The following guidelines were developed for the medical assessment services of the German Pension Insurance Federal Institution. Starting from day-to-day practice, criteria and attributes to guide decisions for a systemisation of the sociomedical assessment of performance in breast cancer were compiled. The guidelines aim at standardising the sociomedical assessment of performance and help to make the decision-making process more transparent, e. g., for the assessment of applications for decreased earning capacity benefits. The guidelines summarise typical manifestations of breast cancer and describe the necessary medical information for the sociomedical assessment of performance. Relevant assessment criteria for the medical history, clinical examination, and for diagnostic tests are illustrated. The assessment of the individual's capacity is outlined, taking occupational factors into account. Following the determination of dysfunctions, the remaining abilities and disabilities, respectively, are deduced and compared with occupational demands. Finally, inferences are drawn regarding the occupational capacity of the individual.