Correlation of MRI/PET rim enhancement in breast cancer: a delivery related phenomenon with therapy implications?

A 37-year-old woman presented with a large, inflammatory, grade 3 invasive ductal carcinoma of the breast and was treated with six cycles of neoadjuvant chemotherapy. Sequential dynamic contrast-enhanced MRI and 18Ffluoro-2-deoxy-D-glucose (FDG) PET were used to monitor response throughout therapy. The patient showed partial clinical and histo-pathological response to therapy. Although MRI and FDG uptake are based on entirely different physiological mechanisms, both initially showed a marked rim enhancement with low central signal before initiation of treatment (pretherapy). The final images, acquired after six cycles of therapy (post therapy), showed overall volume reduction and a marked increase in central volume MRI and FDG uptake. Uniformity of pretherapy tumour MRI relaxation values refutes tissue necrosis but pretherapy low central PET uptake refutes hypoxia. We therefore hypothesise a delivery-related phenomenon. One mechanism may be increased tumour pressure before therapy, which compresses immature central capillaries, with increased uptake post therapy due to redistribution of blood flow to the viable central vasculature because of reduction in interstitial pressure. If uptake in tumours is analogous to drug delivery, then pretherapy non-enhancing central volumes in MRI and PET may indicate that chemotherapy is not delivered initially to viable tumour centres. We hypothesise that drug delivery to the tumour centre may have improved after therapy in this patient, which has serious implications for decisions regarding extension of chemotherapy regimens in patients with this imaging characteristic.