INVESTIGATIVE OPHTHALMOLOGY
November 1972 Volume 11, Number 11
Ultrastructural comparison of spindle A,
spindle B, and epithelioid-type cells
in uveal malignant melanoma
Takeo Iwamoto, Ira Snow Jones, and George M. Howard
Eight cases of uveal malignant melanoma were studied with the electron microscope with
the purpose of comparing the ultrastructural features of the three basic cell types (spindle
A, spindle B, and epithelioid) originally described by Callender under the light microscope.
Five of the eight tumors were of pure cell type, and three were mixed. This was undertaken
because of earlier diverse opinions regarding the ultrastructure of those cell types based
mainly on studies of spindle B, epithelioid and mixed-type melanomas. In the five melanomas
of pure cell type (one spindle A, two spindle B, and two epithelioid), the following tendencies
characterizing each cell type were found: The size and the degree of reticulation of nucleoli
and the number of free ribosomes and mitochondria increased from spindle A to spindle
B and epithelioid cells, while rough-surfaced endoplasmic reticulum was most prominent
in the spindle B type. On the other hand, cytoplasmic filaments decreased in the same order.
There were also other minor differences. The ultrastructural details of these are described
and their significance is discussed. Judging from the behavior of nucleoli and free ribosomes,
the results were consistent with the present consensus that the cellular malignancy increases
from spindle A through spindle B to epithelioid-type cells. In mixed-type melanomas, the
celhdar features were often more complicated because of structural variations and the presence of cells which could be regarded as intermediates.
Key words: ultrastructure, uveal tract, malignant melanoma, pathology, neoplasm,
cell types, nucleolus.
M
pie. 1 ' 2 In light microscopy, Callender3'5
classified these tumors into six different
cellular types, i.e., spindle A, spindle B,
fascicular, epithelioid, mixed, and necrotic.
Of these, the basic cell types are spindle
A, spindle B, and epithelioid while the
other types can be regarded as a combination of these or a modification. This cellular
classification has contributed to morphology and also, because of its relation with
clinical prognosis, to estimating cellular
malignancy; the degree of malignancy increases in the order of spindle A, B, and
epithelioid.1'5
alignant melanomas of the uveal tract
are one of the common neoplasms of the
eye, particularly among Caucasian peo-
From the Department of Ophthalmology, College
of Physicians & Surgeons of Columbia University, 635 W. 165th St., New York, N. Y. 10032.
This investigation was supported by Public Health
Service Research Grant No. EY-00190-16 from
the National Eye Institute, and a grant from
the Zelda Radow Weintraub Cancer Fund, Inc.
Manuscript submitted Aug. 24, 1972; manuscript
accepted Sept. 15, 1972.
873
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874 Itoamoto, Jones, and Howard
There have been many electron microscopy studies on the uveal malignant
melanomas,0"20 and an attempt to disclose
the ultrastructural characteristics of these
•classical cell types has also been made.
"While some authors14 did not find any
features specifying the cell types, others12
5aw a uniform ultrastructure of the tumor
cells in each of their mixed-type melanomas
•with some structural differences between
the cells of the different tumors. The fine
structure of spindle B and epithelioid-type
cells has been described in detail by
.several authors.0' T> Oi 10' ri> 18> 24 However,
there have been significant differences in
their observations, particularly in regard to
the number of rough-surfaced endoplasmic
jeticulum (RER) and free ribosomes. Relatively, few reports have appeared on
.spindle A type. Some melanomas thought
to be spindle A in preliminary light microscopy were found to be largely spindle B
by subsequent electron microscopy because
of the presence of nucleoli,0'1G and one
article dealing with this type stated that
the cells had a well-developed nucleous,20
giving the impression of possible spindle B
type. Other authors20 described the spindle
A cells relatively briefly, and these simulated normal uveal melanocytes including
the pigment granules; in another spindle A
melanoma25 the tumor cells were surrounded by many axon-like structures. Our
recent study on the spindle A type in a
case of "tapioca melanoma," a peculiar type
of malignant melanoma of the iris, showed
the cells to have similarities to normal iris
melanocytes as well as differences, the
latter including the pigment granules which
were largely premelanosomes with granular
elements.27
To our knowledge, detailed ultrastructural comparisons have not been made in
the three basic cell types of Callender's
classification; this is particularly true in
regard to the nucleolus and cytoplasmic
filaments. The main purpose of this paper
is to compare the cellular fine structure of
these classical cell-types in our selected
cases of uveal malignant melanomas where-
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Investigative Ophthalmology
November 1972
in the tumors were composed of an almost
pure single-cell type. Other cases of mixedtype melanomas are also included in this
study.
