Much attention has been paid lately to the presence in cancers of bodies which by many are interpreted as minute animal parasites belonging to the protozoa, to the class of sporozoa^and to the genus coccidium. There are undoubtedly round or oval bodies which are present in some of the epithelial cells in almost all cancers. These are shown in Fig. 108. They present certain •colour reactions with staining agents, which show them to be different from the ordinary cell structure. They are present chiefly in the protoplasm of the cell, but have also been described in the nucleus. These parasites in the epithelial cells are supposed to stimulate the latter, and being animal cells they may enter into conjunction with the epithelial cells and induce the special action.
This view has been supported by the citation of certain facts connected with parasitic protozoa and their action. In the disease Coccidiosis (see under Animal Parasites) a parasitic protozoon grows in the epithelial cells of the hepatic ducts, and leads to a marked proliferation of epithelium, so that gland-like tissue is formed, in which new-formed connective tissue supports the growing epithelium. The parasite, the coccidium oviforme, in a case recorded by Gubler, produced in the human subject a number of tumours in the liver which were taken to be cancerous. Further, in Molluscum contagiosum (see under Diseases of the Skin), there is a great new-formation of epithelium, so that what is virtually an epithelial tumour is produced. In this case there grow in the epithelial cells bodies which are possibly parasitic protozoa (the so-called molloscum bodies). The contagious nature of the disease suggests a parasitic origin.
In the case of cancer a parasitic origin might explain the malignancy of the disease and its spreading character. When it once begins, a •cancer spreads by inducing the normal epithelium to take part, and the multiplication of a parasite might explain this. It would also explain the general malignancy should epithelium and parasite be transplanted together. On the other hand, there are features in cancer which are difficult to explain on the view of a parasitic origin. The local character of the primary tumour is one of these. In coccidiosis and molluscum contagiosum we have, as in diseases due to parasitic microbes, many lesions produced by the parasite, but in cancer a multiple origin is never seen, and even two primary tumours are rare. Again, cancer is a proper tissue growth, and in different forms of the disease the tissue produced shows great variety. This seems inconsistent with a parasitic origin, unless there be many different kinds of coccidia. On the whole, the presumption seems in favour of the parasitic origin, but there are many facts to be elucidated before it can be fully accepted.
Fig. 108. - From a section of a cancer showing the so-called cancer bodies. In addition to the nuclei, which are oval bodies of uniform size, there are round or oval bodies of various sizes generally more or less clear, except in the centre.
The literature of this subject is already very extensive. (See a list of 112 references by Stroebe, Centralbl. f. Allg. Path., 1894, p. 11.) Some of the principal papers are: Russell, Brit. Med. Jour., 1890, vol. ii.; Soudakewitch, Ann. de l'lnst. Pasteur, vol. v., 1892; Buffer and colleagues, Journal of Path., vol. i., 1892,. p. 189 (with history and literature); ibid., vol. i., 1893, p. 395; ibid., vol. ii., 1893, p. 3; Clarke, Cancer, Sarcoma, and other morbid growths, 1893; Pianese, Histol, and etiol. of Carcinoma (Trans.), 1896.
We have seen that cancer is characterized by the atypical growth of the epithelium. The growing epithelium sends out buds or offshoots which penetrate into the underlying or surrounding tissue. In this way a primary cancer does not usually grow into a considerable tumour, but rather insinuates itself amongst the tissues around. Hence we speak of Cancerous infiltration as characteristic of most tumours of this kind.
The question of the Inoculation of cancer is one which naturally suggests itself, and many experiments have been performed both on man and animals to determine the possibility of such inoculation. These experiments have not so far been conclusive. It is not uncommon, however, to find what may be called Auto-inoculation. Thus a cancer of the posterior wall of the urinary bladder will sometimes extend to a point on the anterior wall where the tumour comes in contact when the bladder is empty.
The growing cancerous processes frequently lead to much irritation in the connective tissue, so that we may have, in cancer of the lip, for instance, the extremities of the cancer cylinders buried in masses of round cells. Sometimes there is considerable cicatricial formation apparently induced by the insinuating cancerous processes. On the other hand, the tumour may lead to little irritation, and the cancer with its characteristic stroma may grow amongst the normal tissues, merely acting on them by pressure.
The effect on neighbouring structures is to cause atrophy of their proper elements by pressure, so that the cancer takes the place of the normal tissue.
If the cancer originates at a surface, or in its growth comes to present itself there, then its tissue, being less resistant than the normal structures, breaks down and we have ulcers following. Ulceration is generally present in cancers of the skin and mucous membranes, and in the later stages of glandular cancers.
Besides this local malignancy cancers frequently produce tumours at a distance. It is well known that the Secondary tumours mostly occur in the lymphatic glands.. This may be explained partly by the anatomical connection already mentioned, and partly also by the fact that the growing cancerous process extending in the direction of least resistance will readily pass into the spaces in the tissues which are the radicles of the lymphatic vessels.
It seems not improbable, on the other hand, that cancer has a special affinity for lymphatics. The author has observed, for example, in cases of secondary cancer of the lung, that although brought to the lung by the pulmonary artery, the cancerous growth has been chiefly in the lymphatic vessels to begin with. In one such case it was quite common to find, in the neighbourhood of the pulmonary artery, the lymphatic spaces in the sheath filled out with cancerous masses. (See under Affections of the Lungs).
The cancer forms a true new-formation in the lymphatic glands. The tumour-formation mostly begins at the peripheral parts of the gland, these being the parts to which the afferent vessels are distributed and here the characteristic epithelial structure is developed. It is sometimes very striking in the earliest periods of infection of the glands to find layers of cancerous tissue at the periphery enclosing the follicles of lymphatic tissue. The latter tissue undergoes atrophy, so that we may have only here and there groups of round cells representing the proper lymphatic gland tissue in the midst of cancerous' tissue. Finally all trace of the normal tissue disappears.
It is an important practical question whether the enlargement of lymphatic glands in connection with cancers is always a true secondary infection. There is no doubt that, just as in the primary tumour, the cancerous growth is often associated with irritation, sometimes leading to cicatricial conditions of the gland (especially in colloid cancer), but in that case there is the cancerous infection as well. In the case of ulcerating cancers, on the other hand, irritating products of decomposition may be carried to the glands, and give rise to a simple non-cancerous enlargement. Hence enlargement of glands is of less significance in ulcerating cancers than in those which are not ulcerated, but in all cases enlargement of the glands is to be looked on with suspicion.