Primary renal osteosarcoma: a very rare tumour with an ominous prognosis
Primary renal osteosarcoma is very rare and fatal sarcoma of the kidney, as of 2015, has only been described in 30 cases in the world literature.1 Histogenesis is still unclear; the metaplastic reversion of connective tissue into primitive mesenchyme with osteoblastic potential is the most plausible theory. Histologically, it consists of abundant osteoid stroma generated by the proliferative cancerous cells. Prognosis is poor. Most patients become symptomatic only at an advanced stage and die of distant metastases within 8–15 months from the diagnosis (23 cases), whereas a disease‐free survival is occasional (only two cases).1 Surgery, chemotherapy and radiotherapy are often palliative. Resection is curative only in the case of early detection of small tumours.1 A palpable abdominal mass, flank pain and gross hematuria are the most common clinical manifestations. Of interest, an intestinal subocclusion secondary to neoplastic involvement of the colon has been described only in two instances so far.2 Elevated serum levels of alkaline phosphatase may facilitate the diagnosis and the detection of recurrences or metastases during the follow‐up. A cogent help to suspect such an infrequent tumour seems to be furnished by the so‐called sunburst sign detectable within the renal contours on plain abdominal X‐ray. This feature was present in 11 cases and in one instance it anticipated the final diagnosis 2 years in advance.