The cause of carcinoma is at present unknown. Our knowledge of carcinoma in the human being is built up on clinical and pathologic observations. These have led to certain conclusions as to the growth of carcinoma, which may be summed up approximately as follows:
Carcinoma in its beginning is a purely local disease of a circumscribed group of epithelial cells. The tumor invades the host in two ways: first, by contiguity, and second, by the establishment of colonies or metastases, which are endowed with the same activities as the primary tumor.
The contiguous growth invades lymph-channels early and regularly, the blood circulation rather incidentally, irregularly and, we may say, less frequently. The primary tumor is subject to changes in two ways: first, degeneration, and second, infection. The metastases established especially along the lymphatic system are subject to the same changes, necrosis taking place in them and infection reaching them through