35
Immunocytochemistry
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F ig . 3 5 .4
(a) Antibody to
s o m a to s ta tin
is negative in this smooth muscle tumor, whereas the same slide subjected to antibodies to
H H F -3 5 m u s c le a c tin
shows strong immunostaining (B). (C) This aspirate of a large-cell tumor had been negative for
C A M 5 .2 ,
but when subjected to antibody to
le u k o c y te
c o m m o n a n tig e n ,
strong membrane staining was seen, confirming the diagnosis of
m a lig n a n t ly m p h o m a , la rg e -c e ll ty p e .
In th is technique, cells are lifte d o ff o f a slide b y redissolving
th em in a new m o u n tin g m ed ium . The m ed ium can be rem oved
fro m the slide, cut in to pieces, and reapplied to slides fo r in d i-
vid u al a ntib od y studies (Fig. 3 5.5). The results o f im m u n o -
stains are generally good, a lthoug h H u n t and colleagues have
described som e decreased staining w ith th is m eth od .30
Interpretation and Limitations of ICC
As in surgical p athology, the m o rp h o lo g ic stud y o f th e speci-
m en in concert w ith th e c lin ic o p a th o lo g ic c orrelations is o f
p a ra m o u n t im p o rtan ce in a rriv in g at a correct diagnosis. N o
a m o u n t o f im m u n o s ta in in g w ill a ffo rd a correct diagnosis
w ith o u t a th o ro u g h p a tie n t w o rk u p o r tissue e xa m in ation .
O n ly w h e n im m u n o s ta in in g find ing s are com b ined w ith c lin i-
cal and o th e r a n c illa ry data is a p a tie n t w o rk u p considered
com plete.
There is a p le th o ra o f a ntib od ies th a t are available fo r use in
cytology, and n o n e o f th e m is specific fo r its intend ed target.
A ntib o d ie s m ay be p o lyc lo n a l o r m o n o c lo n a l, vary in sen sitiv-
ity and specificity, o r m ay be dependent o n certain types o f
fixative fo r p rop er im m u n o re a c tivity . In a d d itio n , th e d iffe r-
e n tia tio n o f m an y tu m o rs e xh ib its a w id e spectrum . For these
reasons, it is im p o rta n t to use k n o w n p o sitive and negative
c on trols w ith a panel o f m u ltip le antib od ies th a t are k n o w n
to be p o sitive and negative in th e cytologic study. A negative
re su lt b y its e lf is o f lesser value th a n a p o sitive result, unless
th e cytolog y specim en its e lf contains k n o w n p o sitive and
negative c o n tro l cells.
The pattern o f im m u n o s ta in in g w ill depend o n the presence
o f neoplastic cells; the lo c a tio n of, fo r example, cell m em brane,
cytoplasm , o r nucleus; proper fix a tio n ; background staining;
and a ntib od y concentration. Im m u n o s ta in in g fo r any antigen
is rarely u n ifo rm in nature. H eterog eneity o f im m u n o s ta in in g
is the ru le rather th a n the exception, and it is proper to state
the pattern, cell loc aliza tio n , and d istrib u tio n o f p ositive and
negative im m u n o s ta in in g relative to n o rm a l cells th a t m ay be
present in the sample.
False-positive im m u n o s ta in in g results can be a result o f a
m u ltitu d e o f factors. First and forem ost, the cytop atholog ist
m ust n o t m istake n o rm a l cellular elem ents fo r neoplastic cells,
especially in samples in w h ic h neoplastic cells are few. The same
caution applies to reactive cells in the sample. D ry in g the slide
d uring any step in the im m unop eroxid ase procedure results
in nonspecific a ntib od y b in d in g th a t can be m isinterp reted
as p ositive findings. Necrotic, p o o rly preserved, and crushed
cells m ust be avoided because nonspecific b in d in g m ay yie ld
a false-positive result. Care m ust be taken n o t to overinterp ret
the hig h er background th a t is generally seen w ith p olyclonal
1049
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