Eble JN, Sauter G., Epstein JI, Sesterhenn IA - iarc

Congenital mesoblastic nephroma
P. Argani
P.H.B. Sorensen
Definition
Congenital mesoblastic nephroma
(CMN) is a low-grade fibroblastic sarcoma
of the infantile kidney and renal sinus.
ICD-O code 8960/1
Clinical features
CMN comprises two percent of paediatric
renal tumours {193,1845}. CMN is
the most common congenital renal neoplasm,
and ninety percent of cases occur
in the first year of life. The typical presentation
is that of an abdominal mass.
Macroscopy
Classic CMN has a firm, whorled texture,
while cellular CMN are more typically
soft, cystic and haemorrhagic.
{1377,2063,2338}. Cellular CMN but not
classic CMN demonstrates a specific chromosome
translocation, t(12;15)(p13;q25),
which results in a fusion of the ETV6 and
NTRK3 genes {1336,2255}. Interestingly,
the same chromosome translocation and
gene fusion present in cellular CMN was
first identified in infantile fibrosarcoma, and
is not present in infantile fibromatosis
{1337}. Hence, the analogy between cellular
CMN and infantile fibrosarcoma, and
between classic CMN and infantile fibromatosis,
appears appropriate.
The oncogenic mechanism of the ETV6-
NTRK3 gene fusion remains to be determined.
ETV6 is an ETS transcription factor
previously implicated in translocations
in paediatric B-cell acute lymphoblastic
leukaemia. NTRK3 is a tyrosine
kinase receptor that responds to
extracellular signals. ETV6-NTRK3 fusion
transcripts encode a chimeric protein in
which the sterile-alpha-motif (SAM) protein
dimerization domain of the ETV6
Histopathology
Classic CMN (24% of cases) is morphologically
identical to infantile fibromatosis
of the renal sinus {265}. Tumours are
composed of interlacing fascicles of
fibroblastic cells with thin tapered nuclei,
pink cytoplasm, low mitotic activity, and
an abundant collagen deposition. The
tumour dissects and entraps islands of
renal parenchyma. Cellular CMN (66% of
cases) is morphologically identical to
infantile fibrosarcoma. These tumours
have a pushing border, and are composed
of poorly formed fascicles, which
give way to sheet-like growth patterns.
The tumour shows a high mitotic rate,
and frequently features necrosis. Mixed
CMN (10% of cases) has features of both
classic and cellular CMN within the same
tumour.
A
Fig. 1.88 A, B Congenital mesoblastic nephroma, cellular type.
B
Immunoprofile
These tumours are immunoreactive for
vimentin and often actin with desmin
reactivity being rare and CD34 being
absent. Ultrastructurally, tumours have
features of myofibroblasts or fibroblasts.
Somatic genetics
While classic CMNs are typically diploid,
cellular CMNs frequently feature aneuploidy
of chromosomes 11, 8, and 17
Fig. 1.89 Congenital mesoblastic nephroma, cellular type. Note haemangiopericytomatous vascular pattern,
high cellularity and ill-defined fascicles.
60 Tumours of the kidney