The problem of postoperative skin defect is relevant in oncology, especially in the surgical treatment of patients with breast cancer. Aim of study. Topographic-anatomical, mathematical and technical justification of method of laxative incisions when replacing significant skin defects of the anterior chest wall after radical mastectomy (ME). Materials and methods. The work included data on 81 patients undergoing treatment in the oncology department of the Clinical Hospital named after Peter the Great of the North-Western State Medical University named after I.I. Mechnikov from 2003 to 2011, the age of the patients ranged from 33 to 91 years, while the median was 59 (95% confidence interval — CI from 54 to 64) years, and the average age was 60 (95% CI from 57 to 63) years. At the age less than 50, there were 20 (24.7%) patients, age interval 50—59 years — 22 (27.2%), age interval 60—69 years —16 (19.8%) and at the age of 70 years and older — 23 (28.4%)) patients. Most patients underwent modified radical ME — 66 (81.5%), simple ME was performed in 4 (4.9%) patients, sanitary amputation — in 11 (13.6%) women. For the purpose of mathematical modeling, comprehensive study and analysis of the proposed methodology for orientation of laxative sections, Abaqus CAE software and the Solidworks 2016 software package were used. Results. The overall 3-year survival of patients was 68.4±5.3%. A total of 9 (11%) complications («events») developed — relapses, progression, which occurred between 8 and 106 months (average 28.5 months, median 17 months). The non-event survival rate was 62.6±5.5%. If radical surgery was possible, the overall survival rate was 72.1±5.6%, and if impossible, it decreased to 45.5±15% (χ2=3.6388, df=1, log-rank criterion 0.0493). In the mathematical modeling environment of Abaqus CAE, virtual mathematical models were created: model a, which imitates proposed geometric configuration with the location of cut centers at the intersection points of confocal ellipses and hyperbolas, model b, in which laxative cuts are located without any order parallel to the long axis of defect ellipse, and model c, similar to the previous one, but with a large number of cuts. It is shown that the critical tension value in model a is higher (374.4 Pa) than in model b (365.4 Pa) and similar to model c (330.0 Pa). Our model demonstrates a great ability to deform: the deformation scale factor is + 3,485e + 03, for model b + 3,461e + 03 and for model c + 3,355e + 03. Conclusions. Applying a series of laxative incisions is one of the best ways to solve the problem of closing extensive skin defects of the anterior chest wall and healing of wound after radical ME. Our proposed mathematical model of orientation and location of laxative cuts can reduce surgical trauma