We mentioned already that certain pathological conditions prepare the soil for the subsequent development of cancer, such as for instance lupus, chronic ulceration of the leg. But there are numerous other morbid conditions which stand in a certain causal relation to the growth of cancer. Gastric carcinoma originates in a considerable number of cases at the site of a previous ulcer of the stomach. Long-continued suppuration in the middle ear, fistules of various parts of the body may be followed by the development of cancer; so may certain affections, in which either certain parts of the skin or the mucosa are covered by plaques of horn, so-called (leukoplakia of the tongue and vulva, psoriasis). In the mammary gland chronic inflammation may lead to the subsequent development of cancer. Carcinoma may be preceded in the thyroid by goitre, in the liver, by chronic inflammation leading to an increase in fibrous tissue (cirrhosis), in the prostate by hypertrophy which is relatively common in old men. Inasmuch as certain conditions predisposing to cancer may be caused by syphilis, also syphilitic infection is indirectly one of the causes of cancer.
We mentioned previously that xeroderma pigmentosum, a congenital lesion of the skin, becomes usually cancerous. We furthermore know that certain at first benign tumors may later be transformed into cancers. Thus papillomata (polypus or cauliflower-like outgrowths) very often precede cancer of the small and large intestines or of the bladder. These papillomata are in the intestines frequently caused by preceding long-continued irritation; in certain cases however they are congenital. Pigmented moles of the skin if constantly irritated may be transformed into a pigmented cancer which is often very virulent.
At first benign tumor-like proliferations of the epithelium of the liver, mammary gland, ovaries, uterus, and especially glandular tumors (so-called adenomata) may later become transformed into carcinoma. As we have already mentioned, certain parts of teratomata at various places of the body are not rarely changed into carcinoma or sarcoma. The usually benign muscle tumors of the uterus (myomata) are in 6-10 per cent, of all the cases transformed into tumors resembling sarcomata, a change which does usually not take place before the patient has reached the fortieth year. In other cases, however, such myomata of the uterus are only the indirect cause of the development of cancer, the mucosa in their neighborhood becoming converted into carcinoma. Possibly the constant irritation caused through the pressure of the muscle tumors upon the epithelial lining of the organ may be responsible for this transformation. Furthermore, fat tumors (lipomata) may occasionally assume a malignant growth and become sarcomatous or soft, mucus-producing tumors (myxomata) which may be malignant and may metastasize.
Long-continued irritation is not always necessary but in certain
