Partial breast irradiation: targeting volume or breast molecular subtypes?

The eligibility criteria for partial breast irradiation (APBI) are mainly based on histopathological factors, which not always explain the clinical behaviour of breast cancers. International guidelines represent useful platform to collect data for continued refinement of patient selection, but the clinical applicability to APBI series showed some limitations, particularly among the intermediate and high-risk groups. The heterogeneity of APBI techniques, along with the heterogeneity of breast cancer, generates clinical results, where the predictive value of the histopathological factors can assume different weight. There is a need of further refinement and implementation of risk factors. Currently, the impact of breast cancer subtype on local control is matter of investigation, and treatment decision about radiotherapy is generally made without regard to the breast cancer subtype. However, receptor status information is easily available and some histopathological factors have not a definite role, there is no uniform interpretation. As molecular classification becomes more feasible in the clinical practice, it will provide added value to conventional clinical tumour characteristics in predicting local recurrence in breast cancer and may play an important role as predictor of eventual patient outcomes.