Neoplasm is the cause of a double disease of the body, i.e. with two faces (Janus disease), which means both the presence of cancer cells and the secondary disorders of the immune system function caused by them. The second possibility is a temporary decrease in immunity, caused by e.g. influenza, and revealing a neoplastic disease. Neoplasms are induced by both genetic and epigenetic factors (Fig. 1), giving different types of mono- and polyclonal metastases and cross-spreading (Fig. 2). Recently, exosomes have been ascribed an important role in the formation of metastases. They transfer information between normal and cancer cells by horizontal transfer and „teach” myeloid cells to move to the pre-metastatic niche and the metastatic deposit. In carcinogenesis, the main role is played by long-lived cancer stem cells, as well as differentiated cells after they have gained the ability to self-renew, as in stem cells. The paper also presents examples of neoplasms accompanied by a second, primary neoplasm in the same system or in the vicinity. Multiple primary malignances (MPM) associated with them have also been described. With the help of the so-called strange attractor, an attempt was made to describe the behavior of cancers in connection with the phenomenon of deterministic chaos based on the process of entropy. Distinguishing between chaotic and stochastic (random) systems is very difficult in biology.