Carcinoma of the stomach is apt to involve the vessels in its neighbourhood either by direct extension or through the medium of the lymphatics. As a rule the veins are more affected than the arteries, and, in addition to a general infiltration of their walls, they not infrequently present masses of epithelial cells which project into their lumina. These small vegetations are liable to be swept off and to be carried by the blood into other viscera, where they develop into tumours of the same structure as the original growth. In other cases the vein becomes occluded by clot and the thrombus is subsequently infiltrated by cancer cells.
The fact that the veins of the stomach are chiefly directed into the portal system is sufficient to explain the inordinate frequency of metastatic deposits in the liver. These vary greatly both in number and size ; in some cases only one or two small nodules being present, while in others the whole organ seems to be converted into a mass of cancer. Secondary disease of the liver is most common in carcinoma of the central and cardiac regions of the stomach, and its development is often excessive when compared with the size of the original tumour. On the other hand, growths of the pylorus which produce contraction of the orifice are rarely accompanied by metastases in the liver (Table 7, p. 56). Occasionally the venous infection is limited to the wall of the stomach and is accompanied by thrombosis of the coronary, epiploic, or pyloric veins; but as a rule the portal trunk itself is affected, and becomes partially filled with masses of cancer (Pressat, Eendu), or even completely obstructed by them (Labbe, Contour).
Carcinoma may infect the blood of the systemic veins in three ways : by direct invasion of the inferior vena cava, by the extension to the hepatic veins of a growth of the liver, or by lymph conveyed through the thoracic or right lymphatic ducts. In every case its first effect is to produce secondary deposits in the lungs, a condition which is met with in nearly 8 per cent, of all cancers of the stomach. These metastases usually develop in the lower lobes, where they form rounded compact tumours of considerable size ; but occasionally they take the form of a miliary growth at one or other apex. The latter variety may closely resemble tubercle, both in its general appearance and also in its tendency to undergo softening and caseation. Brinton seems to have been convinced that implication of the liver greatly diminished the risk of pulmonary infection; but this view has not been supported by subsequent writers, nor does the fact that the liver was affected in 80 per cent, of our cases which presented pulmonary growths permit us to endorse it. Cancerous infection of the arterial system may be local or general. The former is chiefly observed in cases where the gastric growth has invaded the hepatic, coronary, or renal arteries, while the latter is nearly always the result of infection of the systemic veins. The fact that in cases of general infection the lungs are not always the seat of secondary growths seems to indicate that cancer cells are capable of passing through the pulmonary capillaries without producing embolism. After gaining an entrance to the left side of the heart, the morbid particles are immediately directed into the systemic arteries, and in this way may disseminate the disease throughout the body. The principal organs affected in this manner are, in their order of frequency-kidneys (4 per cent.), heart (2.3 per cent.), ovaries (2.3 per cent.), spleen (2 per cent.), bones (2 per cent.), uterus (1.5 per cent.), large intestine (.7 per cent.), and brain (.7 per cent.). The bones usually affected are the sternum, humerus (Marrotte), and sacrum (Bouveret) ; while disease of the brain is interesting, in that it is almost invariably associated with a tumour of the lung.