A cancer is a malignant tumour which originates in epithelium. The cancer cells are derived by proliferation from already existing epithelium, and they invade the sub-epithelial connective tissue in the form of simple or branching columns. These columns are enclosed in spaces—termed alveoli—which are probably dilated lymph spaces, and which communicate freely with the lymph vessels. The cells composing the columns and filling the alveoli vary with the character of the epithelium in which the cancer originates. The malignancy of cancer depends on the tendency which the epithelium has of invading the tissues in its neighbourhood, and on the capacity of the cells, when transported elsewhere by the lymph or blood-stream, of giving rise to secondary growths.
Cancer may arise on any surface covered by epithelium or in any of the secreting glands of the body, but it is much more common in some situations than in others. It is frequently met with, for example, in the skin, in the stomach and large intestine, in the breast, the uterus, and the external genitals; less frequently in the gall-bladder, larynx, thyreoid, prostate, and urinary bladder.
Tissues appear to be most liable to cancer when, having attained maturity, they enter upon the phase of decadence or involution, and this phase is reached by different tissues at different periods. It is not so much, therefore, the age of the person in whom it occurs, as the age of the tissue in which it arises, that determines the maximum incidence of cancer. Cancer of the stomach appears and attains a maximum frequency earlier than cancer of the skin; cancer of the uterus and mamma is more frequent towards the decline of reproductive activity than in the later years of life; rectal cancer is not infrequently met with during the second and third decades. There is evidence that the irritation caused by alcohol and tobacco plays a part in the causation of cancer, in the fact that a large proportion of those who become the subjects of cancer of the mouth are excessive drinkers and smokers.
A cancer may appear as a papillary growth on a mucous or a skin surface, as a nodule in the substance of an organ, or as a diffuse thickening of a tubular organ such as the stomach or intestine. The absence of definition in cancerous tumours explains the difficulty of completely removing them by surgical measures, and has led to the practice of complete extirpation of cancerous organs wherever this is possible. The boundaries of the affected organ, moreover, are frequently transgressed by the disease, and the epithelial infiltration implicates the surrounding parts. In cancer of the breast, for example, the disease often extends to the adjacent skin, fat, and muscle; in cancer of the lip or tongue, to the mandible; in cancer of the uterus or intestine, to the investing peritoneum.
In addition to its tendency to infiltrate adjacent tissues and organs, cancer is also liable to give rise to secondary growths. These are most often met with in the nearest lymph glands; those in the neck, for example, becoming infected from cancer of the lip, tongue, or throat; those in the axilla, from cancer of the breast; those along the curvatures of the stomach, from cancer of the pylorus; and those in the groin, from cancer of the external genitals. In lymph vessels the cancer cells may merely accumulate so as to fill the lumen and form indurated cords, or they may proliferate and give rise to secondary nodules along the course of the vessels. When the lymphatic network in the skin is diffusely infected, the appearance is either that of a multitude of secondary nodules or of a diffuse thickening, so that the skin comes to resemble coarse leather. On the wall of the chest this condition is known as cancer en cuirasse. Although the cancer cells constantly attack the walls of the adjacent veins and spread into their interior at a comparatively early period, secondary growths due to dissemination by the blood-stream rarely show themselves clinically until late in the course of the disease. It is probable that many of the cancer cells which are carried away in the blood or lymph stream undergo necrosis and fail to give rise to secondary growths. Secondary growths present a faithful reproduction of the structure of the primary tumour. Apart from the lymph glands, the chief seats of secondary growths are the liver, lungs, serous membranes, and bone marrow.
It is generally believed that the secondary growths in cancer that develop at a distance from the primary tumour, those, for example, in the medullary canal of the femur or in the diploë of the skull occurring in advanced cases of cancer of the breast, are the result of dissemination of cancer cells by way of the blood-stream and are to be regarded as emboli. Sampson Handley disagrees with this view; he believes that the dissemination is accomplished in a more subtle way, namely, by the actual growth of cancer cells along the finer vessels of the lymph plexuses that ramify in the deep fascia, a method of spread which he calls permeation. It is maintained also that permeation occurs as readily against the lymph stream as with it. He compares the spread of cancer to that of an invisible annular ringworm. The growing edge extends in a wider and wider circle, within which a healing process may occur, so that the area of permeation is a ring, rather than a disc. Healing occurs by a process of “peri-lymphatic fibrosis,” but as the natural process of healing may fail at isolated points, nodules of cancer appear, which, although apparently separate from the primary growth, have developed in continuity with it, peri-lymphatic fibrosis having destroyed the cancer chain connecting the nodule with the primary growth. This centrifugal spread of cancer is clearly seen in the distribution of the subcutaneous secondary nodules so frequently met with in the late stages of mammary cancer. The area within which the secondary nodules occur is a circle of continually increasing diameter with the primary growth in the centre.
In the rare cases in which the skin of the greater part of the body is affected, the nodules rarely appear below the level of the deltoid or the middle third of the thigh, the patient dying before the spread can reach the distal portions of the limbs.
Handley argues against the embolic origin of the metastases in the bones because of the rarity of these in the bones of the distal parts of the limbs, because of the fact that secondary cancer of the femur nearly always commences in the upper third of the shaft, which harmonises with the intimate connection of the deep fascia with the periosteum over the great trochanter, thus favouring invasion of the bone marrow when permeation has spread thus far. He claims support for the permeation theory from the fact that the humerus is rarely involved below the insertion of the deltoid, and that spontaneous fracture of the femur is three times more common on the side on which the breast cancer is situated.
