Mention has already been made of the invasion of parts adjacent to the stomach by the continuous growth of gastric cancer. In this way lymphatic glands, the liver, the pancreas, the omenta, the transverse colon, the spleen, the diaphragm, the anterior abdominal wall, the vertebræ, the spinal cord and membranes, and other parts may be involved in the cancerous growth.

Under the head of Complications reference has already been made to various lesions which may be associated with gastric cancer. As regards the manifold complications caused by perforation of gastric cancer, in addition to what has already been said the article on gastric ulcer may be consulted. In general, the various fistulous communications caused by gastric cancer are less direct than those produced by gastric ulcer. The wasting of various organs of the body in cases of gastric cancer may be found on post-mortem examination to be extreme. Habershon mentions a case in which the heart of a woman forty years old weighed only 3½ ounces after death from cancer of the pylorus. As in other profoundly anæmic states, the embryonic or lymphoid alteration of the marrow of the bones is often present in gastric cancer.

PATHENOGENESIS.—The problems relating to the ultimate causation and origin of gastric cancer belong to the pathenogenesis of cancer in general. Our knowledge with reference to these points is purely hypothetical. It will suffice in this connection simply to call attention to Virchow's doctrine, that cancer develops most frequently as the result of abnormal or of physiological irritation, hence in the stomach most frequently at the orifices; and to Cohnheim's theory, that cancer as well as other non-infectious tumors originate in abnormalities in development, more specifically in persistent embryonic cells. According to the latter view, gastric cancer develops only in those whose stomachs from the time of birth contain such embryonic remnants. These unused embryonic cells may lie dormant throughout life or they may be incited to cancerous growth by irritation, senile changes, etc. According to Cohnheim's theory, the orifices of the stomach are the most frequent seat of cancer on account of complexity in the development of these parts.

For a full consideration of these theories the reader is referred to the section of this work on General Pathology.

DIAGNOSIS.—The presence of a recognizable tumor in the region of the stomach outweighs in diagnostic value all other symptoms of gastric cancer. The detection of fragments of cancer in the vomit or in washings from the stomach is of equal diagnostic significance, but of rare applicability. The discovery of secondary cancers in the liver, in the peritoneum, or in lymphatic glands may render valuable aid in diagnosis. Of the local gastric symptoms, coffee-ground vomiting is the most important. The relation between the local and the general symptoms may shed much light upon the case. While anorexia, indigestion, vomiting, and epigastric pain and tenderness point to the existence of a gastric affection, the malignant character of the affection may be surmised by the development of anæmia, emaciation, and cachexia more rapid and more profound than can be explained solely by the local gastric symptoms. The value to be attached in the diagnosis of gastric cancer to the absence of free hydrochloric acid from the contents of the stomach must still be left sub judice. The age of the patient, the duration, and the course of the disease are circumstances which are also to be considered in making the diagnosis of gastric cancer. These symptoms of gastric cancer have already been fully considered with reference to their presence and absence and to their diagnostic features.

It remains to call attention to the differential diagnosis between gastric cancer and certain diseases with which it is likely to be confounded. The points of contrast which are to be adduced relate mostly to the intensity and the frequency of certain symptoms. There is not a symptom or any combination of symptoms of gastric cancer which may not occur in other diseases. Hence the diagnosis is reached by a balancing of probabilities, and not by any positive proof. Notwithstanding these difficulties, gastric cancer is diagnosed correctly in the great majority of cases, although often not until a late stage of the disease. Errors in diagnosis, however, are unavoidable, not only in cases in which the symptoms are ambiguous or misleading, but also in cases in which all the symptoms of gastric cancer, including gastric hemorrhage and tumor, are present, and still no gastric cancer exists. Cases of the latter variety are of course rare.

