The Spindle-Celled Sarcoma (Fig. 98) is also called the fibrosarcoma, and corresponds with Paget's class of recurrent fibroids, and Lebert's group of fibro-plastic tumours. The cells are spindle-shaped, like those in the deeper layers of a granulating wound, and there is comparatively little intercellular substance, the tumour being mainly composed of masses of spindle-cells. There is always, however, a certain amount of intercellular substance, which consists of fibresgenerally of some density. The cells are arranged in bundles,, which to a certain extent interlace like the bundles of fibre-cells in the myoma. There are great varieties in the size of the cells, some tumours being composed of very small cells, and these are usually soft, while at the opposite extreme are cases where the spindles are gigantic. When viewed in mass the individual spindles may not be apparent, but they are usually easily isolated, unlike the fibre-cells of the myoma. These tumours, except the small-celled forms, are usually firmer than the round-celled sarcomas, and. may even approach the fibroma in hardness. Many of them show a tendency to more complete organization into fibrous tissue, cartilage, or bone.

Fig. 97. - Round-celled sarcoma infiltrating adipose tissue.

Fig. 98. - Large colls from a spindle-celled sarcoma. X 300.

The spindle-celled sarcoma occurs frequently in the periosteum, and in that case is firmly attached to the bone (see Fig. 99). It is also-met with in or under the skin (see Fig. 100), in muscles, in the testicle, etc. It is a frequent tumour in the mamma, and here it not infrequently forms the adenoid sarcoma and the cystic sarcoma.

The spindle celled sarcoma is usually a distinctly defined tumour, but often, as in the case of the periosteal form, its boundaries are not defined, and it advances by incorporating neighbouring structures. (See Fig. 99.) Although prone to return after removal, it has less tendency than the round-celled form to give rise to secondary tumours by metastasis.