Secretion of a large molecular-weight form of insulin-like growth factor by a primary renal tumor.

A 5-year-old boy with an abdominal mass was found to have a primary renal tumor of poorly identifiable histology. Prior to resection of the tumor, the patient exhibited several episodes of biochemical hypoglycemia. The hypoglycemia did not recur after operation. Analysis of tumor tissue and of pre- and post-operative sera by column chromatography showed elevated insulin-like growth factor II (IGF-II) levels in the tumor; an abnormal large-molecular weight precursor form of IGF-II (pro-IGF-II) comprised 53% of total IGF-II in the tumor and 42% in preoperative serum. No pro-IGF-II was found in the serum 6 weeks post-operatively. Abnormal IGF-II secreted by the tumor may have mediated the hypoglycemia seen prior to tumor resection. This pediatric renal tumor is the first to our knowledge for which an association of non-islet cell tumor-related hypoglycemia and elevated tumor IGF-II content has been described.