Materials, methods and light microscopy
Eight cases of uveal malignant melanoma (age
47 to 77, all Caucasian) were selected from our
collection of more than 30 cases. All the tumor
tissues studied were obtained surgically, either
by enucleation or iridocycletomy. Immediately
after the enucleation, the eyes were cut into
halves anteroposteriorly through the tumors, which
had been located by transillumination, and one
half was fixed in 10 per cent formalin and embedded in paraffin for routine light microscopy.
The other half was prepared for electron microscopy following the procedures reported elsewhere28: They were fixed with 3 to 4 per cent
glutaraldehyde in 0.05M phosphate buffer (pH
7.4), postfixed with 1 per cent Osd, dehydrated in graded alcohols, and embedded in resin
(Durcupan ACM). First, 1/* sections were
cut and stained with Giemsa stain for light
microscopy. Subsequent thin sections were stained
with uranyl acetate and lead citrate for electron
microscopy. Tumors obtained by irridocyclectomy
were immediately divided into halves, and processed by the same method. The Porter-Blum
microtome was used for sectioning, and the
Zeiss EM-9S for electron microscopy.
Light microscopy of the routine paraffin sections and of the lfi thick, resin sections revealed
all the tumors to be malignant melanomas (MM)
of the uveal tract with cellular features as follows :
Tumor No. 1. MM of choroid composed of
apparently nonpigmented spindle A-type cells;
the cells were spindle shaped in longitudinal
sections, and the nuclei showed delicate chromatin and ill-defined nucleoli, as seen in paraffinsections (Fig. 1, B). However, resin-embedded
sections revealed these spindle A cells to contain
clear nucleoli which were much smaller than
those of spindle B and epithelioid cells (Fig.
1, A).
Tumors Nos. 2 and 3. MM of choroid (No. 2)
and iris and ciliary body (No. 3). Both showed
essentially the same cellular structure composed
of lightly pigmented spindle B-type cells; the
spindle-shaped cells possessed nuclei with a coarse
chromatin pattern and large clear nucleoli (Fig.
1, C). Heavily pigmented cells, some appearing
to be macrophages, were scattered among these
cells; however, the election microscopy (EM)
studies were confined to the regions with lightly
pigmented, typical spindle B cells.
Tumors Nos. 4 and 5. Both were MM of
choroid, having essentially the same cellular fea-
Yolnmr I 1
Vltrastniclural comparisons in malignant melanoma S75
KIIIIII.IT ! I
Fig. i. Light inicrographs ot three basic cell types ot uveal malignant melanomas. »H4U. .\
and B. Spindle A-type cells (tumor No. 1). Small nucleoli (arrow) are visible in resin-sections
(.A), while they are ill-defined in paraffin-sections (B). C and D. Spindle B (tumor No. 2)
and epithe!ioid-t\ pe cells (tumor No. 4), respectively.
lures. Tlie central bulk of the tumors consisted
of nonpigmented epithelioid-tvpe cells; the cells
were round or polygonal with large rounded
nuclei containing prominent nucleoli (Fig. 1, D).
A few spindle-shaped cells were found in the
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periphery of both tumors; the KM study was
confined to the central bulk regions with almost
pure epithelioid-type cells.
Tumors Nos. 6, 7, and 8. MM of choroid (Nos.
6 and 8) and of iris and ciliary body (No. 7).
876 Iwamoto, Jones, and Howard
All were mixed types of spindle B and epithelioid.
While No. 7 was almost nonpigmented, Nos.
