Because they provide patient-specific guideline-based recommendations, clinical decision support systems (CDSSs) are expected to promote the implementation of clinical practice guidelines (CPGs). OncoDoc2 is a CDSS applied to the management of breast cancer. However, despite it was routinely used during weekly multidisciplinary staff meetings (MSMs) at the Tenon Hospital (Paris, France), the compliance rate of MSMs' decisions with CPGs did not reach 100%. Formal Concept Analysis (FCA) has been applied to elicit formal concepts related to non-compliance. A statistical pre-treatment of attributes has been proposed to leverage FCA and discriminate between compliant and non-compliant decisions. Among the 1,889 decisions made over a 3 year-period, 199 decisions of recommended re-excisions have been considered for analysis. In this sample, non-compliance was explained by uncommon clinical profiles and specific patient-centred clinical criteria.