The influence of embryonal bursectomy on benzpyrene-induced sarcoma of the chicken

[Mechanisms of malignant growth (author's transl)]

Analysis of invasive malignancy focuses on the particularly high growth rate of tumor cells, and on the aggressive mechanisms of histolysis favoring the infiltration of the malignant cells into the surrounding tissue. Specific significance is attributed to a certain enzyme directed against type IV collagen, and to the auto-locomotion of tumor cells, properties that may also explain the highly selective process of metastazation in at least three consecutive steps: Tumor cells invade a blood or lymph vessel, they are transported along blood or lymphatic pathways, and they eventually infiltrate foreign tissue after penetration and destruction of blood of lymph vessel walls. Among the factors involved in the process of metastazation, special interest is due to blood coagulation and to the coexistence of different tumor cell subpopulations within a primary. These features of malignant growth are based on the loss of functional differentiation as manifested e.g. in the loss of tissue-specific nuclear chromatin structures. Tumor development is triggered by the so-called primary factors which always affect the DNA, i.e. the cell genome. Chemical carcinogens, viruses, and shortwave or ionizing irradiation induce DNA defects which, however, will be reversed and mended by special repair mechanisms in most cases. Thus, the actual development and spread of malignancy is ultimately due to deficient reparation. Co-factors favorizing and promoting carcinogenesis may shorten the latency period, among other several specific chemicals and hormones. Based on current knowledge of tumor dormancy a new concept is proposed for the chronological and morphological sequence of carcinogenesis: Following the development of a primary tumor certain as yet undefined growth factors and especially immunological factors may be responsible for the development of a progressive tumor disease.