Patrón infrecuente de respuesta patológica a la terapia sistémica primaria

Neoadjuvant chemotherapy (NACT) has become the standard treatment for high-risk breast cancer. The pathological study of post-NACT surgical specimens, always complex and still insufficiently standardised, remains the gold standard for the definitive assessment of response, the morphological patterns of which must be identified. Pathologists, therefore, must identify NACT-induced changes in both tumour cells and tumour-associated stroma, as well as in the background breast tissue. Residual tumour volume after NACT is a significant prognostic factor and different methods have been proposed to quantify it. The most commonly used are the RCB and Miller-Payne systems. Although both indices are capable of stratifying response, the RCB has greater predictive power. Neither, however, provides information on certain poorly recognised morphological response patterns that, even without residual stromal tumour, should not be considered complete pathological response and their biological significance and prognostic value are controversial. We present a case of pure lymphovascular residual tumour response, morphological characterisation, and differential diagnosis, together with the applicability of the RCB and Miller-Payne indices in these cases.