Si es un nefroma, como muy bien ha deducido Laura, te he encontrado esta definición en
www.mercksource.com:
nephroma (ne·phro·ma) (n[schwa]-fro¢m[schwa]) [nephr- + -oma] a tumor of the kidney or of kidney tissue.
congenital mesoblastic nephroma, a renal tumor similar to Wilms' tumor but appearing earlier in infancy and with more infiltration of surrounding tissue than in classic Wilms' tumor.
embryonal nephroma, Wilms' tumor.
Un saludito, ¡y que te mejores!
EVA.