[Does Bolande's malignant tumor exist?]

Congenital mesoblastic nephroma (CMN) is a rare renal neoplasm which Bolande differentiated from Wilms tumour given its benign nature. We describe 7 cases of CMN which have been treated over the last ten years, in order to highlight to what extent a tumour which is generally considered to be benign can have an aggressive behaviour. 5 patients were diagnosed during their neonatal period (3 of them prenatally) and 2 after the third month of life. Clinical presentation, simple abdominal radiology, echography and abdominal CT scan, which showed characteristic images, led us to a final diagnosis. Tumoral resection was carried out in the 6 typical CMN. The atypical or aggressive CMN was urgently operated under critical circumstances due to spontaneous tumoral rupture. The pathological study showed a CMN of cellular variety with a sarcomatous component. Despite adjuvant chemotherapy, there was a tumoral recurrence which required a surgical second-look and subsequent chemotherapeutical treatment. Bolande's tumour is generally benign, but there is an aggressive cellular variant that fits into the intermediate zone of a pathological spectrum. This aggressive variant have different clinical, radiological and anatomo-pathological features and therefore it involves radical surgical treatment and additional chemotherapy with a rigorous follow-up in the short and the long term.