Extremity Soft Tissue Sarcoma
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Direct answer
Any deep, enlarging, painless lump in a limb larger than 5 cm is a soft tissue sarcoma until imaging and biopsy prove otherwise — MRI of the part is the local staging study, and the biopsy itself must obey surgical discipline: a core needle biopsy (or planned incisional biopsy) placed so that the tract and scar are excised en bloc with the tumour at definitive surgery, performed at (or in consultation with) the centre that will do the resection. Definitive treatment is limb-sparing wide excision with a margin of 1–2 cm of normal tissue (or a reactive-zone-plus-barrier concept where anatomy dictates), combined with radiotherapy — preoperative (about 50 Gy, better long-term function but higher wound complications) or postoperative (60–66 Gy) — achieving local control above 90 per cent in modern series; amputation is reserved for tumours that cannot be excised with a margin while leaving a functional limb. The cardinal Indian exam scenario is the "whoops procedure" — a lump assumed to be a lipoma and shelled out, returning as sarcoma on histology; the answer is re-excision of the whole scar, tract and tumour bed with true margins.
What you must remember
- Diagnosis discipline: MRI with contrast defines size, compartment and neurovascular relations; core needle biopsy through a single tract (longitudinal on the limb, in line with the future incision) is standard; fine-needle cytology is inadequate for grading; never enucleate an undiagnosed deep lump.
- Grading: FNCLCC system scores tumour differentiation, mitotic count and necrosis into grades 1–3 — grade and size (and depth) drive staging and metastatic risk; the AJCC 8th edition T category for extremity sarcoma is T1 up to 5 cm and T2 over 5 cm (depth no longer defines T).
- Common adult histologies: undifferentiated pleomorphic sarcoma, liposarcoma (well-differentiated to dedifferentiated), leiomyosarcoma, myxofibrosarcoma in the elderly; synovial sarcoma in younger adults (t(X;18) SS18-SSX); in Indian paediatric practice, rhabdomyosarcoma dominates.
- The margin concept: excision encompasses the tumour with its pseudocapsule (which contains tumour satellites) plus a cuff of normal tissue — "shelling out" along the pseudocapsule leaves satellite nodules and guarantees local recurrence; a 1–2 cm margin or a fascial plane as barrier is the standard.
- Radiotherapy timing: preoperative 50 Gy with postoperative boost if margins are close (the Canadian NCIC trial showing comparable local control, smaller fields and better limb function, at the price of wound complications in about a third); postoperative 60–66 Gy after healing; brachytherapy and IMRT are techniques; sarcomas are classically radioresponsive-enough for local control without radical dose.
- Neoadjuvant chemotherapy: considered for high-grade, large (over 5 cm), deep tumours in fit patients (regimens like MAID), though its role in adult STS is less settled than in paediatric disease; isolated limb infusion with TNF and melphalan offers limb salvage for locally advanced disease in specialist centres.
- Nodal disease is rare (about 2–5 per cent) — epithelioid sarcoma, clear cell sarcoma, angiosarcoma and rhabdomyosarcoma are the exceptions that spread to nodes.
- Metastatic pattern: haematogenous to lung first — baseline chest CT and its inclusion in follow-up imaging; oligometastatic pulmonary metastasectomy in selected patients offers survival benefit.
- The whoops excision: re-image, stage, and re-excise scar and tract with a true wide margin (roughly a third to half harbour residual tumour); refer to a sarcoma centre, since unplanned excision followed by correct re-excision can still achieve good local control.
A worked example
A 48-year-old man notices a slowly enlarging 9 cm deep lump in his right thigh; a local surgeon excises it as a "lipoma" through a longitudinal incision, and histology returns high-grade myxofibrosarcoma with tumour at margins. Correct the pathway: MRI of the thigh with contrast to map residual disease and oedema tracks, chest CT to exclude lung metastases, and referral to the sarcoma multidisciplinary team. Plan: re-excision of the scar, biopsy tract and entire tumour bed with 1–2 cm margins — in the thigh this is achievable while sparing femoral vessels and sciatic nerve (compartmental resection only when the compartment is breached and non-essential) — followed by radiotherapy; many centres would give preoperative radiotherapy if residual tumour is bulky. Had he presented unoperated, the sequence would be: MRI, core biopsy at the treating centre, staging, then preoperative radiotherapy and wide excision (or surgery first with postoperative radiotherapy). Either way he enters surveillance — clinical examination plus imaging of the limb and chest at defined intervals for at least 5 years — because local recurrence and lung metastases remain possible. And if the tumour had encased femur, vessels and nerve with a frozen, bleeding limb? That is the rare modern indication for amputation after all limb-salvage options (including isolated limb infusion) are exhausted.
Where students slip
The first slip is the biopsy-free excision: answers must begin with MRI and planned core biopsy, because the "shelled-out lump" scenario is exactly how sarcomas are disseminated. The second is margin dogma — students recite "5 cm in all axes" from older texts; the contemporary answer is 1–2 cm or an intact fascial barrier, with radiotherapy complementing surgery. The third is forgetting lung staging — sarcoma metastases go to lung, so the baseline study is a chest CT, not a liver ultrasound.
Frequently asked questions
What imaging defines the local extent of an extremity soft tissue sarcoma?
Contrast-enhanced MRI of the entire compartment — size, depth, neurovascular relations and skip areas — with chest CT for haematogenous lung staging.
How is the "whoops" excision of a presumed lipoma that proves sarcoma managed?
Re-image, stage and re-excise the entire scar, tract and tumour bed with true wide margins at a sarcoma centre; residual tumour is found in a substantial proportion of such beds.
What margins and dose concepts apply in limb-sparing sarcoma surgery?
Wide excision with 1–2 cm of normal tissue or an intact fascial barrier, combined with radiotherapy — preoperative about 50 Gy or postoperative 60–66 Gy.
Which soft tissue sarcomas preferentially spread to lymph nodes?
Epithelioid sarcoma, clear cell sarcoma, angiosarcoma and rhabdomyosarcoma — most others metastasise haematogenously to lung.
What does the FNCLCC grade score?
Tumour differentiation, mitotic activity and necrosis, producing a three-tier grade that drives staging, prognosis and decisions on chemotherapy and radiotherapy.
When is amputation still indicated in extremity sarcoma?
When a wide margin cannot be achieved while preserving a functional limb — after exhausting limb-salvage surgery, radiotherapy and, in selected centres, isolated limb infusion.