Congenital mesoblastic nephroma (CMN) with an unusual immunohistochemical feature

To describe a case of congenital mesoblastic nephroma (CMN) treated by radical nephrectomy with no evidence of relapses after five years in spite of an unusual positivity for proliferating cellular nuclear antigen (PCNA).

A three-month-old child presented a right renal mass with compression of the inferior vena cava. Excretory urography showed an intrarenal mass with distortion of the calyceal system. There was no evidence of metastasis. Radical nephrectomy was carried out; no adjuvant therapy was given. Histological and immunohistochemical studies were performed.

The tumor was a 6 x 6 x 5 cm solitary mass extending into perirenal tissue, involving the hilar vessels but not the ureter. Histologically, it has been classified as a congenital mesoblastic nephroma of the classic variant. Positive reaction for vimentin and actin was observed. Strong positivity for PCNA and negativity for P53 were revealed.

PCNA is considered to be a reliable marker of potential malignancy. This, however, contrasts with the biological behavior of our case. Further evaluation is required for correct interpretation of this additional information and to avoid inappropriate aggressive therapy.