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This article reviews key changes in the current 2013 World Health Organization Classification of soft tissue tumors.

General principles of the second review of the soft tumours classification and brief description of nosological unities absent in the first edition are presented.

Sixty-three patients with malignant and benign tumors of soft tissues were examined making use of magnetic resonance computer-aided tomography (MRT). This method was found effective in the diagnosis of soft tissue tumors, permitting the detection of tumor connection with the adjacent structures. In some cases MRT helped differentiate between malignant and benign soft tissue tumor growth, e.g. liposarcoma, malignant fibrous histiocytoma, lipoma, desmoid, hematoma. MRT may be effectively used in the diagnosis of soft tissue formations.

Analysis of CT data on 213 patients with soft tissue and trunk tumors has shown that a majority of malignant and benign tumors have a similar picture (except lipoma). Features of the contours of a tumor and its inner structure do not permit the assessment of its nature. The only significant differential-diagnostic sign of malignant soft tissue tumors is destruction of an adjacent bone, noted in 17.6%. The majority of malignant and benign soft tissue tumors (70.9%) on CT scans look like a single node; recurrent tumors look multinodular (78.2%). Verification of soft tissue tumors, revealed by CT, should be done using morphological methods.

Analysis of CT data on 213 patients with soft tissue and trunk tumors has shown that a majority of malignant and benign tumors have a similar picture (except lipoma). Features of the contours of a tumor and its inner structure do not permit the assessment of its nature. The only significant differential-diagnostic sign of malignant soft tissue tumors is destruction of an adjacent bone, noted in 17.6%. The majority of malignant and benign soft tissue tumors (70.9%) on CT scans look like a single node; recurrent tumors look multinodular (78.2%). Verification of soft tissue tumors, revealed by CT, should be done using morphological methods.

108 tumors reckoned in the file of the N. N. Petrov Research Institute of Oncology as vascular neoplasms were studied microscopically and histochemically. Malignant hemangioendotheliomas showed formation of vascular structures (a microscopic sign) and expression of specific markers of the endothelium, viz. clotting factor VIII and Ulex Europaeus lectin (immunohistochemical signs). Expression of these signs is determined by degree of tumor differentiation. According to these pathognomonic criteria, only 24 tumors observed at the Institute during 53 years proved hemangioendotheliomas.

Two cases of congenital tumour-like conditions of the connective tissue are described. The identity of both pathological processes classified as congenital local fibromatosis is established. It is suggested to introduce "local congenital fibromatosis" into the classification of tumour-like diseases of the connective tissue.

Current concepts on fibromatosis are presented, main works dealing with this subject are analysed, the existing classifications are discussed. Clinico-morphological characteristics of individual forms of fibromatosis is given on the basis of Allen's classification. The emphasis is made on the difficulties of diagnosis of inborn local forms of fibromatosis.

The clinicoroentgenological data in 45 cases (20 males and 25 females, average age 50.3 years) of soft tissue liposarcomas, histologically subdivided into 28 myxoid, 12 polymorphic and 5 round-cell tumors were compared. The means case history was 3.2 years (3.8 years--for myxoid and 2.2 years for polymorphic and roundcell liposarcomas). In 95.6% of cases, tumor sites were in the musculare of the extremities, more frequently, legs. Tumors were rather large in size (average 16.5 cm). Myxoid tumors developed slowly, causing no pain. The radiograms of these tumors showed multiple tumor nodes, reduced shadow density, structural heterogeneity, distinct contours, infrequent cutaneous infiltration and secondary changes in bones. Signs of malignancy were indistinct in angiograms. Clinically and roentgenologically, round-cell liposarcomas resembled most other types of soft tissue sarcomas. Polymorphic tumors had many features in common both with myxoid and round-cell neoplasms.

Ultrastructure of both liposarcomas of different histological types and those with non-verified diagnosis are studied. Liposarcomas are shown to contain a basic complex of ultrastructural features of lipid differentiation and different histological types of these tumours have, in principle, identical features varying in the degree of their expression. The questions of a differential diagnosis of liposarcomas and other tumours can be successfully solved on the basis of the above findings, and even more, a group of liposarcomas with a severe cataplasia that does not have histological analogues may be distinguished. The results allowed to work out an ultrastructural classification of liposarcomas in which the degree of cataplasia is directly taken into account.

Clinico-morphological characterization of the malignant fibrous histiocytoma (MFH) of soft tissues in 142 patients is presented. According to the authors' data MFH is the most frequent tumour among soft tissue malignant neoplasms (15,7%) in adult patients. The age of patients is predominantly from 40 to 70, the most frequent site is a lower limb (thigh). A typical morphological variant of MFH clearly dominates (73%): there is a tendency to the development of an inflammatory variant at the retroperitoneal tumour site. Recurrences in all group of patients (104) who were followed-up were in 68,3%, metastasis in 45,2%, the 5-year survival in 59,6% of cases. A clear-cut dependence of these indices upon the depth of tumour location soft tissues, node size, tumour site is noted. In view of pronounced domination of a MFH typical variant the final conclusion on the feasibility of separation of other variants can be only made on the basis of a much greater number of cases.