The Musculoskeletal Tumour Society staging system

The MSTS (Enneking) staging system for sarcomas is another exam classic.  This is a very straightforward system which allows the user to describe the extent of the tumour locally and systemically. Tumours are either low grade (Stage 1, <15% risk of metastasis), high grade (Stage 2, >15% risk of metastasis) or metastatic (Stage 3).

Intracompartmental tumours are classified as “A” and extracompartmental tumours as “B”.

For example, an osteosarcoma of the distal femur, which has an associated soft tissue mass but no detectable metastases would be staged as “2B” in this system.

Other systems include the AJCC system for staging.

Reference:

Enneking WF, Spanier SS, Goodman MA. Current concepts review. The surgical staging of musculoskeletal sarcoma. J Bone Joint Surg Am 1980;62(6):1027-30.

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The five presenting complaints of musculoskeletal tumours

According to Levesque et al in their excellent book “A clinical guide to Primary Bone Tumours”, the five ways in which patients with musculoskeletal tumours present are:

  1. A soft tissue mass
  2. A painless bony mass
  3. A bone tumour as an incidental finding
  4. A painful bone lesion
  5. A pathological fracture
The approach to each clinical scenario has a different emphasis.

Describing surgical margins

The description of surgical margins requires an understanding of the local behaviour of sarcomas. Classically, sarcomas grow centrifugally, and around the central tumour is a “reactive zone” comprising compressed normal tissues, inflammatory cells and small numbers of tumour cells. Tumours also tend to stay within osteofascial anatomical compartments. These concepts were popularised by Enneking, in the era before the widepsread availability of cross-sectional imaging.

The text-book answer is that surgical margins are described as follows:

  • Intralesional – when the resection passes through tumour
  • Marginal – when the resection passes through the reactive zone
  • Wide – when the resection passes through normal tissue
  • Radical – when the whole of the involved compartment is removed.

However, given that the majority of tumours are close to critical neurovascular structures for at least part of their circumference, most resections are technically marginal.  A more helpful description is often whether or not the margin is microscopically positive (tumour at or within 1mm of the resection margin) or microscopically negative.

The surgical margin achieved is the strongest predictor of the risk of local recurrence in several large series.

 

 

What is a tumour?

A growth or swelling, which enlarges by cellular proliferation more rapidly than surrounding normal tissue and continues to enlarge after the initiating stimuli cease. Usually lacks structural organization and functional coordination with normal tissues and serves no useful purpose to the host organism.