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

of this tumour. Microscopic extension into
perinephric adipose tissue may be seen
infrequently {1584} and vascular invasion
has been described {77,563,2050}.
Since oncocytomas are benign neoplasms,
grading is not performed. There
is no diffuse cytoplasmic Hale’s colloidal
iron staining in oncocytomas.
Oncocytosis (Oncocytomatosis)
Several cases have been reported in
which the kidneys have contained a
large number of oncocytic lesions with a
spectrum of morphologic features,
including oncocytic tumours, oncocytic
change in benign tubules, microcysts
lined by oncocytic cells and clusters of
oncocytes within the renal interstitium
{1181,2618,2782}. The oncocytic nodules
usually have the morphologic and
ultrastructural features of oncocytoma
although some may have either chromophobe
or hybrid features.
Ultrastructure
Through ultrastructural examination,
renal oncocytoma is characterized by
cells containing numerous mitochondria,
the majority of which are of normal size
and shape, though pleomorphic forms
are rarely seen {722,2617}. Other cytoplasmic
organelles are sparse and unremarkable.
Notably absent are the
microvesicles typical of chromophobe
tumours.
Somatic genetics
Most renal oncocytomas display a mixed
population of cells with normal and abnormal
karyotypes {1376,1378}. In a few oncocytomas,
translocation of t(5;11)(q35;q13)
was detected {513,826,1376,2108,2687}.
Some of the cases show loss of chromosome
1 and 14 {1079,2108}.
Prognosis and predictive factors
Renal oncocytomas are benign neoplasms.
This conclusion is based largely
on the data from several recent studies
including rigorous pathologic review and
adequate clinical follow-up in which not a
single case of oncocytoma resulted in
the death of a patient due to metastatic
disease {77,563}.
Renal cell carcinoma, unclassified
J.N. Eble
ICD-O code 8312/3
Renal cell carcinoma, unclassified is a
diagnostic category to which renal carcinomas
should be assigned when they do
not fit readily into one of the other categories
{1370,2514}. In surgical series,
this group often amounts to 4-5% of
cases. Since this category must contain
tumours with varied appearances and
genetic lesions, it cannot be defined in a
limiting way. However, examples of features,
which might place a carcinoma in
this category include: apparent composites
of recognized types, sarcomatoid
morphology without recognizable epithelial
elements, mucin production, mixtures
of epithelial and stromal elements, and
unrecognizable cell types.
Sarcomatoid change has been found to
arise in all of the types of carcinoma in
the classification, as well as in urothelial
carcinoma of the renal pelvic mucosa.
Since there is no evidence that renal
tumours arise de novo as sarcomatoid
carcinomas, it is not viewed as a type of
its own, but rather as a manifestation of
high grade carcinoma of the type from
which it arose. Occasionally, the sarcomatoid
elements overgrow the
antecedent carcinoma to the extent that
it cannot be recognized; such tumours
are appropriately assigned to renal cell
carcinoma, unclassified.
Oncocytoma / Renal cell carcinoma, unclassified
43