In the absence of tumor the diseases for which gastric cancer is most liable to be mistaken are gastric ulcer and chronic gastric catarrh. In the following table are given the main points of contrast between these three diseases:

GASTRIC CANCER.GASTRIC ULCER.CHRONIC CATARRHAL GASTRITIS.
1. Tumor is present in three-fourths of the cases.1. Tumor rare.1. No tumor.
2. Rare under forty years of age.2. May occur at any age after childhood. Over one-half of the cases under forty years of age.2. May occur at any age.
3. Average duration about one year, rarely over two years.3. Duration indefinite; may be for several years.3. Duration indefinite.
4. Gastric hemorrhage frequent, but rarely profuse; most common in the cachectic stage.4. Gastric hemorrhage less frequent than in cancer, but oftener profuse; not uncommon when the general health is but little impaired.4. Gastric hemorrhage rare.
5. Vomiting often has the peculiarities of that of dilatation of the stomach.5. Vomiting rarely referable to dilatation of the stomach, and then only in a late stage of the disease.5. Vomiting may or may not be present.
6. Free hydrochloric acid usually absent from the gastric contents in cancerous dilatation of the stomach.6. Free hydrochloric acid usually present in the gastric contents.6. Free hydrochloric acid may be present or absent.
7. Cancerous fragments may be found in the washings from the stomach or in the vomit (rare).7. Absent.7. Absent.
8. Secondary cancers may be recognized in the liver, the peritoneum, the lymphatic glands, and rarely in other parts of the body.8. Absent.8. Absent.
9. Loss of flesh and strength and development of cachexia usually more marked and more rapid than in ulcer or in gastritis, and less explicable by the gastric symptoms.9. Cachectic appearance usually less marked and of later occurrence than in cancer; and more manifestly dependent upon the gastric disorders.9. When uncomplicated, usually no appearance of cachexia.
10. Epigastric pain is often more continuous, less dependent upon taking food, less relieved by vomiting, and less localized, than in ulcer.10. Pain is often more paroxysmal, more influenced by taking food, oftener relieved by vomiting, and more sharply localized, than in cancer.10. The pain or distress induced by taking food is usually less severe than in cancer or in ulcer. Fixed point of tenderness usually absent.
11. Causation not known.11. Causation not known.11. Often referable to some known cause, such as abuse of alcohol, gormandizing, and certain diseases, as phthisis, Bright's disease, cirrhosis of the liver, etc.
12. No improvement or only temporary improvement in the course of the disease.12. Sometimes a history of one or more previous similar attacks. The course may be irregular and intermittent. Usually marked improvement by regulation of diet.12. May be a history of previous similar attacks. More amenable to regulation of diet than is cancer.

The diagnosis between gastric cancer and gastric ulcer is more difficult than that between cancer and gastritis, and sometimes the diagnosis is impossible. The differential points mentioned in the table are of very unequal value. An age under thirty, profuse hemorrhage, and absence of tumor are the most important points in favor of ulcer; tumor, advanced age, and coffee-ground vomiting continued for weeks are the most important points in favor of cancer. As cancer may have been preceded by ulcer or chronic gastritis for years, it is evidently unsafe to trust too much to the duration of the illness. As has already been said, it is best to place no reliance in the differential diagnosis upon the character of the pain. Any peculiarities of the vomiting, the appetite, or the digestion are of little importance in the differential diagnosis. Cachexia is of more importance, but it is to be remembered that ulcer, and even chronic gastritis in rare instances, may be attended by a cachexia indistinguishable from that of cancer. Cases might be cited in which very decided temporary improvement in the symptoms has been brought about in the course of gastric cancer, so that too much stress should not be laid upon this point. Enough has been said under the Symptomatology with reference to the diagnostic bearings of the absence of free hydrochloric acid from the stomach, of the presence of cancerous fragments in fluids from the stomach, and of secondary cancers in different parts of the body.

One must not lose sight of the fact that the whole complex of symptoms, the order of their occurrence, and the general aspect of the case, make an impression which cannot be conveyed in any diagnostic table, but which leads the experienced physician to a correct diagnosis more surely than reliance upon any single symptom.