The tumour tissue may undergo necrosis, and when the overlying skin or mucous membrane gives way an ulcer is formed. The margins of a cancerous ulcer (Fig. 57) are made up of tumour tissue which has not broken down. Usually they are irregular, nodularly thickened or indurated; sometimes they are raised and crater-like. The floor of the ulcer is smooth and glazed, or occupied by necrosed tissue, and the discharge is watery and blood-stained, and as a result of putrefactive changes may become offensive. Hæmorrhage is rarely a prominent feature, but discharge of blood may constitute a symptom of considerable diagnostic importance in cancer of internal organs such as the rectum, the bladder, or the uterus.
The Contagiousness of Cancer.—A limited number of cases are on record in which a cancer appears to have been transferred by contact, as from the lower to the upper lip, from one labium majus to the other, from the tongue to the cheek, and from one vocal cord to the other; these being all examples of cancer involving surfaces which are constantly or frequently in contact. The transference of cancer from one human being to another, whether by accident, as in the case of a surgeon wounding his finger while operating for cancer, or by the deliberate introduction of a portion of cancerous tumour into the tissues, has never been known to occur. It is by no means infrequent, however, that when recurrence takes place after an operation for the removal of cancer, the recurrent nodules make their appearance in the main scar or in the scars of stitches in its neighbourhood. In the lower animals the grafting of cancer only succeeds in animals of the same species; for example, a cancer taken from a mouse will not grow in the tissues of a rat, but only in a mouse of the same variety as that from which the graft was taken.
While cancer cannot be regarded as either contagious or infectious, it is important to bear in mind the possibility of infection of a wound with cancer when operating for the disease. A cancer should not be cut into unless this is essential for purposes of diagnosis, and the wound made for exploration should be tightly closed by stitches before the curative operation is proceeded with; the instruments used for the exploration must not be used again until they have been boiled. The greatest care should be taken that a cancer which has softened or broken down is not opened into during the operation.
Investigations regarding the cause of cancer have been prosecuted with great energy during recent years, but as yet without positive result. It is recognised that there are a number of conditions which favour the development of cancer, such as prolonged irritation, and a considerable number of cases have been recorded in which cancer of the skin of the hands has followed prolonged and repeated exposure to the Röntgen rays.
The Alleged Increase of Cancer.—Regarding the alleged increase of cancer, it may be pointed out that it is impossible to ascertain how much of the apparent increase is due to more accurate diagnosis and improved registration. It is probable also that some increase has taken place in consequence of the increased average duration of life; a larger proportion of persons now reach the age at which cancer is frequent.
The prognosis largely depends on the variety of cancer and on its situation. Certain varieties—such as the atrophic cancer of the breast which occurs in old people, and some forms of cancer in the rectum—are so indolent in their progress that they can scarcely be said to shorten life; while others—such as the softer varieties of mammary cancer occurring in young women—are among the most malignant of tumours. The mode in which cancer causes death depends to a large extent upon its situation. In the gullet, for example, it usually causes death by starvation; in the larynx or thyreoid, by suffocation; in the intestine, by obstruction of the bowels; in the uterus, prostate, and bladder, by hæmorrhage or by implication of the ureters and kidneys. Independently of their situation, however, cancers frequently cause death by giving rise to a progressive impairment of health known as the cancerous cachexia, a condition which is due to the continued absorption of poisonous products from the tumour. The patient loses appetite, becomes emaciated, pale, and feverish, and gradually loses strength until he dies. In many cases, especially those in which ulceration has occurred, the addition of pyogenic infection may also be concerned in the failure of health.
Treatment.—Removal by surgical means affords the best prospect of cure. If carcinomatous disease is to be rooted out, its mode of spread by means of the lymph vessels must be borne in mind, and as this occurs at an early stage, and is not evident on examination, a wide area must be included in the operation. The organ from which the original growth springs should, if practicable, be altogether removed, because its lymph vessels generally communicate freely with each other, and secondary deposits have probably already taken place in various parts of it. In addition, the nearest chain of lymph glands must also be removed, even though they may not be noticeably enlarged, and in some cases—in cancer of the breast, for example—the intervening lymph vessels should be removed at the same time.
The treatment of cancer by other than operative methods has received a great deal of attention within recent years, and many agents have been put to the test, e.g. colloidal suspensions of selenium, but without any positive results. Most benefit has resulted from the use of radium and of the X-rays, and one or other should be employed as a routine measure after every operation for cancer.
It has been demonstrated that cancer cells are more sensitive to radium and to the Röntgen rays than the normal cells of the body, and are more easily killed. The effect varies a good deal with the nature and seat of the tumour. In rodent cancers of the skin, for example, both radium and X-ray treatment are very successful, and are to be preferred to operation because they yield a better cosmetic result. While small epitheliomas of the skin may be cured by means of the rays, they are not so amenable as rodent cancers.
Cancers of mucous membranes are less amenable to ray treatment because they are less circumscribed and are difficult of access. In cancers under the skin, the Röntgen rays are less efficient; if radium is employed, the tube containing it should be inserted into the substance of the tumour after the method described in connection with sarcoma—and another tube should be placed on the overlying skin.
In the employment of X-rays and of radium in the treatment of cancer, experience is required, not only to obtain the maximum effect of the rays, but to avoid damage to the adjacent and overlying tissues.
Ray treatment is not to be looked upon as a rival but as a powerful supplement to the operative treatment of cancer.