Cancer of the lung often reverses the rule that carcinoma occurs most frequently in the female, Hasse, Kohler, and Cockle giving a majority of cases among males. It has been met with in childhood and in extreme old age, but is more common in the middle periods of life, from twenty to sixty years.
PREDISPOSING AND EXCITING CAUSES.—The predisposing and exciting causes of malignant pulmonary disease are involved in the obscurity that surrounds the development of all neoplasms.
PATHOLOGICAL ANATOMY.—Clinically speaking, cancer in the pulmonary tissues includes the scirrhous or encephaloid neoplasms. The colloid, enchondromatous, or fibromatous growths have been recorded as possible tumors, but possess only a pathological interest.
Malignant disease may commence in, or ultimately implicate, one or all of the pulmonary tissues; secondary neoplasms have been experimentally produced by lodgment in the lung of living cellular particles which grew centrally by virtue of inherent cell-proliferation, independently of changes produced in the surrounding tissues. Cancer of the lungs, whether primary or secondary, usually originates near the roots of the lungs, implicating the mucous and submucous membranes of the bronchi, sometimes commencing in its small mucous follicles. The bronchial passages and the lymph-channels become the viaducts along which the growth proceeds in its march of invasion, involving most frequently the posterior portion of the middle lobe. The apices of the lungs may be implicated, but not primarily, as in tuberculosis. The mediastinal lymphatics are originally involved in an unestimated number of cases, or enlargement of these glands is coexistent with the development of pulmonary cancer. The enlargement of the mediastinal glands is sometimes moderate, but an enormous mass may be formed. (Vide [MEDIASTINAL TUMORS].)
Carcinoma is found in masses varying in size from a hempseed to an orange or larger, and since its distribution follows the lymph-channels in their circuitous route through the lung, we can account for the wide distribution of the nodular masses of secondary cancer. The isolated nodules present an ovoid outline, sometimes situated near the pleural surface, in contrast with the larger formations which affect the roots of the lungs.
The primary malignant formation presents a single large mass of infiltration, possibly associated with a few small nodules scattered throughout the lungs; the right lung is conceded to be the most frequently affected, but secondary cancer usually implicates both organs.
Cancer in the parenchyma of the lung may diminish or occlude the lumen of the bronchial tubes, or they may be filled with cancerous matter and their walls perforated. The development of cancer along the distribution of the bronchial passages shows us how readily chronic bronchitis may occur as a complication and form a confusing element in the diagnosis. The remaining pulmonary tissues may escape anatomical change, or from pressure atrophic or hypertrophic emphysema or collapse may ensue. These changes, together with the similarity to a fibroid phthisical process which many cases suggest, must be borne in mind in making a diagnosis. Pulmonary apoplexy, or even gangrene, is an incident in some of the clinical pictures of this disease, and embolism or thrombosis in other parts of the system may occur. The terminations of intra-thoracic cancer vary in accordance with the history of these growths elsewhere. Infiltration with blood or melanic deposition has been noticed; evacuation of the new growth through the bronchi may induce the development of cavities in the lungs, preceded or accompanied by suppuration, ulceration, or gangrene. In addition, hydro- or pyo-pneumothorax may occur by perforation or invasion of the pulmonary pleura.
Carcinoma of the pleura is usually secondary to its development in the lung, but it may be communicated from a similar process in the mammary gland by infection through the pectoral and intercostal muscles to the parietal pleura. Carcinomatous formations on the pleura are small and hard in scirrhous, but are larger in encephaloid, cancer. The minute spots of early formation are found scattered over the pleura like drops of wax. The thickened tissues, when they coalesce, undergo degeneration, and may form plaques of cartilaginous hardness. Large pleural growths may compress or nearly efface the lung, but are among the curiosities of medical literature.
Neuralgia may be occasioned when nodules impinge upon the intercostal nerves. Similar pressure is the cause of the pain in pulmonary cancer, except that induced by the pressure of mediastinal enlargement. Chronic pleural inflammation may be frequently developed by the new growth, and the diseased lung may become adherent to the inner surface of the sternum and ribs. The lung in other cases may be compressed or retracted, uncovering the heart and rendering the chest-walls smaller. The chest may be enlarged, especially if there is pleural effusion; usually the contour is unchanged.
Pleural effusions are frequent in the history of this disease: they may be passive, resulting from pressure on the azygos or hemiazygos veins, preventing the return of the blood from the pleural veins, or from mediastinal pressure. An inflammatory hydrothorax may be excited by the deposit of cancerous material in the pleura; and it is possible for these effusions to undergo purulent transformation or to become hemorrhagic. A hemorrhagic effusion when grouped with other symptoms may be considered an important evidence of malignant formation. The further history of pleural effusions in this association is usually an increase of such an amount as to necessitate removal by thoracentesis, but reabsorption is possible.