The misunderstanding of the R Classification-a survey amongst medical specialties treating breast cancer.

Frequent discussions in the tumour board about the Residual tumour (R) Classification of the UICC's "TNM Classification of Malignant Tumours", especially in the case of breast surgery specimens, raised the question about differing interpretations amongst different medical specialties. Thus, we designed a survey about the R Classification with a special focus on breast cancer specimens. An online survey was conducted, where a web link to the survey was distributed via email to various medical professional societies dealing with breast cancer in Austria and Germany with the request to distribute the link to their members. The study population consisted of physicians of all educational levels of different medical professions, who deal with breast carcinomas in their daily routine. Two hundred two participants, of which 160 (79.2%) have more than 10 years' professional experience, took part in the survey; 88 (43.6%) were surgeons/gynaecologists, 80 (39.6%) pathologists, 19 (9.4%) radiation oncologists/ therapists, 8 (4.0%) radiologists, and 7 (3.5%) oncologists. We show that the R Classification is not completely mastered by anyone and that there are significant differences in the interpretation of the R Classification between different medical specialties. For better differentiation between the residual tumour (R Classification) of the TNM and a pure resection margin assessment, we suggest the use of a Resection margin (Rm) Classification to avoid further misunderstandings. To assist better multidisciplinary cooperation and to ensure better patient care all medical disciplines should be educated about the actual meaning and correct application of the R Classification.