Extra-organ metastatic retroperitoneal tumor of the right iliac region in a 26-year-old female patient. Problem: unclassifiable tumor

The basis of current oncology is the verification of the disease. Only after the pathomorphological establishment of a clinical diagnosis, the treatment tactics of a particular patient are collectively selected. Now, in most cases, only pathomorphological diagnostics is not enough, it is necessary to conduct immunohistochemical and even molecular genetic researches, some of which are possible only in large federal referral centers. However, despite the existence of wide possibilities and detailed pathohistological classifications of neoplasms, with the development of modern diagnostic technologies, the medical community began to understand that some pathological processes go beyond the developed methods of diagnosis and cannot be verified within existing classifications. This way, patients with unclassifiable tumors currently do not have the opportunity to receive antitumor treatment based on evidence-based medicine, due to the lack of large-scale researches and clinical recommendations for the treatment of these types of tumors. The main purpose of the article is to once again draw the attention of the oncological community to the existence of unclassifiable tumors, in order to continue collecting information and jointly develop tactics for the diagnosis and treatment of these rare tumors.