or cosmesis.
Metastatic workup: Sentinel lymph node biopsy to see if the tumour cells have gone beyond the group of first draining lymph nodes. It is done during surgery using blue dye or a radiotracer. PET scan assesses the tumour spread to nodes and other parts of the body.
Staging and risk stratification
Once the diagnosis is confirmed the patients are risk-stratified based on the extent of resection, a grade of the tumour, size and presence or absence of metastasis into low, intermediate and high risk. This guides the treatment planning and outcome of the patients.
Surgery includes removal of the tumour with a surrounding rim of normal tissue. The removal of a tumour depends on location, closeness to vessels and nerves, the feasibility of getting clear margin and functional and cosmetical outcomes. Sometimes amputation is the only option. For large unresectable tumours at presentation, the surgery is performed after giving chemotherapy. The metastatic disease might require surgery or radiation later depending on the histology (type) of a tumour, response to chemotherapy and location of metastasis.
Chemotherapy includes various combination of cytotoxic drugs that are used to control cancer cells. It also helps in decreasing the size of the tumour and make surgery possible if one is not able to operate at the time of diagnosis. There are few soft tissue tumours (in NRSTS category) that do not respond to chemotherapy making treatment often challenging especially if surgery is also difficult.
Radiation therapy uses high energy rays delivered to the tumour site to destroy cancer cells. These rays can be delivered as external beam using machine which is outside body or brachytherapy where wires, needles or moulds are placed and radiation is delivered directly at the tumour site. The later has lesser side effects but it is not always feasible in all patients.
For a low-risk disease where the tumour is completely excised and has good biology, the outcomes are good. The outcomes in low, intermediate and high risk are around 95%, 80% and 36% respectively.