Differentiated tumors include squamous cell carcinoma with keratinization and without it, as well as highly and moderately differentiated adenocarcinoma. Considering the special biological properties of squamous cell low-grade lung cancer, poorly differentiated adenocarcinoma and undifferentiated forms of lung cancer, expressed in excessively malignant growth, a tendency to early, extensive lymph and hematogenous metastasis, the similarity of clinical manifestations, in order to develop issues of a unified therapeutic tactics, they are distinguished a group of low-grade lung cancers (Blinov N.N., 1984).
Very important in practical terms regarding the histological structure of lung cancer, is the position: the lower the differentiation of the tumor, the more malignant it is. Given this sign, for each histological type of lung cancer, peculiar developmental features have been established. Thus, highly differentiated squamous cell carcinoma grows relatively slowly, it is slightly prone to early and extensive lymphogenous and hematogenous metastasis. A study of its growth rates showed that from the moment
the occurrence of a tumor until it reaches 1.0 cm, a time of 13.2 years passes. Adenocarcinoma also develops relatively slowly and its growth rate is 7.2 years, but at the same time, a clear tendency of this histological type of lung cancer to early hematogenous dissemination is noted . Undifferentiated types of cancer, especially small cell cancers, are characterized by particularly rapid and rapid development. From the onset of occurrence to the achievement of 1.0 cm, they pass no more than 2.5 years. At the same time, a rather early and extensive lymphogenous and hematogenous metastasis is characteristic. A particularly significant variety of individual characteristics and heterogeneity is observed in lung cancer of small cell structure. In practical terms, the important point is that even with this histological type of lung cancer, there is always the so-called local-regional stage of development, characterized only by local manifestations of tumor growth. True, in comparison with other histological types of lung cancer in the small cell structure of the tumor, the local-regional stage of development is noticeably shorter.
The differences in the histological structure of cancer are also reflected in the relationship of the growing tumor with the tissue structures of the lung.
In many cases of squamous cell carcinoma, it is possible to note a mismatch between the development of the stroma and parenchyma of the tumor. Moreover, both previously existing and newly forming blood and lymph vessels cannot provide blood supply to the growing tumor. This leads to its collicational necrosis and decay, especially in large tumors located in the peripheral sections of the lung.
With undifferentiated cancers, the growth of metastases of the primary tumor is often outstripped, as well as its infiltrating, peribronchial, perivasal spread in the lung and beyond.
These features of the histogenesis of individual histological forms of lung cancer often largely determine the significant prevalence of blastomatous changes and the peculiarity of medical and surgical tactics.