Summary: This paper presents a brief description of main ideas discussed in our study [1] devoted to system engineering approach to processes behind cancer development. More precisely we consider carcinogenesis and development of cancer disease in terms of propagation phenomena in biological networks. Our attention is focused on regulatory mechanisms which make cell cycle a fault tolerant system and on weak points of this system leading to mutagenesis and cancer progression. Other issues related to further development of the disease including angiogenesis and metastasis are mentioned.