Diagnostic Cytology
• T he le io m y o m a to u s c o m p o n e n t m a y com p rise sp in d le o r
ro u n d cells w ith g ra n u la r c ytop lasm ; and
• T he le io m y o m a to u s c o m p o n e n t is p o sitiv e fo r s m o o th
m uscle a c tin and m e la n o m a m arkers such as H M B -4 5 and
m e la n A (A 103).
Benign Epithelial Tumors
O ncocytom as are composed o f oncocytes, w h ic h are large epi-
th e lia l cells w ith abundant eosinop hilic cytoplasm . O ncocyto-
mas were o rig in a lly id entified b y H am p erl in the salivary gland
in 1931 37-38 and were previously recognized in the th yro id and
parathyroid. They were recognized in the kidneys in 1976, w hen
K lein and Valensi39 reported on 14 patients w ith oncocytic tum ors
and emphasized th e ir benign behavior. These tum ors are regarded
as variants o f renal adenomas, derived m ost lik e ly fro m the m ito -
chondria-rich principal cells o f collecting duct o f m ed ullary ori-
g in.13,40 A ltho ug h they m ay become large, they generally show no
tendency to invade o r metastasize. The reported average incidence
is 5% o f a ll renal neoplasms; they occur p red o m in an tly in m en,
w ith a peak incidence in the sixth to eighth decades o f life .20
T he gross features o f th is neoplasm are characteristic; they
includ e a w ell-dem arcated, w ell-encapsulated tu m o r th a t is a
m ahogany c olor o r reddish b ro w n o n the cut surface. The tum ors
range in size fro m several m illim e te rs to 25 cm in diam eter, w ith
a m edian diam eter o f 8 cm. A central fib rous scar is o fte n seen.
Tum ors are u su ally solitary; however, th ey m ay be b ilateral o r
m ulticentric.
T he tu m o r m ay be com posed o f nests o r cords o f oncocytic
cells separated b y edem atous strom a. Typical cells are p o ly-
gonal, w ith ro u n d o r oval, hyp erchrom atic nuclei and m in im a l
p leo m o rp hism (Fig. 2 7.4).20 Binucleated cells m ay fre q ue ntly be
seen. Lieber and colleagues described six cases th a t m etastasized
and led to the u ltim a te dem ise o f the patients.41 These tum ors
were characterized by nuclei th a t showed greater nuclear pleo-
m orp h ism th a n in the usual oncocytom a.
Fig. 27.4 Oncocytoma showing single cell pattern with well-defined sharp
borders, abundant dense granular chromatin, and small round eccentrically
placed nuclei that are occasionally densely hyperchromatic (arrow) but
usually have small nucleoli (Papanicolaou x MP).
A m o n o to n o u s p o p u la tio n o f polyg onal single cells o r sm all
clusters o f cells w ith defined cell borders is seen, as w e ll as abun-
d ant e osin o p hilic cytoplasm . N uclei are ro u n d to oval, single o r
m u ltip le , and hyp erchrom atic o r so clum ped th a t they appear
p yknotic (Fig. 2 7.5).
O ncocytom a m ay be confused w ith a g ran u la r cell RCC and
a chrom o p ho b e cell renal carcinom a (C C RC ) (discussed later).
D is tin g u is h in g features in fa vor o f oncocytom a includ e con-
siste n tly densely g ran u la r e o s in o p h ilic cytoplasm in a ll cells,
in contrast to th e e o s in o p h ilic v a ria n t o f CCRC, w h ic h shows
rare clear cells w ith reticulated cytoplasm and p ositive sta in in g
o n H ale's c o llo id a l iro n . O ncocytom as are o f lo w nuclear grade
and u su a lly d ip lo id .42 G ran ula r RCC u su a lly has h ig h e r grade
nuclei w ith p ro m in e n t n u c le o li. It m ay sho w focal areas o f
clear cells and m ay be a n e u p lo id .42 Cytogenetics m ay be h e lp -
fu l to d iffe re n tia te oncocytom a fro m RCC, because th e fo rm e r
has n o d e le tio n o f c hrom osom e 3p (in contrast to RCC) and
is u su a lly a m osaic o f n o rm a l karyotyp e and a b no rm a l clones
(Table 2 7 .2 ). O ncocytom a has n o consistent karyotyp ic a b no r-
m a lity .43 A d istin ctive restrictive p attern o f m ito c h o n d ria l D N A
has been fo u n d in oncocytom as.43 In a d d itio n , oncocytom a
contains an a n io n exchange p rotein, also k n o w n as band 3
p ro te in .44
Im m unocytochem istry
oncocytom as
im m u n o p o s itiv ity fo r parvalbu-
m in , Ksp cadherin, and C -k it.45 T his im u n o p ro file is s im ila r to
chrom op hob e RCC. However, CK-7 shows a d iffe re n tia l staining
pattern between chrom op hob e RCC and oncocytom as. In con-
trast to chrom op hob e RCC, in w h ic h CK-7 expression is noted
in 5 0 -1 0 0 % o f cases w ith a distinctive m em brane accentuation,
oncocytom as show o n ly focal cytoplasm ic staining occasionally
in 8% o f cases.
Key features of oncocytoma
• B en ig n tu m o r com p osed o f o nc oc ytic cells;
• A b u n d a n t g ra n u la r e o s in o p h ilic cytop lasm ;
Fig. 27.5 Oncocytoma. Histologic section showing cells with dense
eosinophilic cytoplasm and regular euchromatic nuclei with central small
nucleoli, arranged in nests (H&E x MP).
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