The cancerous infection may for a time remain confined to the primary seat and the lymphatic glands, but it is liable to extend further and become generalized. This occurs by the material of infection reaching the blood, and being carried by it to distant situations. For the most part this metastasis by the blood only occurs after the lymphatic glands have been for some time affected, and the infection takes place from the lymphatic glands. It may be that in some cases there is a direct extension from the primary tumour to the blood.
The infection may occur from the lymphatic glands after the complete removal of the primary tumour. This had happened in a case observed by the author in which, after excision of an epithelioma of the vulva, the lymphatic glands in the groin, having been affected, gave rise to multiple secondary tumours in various organs.
Having reached the blood the infection is carried throughout the body, and Grafts are implanted in various organs. If the lymphatic glands be in communication with the systemic veins, then the infection will be carried to the lungs and on into the systemic arteries, but if they be in connection with the portal circulation, then the liver will be the organ to which they will be conveyed. This secondary (or tertiary) infection of distant organs occurs by Embolism, portions of cancerous tissue, perhaps only young cells, being planted in various organs, and tumours are produced having all the characteristic structure of cancer.
The metastatic growth does not occur so readily in some organs as in others. It is commonly said that the situations in which primary cancer occurs are comparatively seldom affected secondarily. Thus the mamma, uterus, and stomach are rarely the seat of secondary tumours. On the other hand, the liver, lungs, kidneys, heart, skin, and bones are frequently the seat of such tumours. In some forms of cancer secondary tumours are peculiarly liable to form in the Bone-marrow in various parts of the skeleton. The brain is comparatively seldom affected either with primary or secondary cancers. Perhaps of all organs the liver is most liable to secondary development of cancer. As it receives blood from the systemic as well as from the portal circulation it may be infected, whatever the seat of the primary tumour.
There are some apparent anomalies in the distribution of cancers to liver and lungs respectively. Thus a cancer of the lower end of the esophagus will often give rise to secondary tumours in the liver, while cancer of the stomach may give rise to tumours in the lungs. The author believes that this depends chiefly on the relations of the lymphatic glands from which the infection of the blood occurs. In a case of cancer of the oesophagus observed by the author, he found that extension had occurred first to the lymphatic glands beneath the diaphragm and thence to the liver. On the other hand, in a case in which primary cancer of the stomach gave rise to tumours in the lungs, he found that the pre-vertebral glands were affected and that extension had occurred (as evidenced by the occurrence of thrombi) to the vena cava.
The secondary tumours are often more favourably situated for growth than the primary one. They may be better supplied with blood and less exposed to mechanical or other interference. Hence they often grow to much larger size than the primary one, and may show the structure more fully developed. Thus the liver is often the seat of bulky tumours, while the primary tumour is quite insignificant.
In their structure the secondary tumours imitate the primary one even in the finer details. This applies not only to the shape and size of. the epithelial cells, but to the abundance and arrangement of the stroma, and even of the vessels in the stroma. If the stroma be abundant and fibrous in the primary tumour, it will show, at least, a tendency in the same direction in the secondary ones, although time may have failed to allow of the full manifestation of this.
This imitation of the primary growth produces very remarkable results, when one sees, for instance, a tissue consisting of gland-like spaces, lined with cylindrical cells, growing abundantly in the liver, or lung, or brain. A striking illustration of this mimicry was found by the author in a case where a cancer of the stomach showed a striking tendency to haemorrhage; the patient actually died from the effects of a large haematemesis. There were numerous secondary tumours in the liver, which looked almost like masses of blood. The delicate character of the vessels had been repeated in the secondary tumours, and bleeding was characteristic of them as well as of the primary growth.
The cancerous tissue is much more prone to degenerations and secondary changes than is normal tissue. Fatty degeneration is very frequent. (See Fig. 109.) This may, in quickly growing tumours, affect considerable portions, so as to give rise to an appearance like caseation. In more chronic cases, the fatty degeneration affects more the individual cells. The degenerated cells are readily absorbed, and this often leads to a relative preponderance of the stroma. Thus cancers frequently shrink and become cicatricial in their older or central parts. This may lead to dimpling of the surface of a tumour, as we often see -in cancers of the liver, producing the so-called Umbilication. Mucous and Colloid degeneration are not infrequent in cancers. They occur to a minor degree in many cancers of the intestine, but in a higher degree they are so characteristic as to give a special name to a form of cancer. (See Colloid cancer).
Fig. 109. - Fatty degeneration of cells in a cancer of the mamma: a, slightly affected; b, more so; c, completely fatty - the compound granular corpuscle, x 350.
Ulceration is the usual result in superficial cancers. As a general rule the cancerous ulcer is bounded by a prominent border, composed of tissue infiltrated with the growing tumour. (See Fig 110).
From what has been stated above, it will appear that cancer begins as a local growth of epithelium, accompanied by the formation of a connective tissue stroma of varying complexity. It is in many cases a well-formed but atypical tissue. In the secondary extension the other tumours bear a definite material relation to the primary one. They arise by the implantation of grafts, first, as a rule, in the lymphatic glands, and secondly, it may be, in parts further removed. As the primary cancer sends offshoots amongst the tissues, and extends outwards to the lymphatic glands, it must usually be difficult to determine its limits, but if these limits can be determined, and the whole growth removed, then we must infer that the disease will be eradicated. It is exceedingly rare to find two primary cancers in the same person. In the great majority of cases, all the existing tumours are direct descendants of a single primary growth.
Various modes of classification have been adopted. That which we use here is not entirely satisfactory, but it is useful for practical purposes.