6 and 8 contained varying numbers of heavily
pigmented cells in the tumor periphery; EM of
the latter tumors was confined to the central
bulk regions with lightly pigmented cells.
Results
Spindle A-type cells. Electron microscopy
of the spindle A-type cells in tumor No.
1 revealed the following. The cells were of
an elongated spindle shape in longitudinal
sections, and irregularly rounded in crosssections. The nuclei in the middle of the
cell bodies also were elongated or rounded,
following the cellular contours (Fig. 2, A).
The nuclear surface often showed marked
indentations, some of them oriented
longitudinally along the nuclear long axis
(Fig. 2, B). The nuclear chromatin was
dispersed in most cells, with a thin layer
of condensed chromatin at the nuclear
periphery (Fig. 2, B). There were one to
several small nucleoli (average lju. in
diameter) in the nucleus (Fig. 2, B), and
at higher power each nucleolus was composed of a peripheral granular component
and a central fibrillar component. The
fibrillar component which usually contained
a rounded less dense zone (fibrillar center)29
in the cental portion showed little or no
tendency to form a network pattern or reticulation. Most of the granular component
surrounding the fibrillar appeared to be
nucleolus-associated chromatin (200 to 250
A in diameter), and some of the granules
were superimposed on the fibrillar component (Fig. 3, B).
In the cytoplasm, there were a moderate
number of mitochondria, usually uncharacteristic but often elongated along the
cellular long axis, a relatively small number
of free ribosomes which were mostly of a
clustered form or polysomes, a few short
segments of rough-surfaced endoplasmic reticulum (RER), and numerous cytoplasmic
filaments (Figs. 2, B and 3, A). Occasionally one or more groups of elongated
cisternae of RER arranged in parallel were
also found. Large Golgi complexes often
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Investigative Ophthalmology
November 1972
accompanied with coated vesicles, centrioles, a short cilium, microtubules,
smooth-surfaced endoplasmic reticulum
(SER) of tubular, vesicular of larger
vacuolar forms (Figs. 2, B and 3, A), and
lipid-like inclusions (such as in Fig. 4, B)
were also present. Pinocytotic vesicles were
numerous near the cell surface (Fig. 3, A).
Pigment granules were few in most cells,
and largely immature melanin granules
(or premelanosomes)30 which were either
nonmelanized or lightly melanized (see
Discussion).
In addition to these usual cells with a
relatively light cytoplasm, there were few
cells with a darker cytoplasm (Fig. 3, C).
These cells appeared to have resulted from
a simple condensation of the cellular constituents of the lighter cells; some such
cells seemed degenerated with irregular
vacuoles.
Spindle B-type cells. Electron microscopy
of the spindle B-type cells in tumors Nos. 2
and 3 showed essentially the same ultrastructural features. The shape of the cells
and nuclei was similar to that of spindle
A-type cells, but the cell bodies were generally plumper than the latter (Fig. 4, A).
The nuclei showed marked indentations of
the nuclear surface, and in many cells the
nuclear chromatin tended to form irregular
clumps beneath the nuclear membrane as
well as in central nuclear portions (Fig. 4,
A, and B). The nucleoli were much larger
(average 2 JX in diameter) than those of
spindle A, and showed a marked network
pattern (Fig. 4, A). When compared with
the nucleoli of epithelioid-type cells, the
size was often smaller in spindle B-type;
however, since their ultrastructure was essentially the same in both types, the detail
is described in the epithelioid-type cells. In
the cytoplasm, there were many, usually
uncharacteristic mitochondria, some of
which were markedly elongated along the
cellular long axis (Fig. 4, A). Free ribosomes were numerous, and composed of
both polysomes and monosomes (Fig. 5, A,
and C). Although the number varied from
UHrastructural comparisons in malignant melanoma
Volume 11
Sum bet 11
II;
'.
1C
Fig. 2. (Figs. 2 to 9 are electron micrographs, the line in each figure representing In unless
otherwise indicated). Spindle A-type cells (tumor No. 1). A. Low power view. Cells are
spindle-shaped with oval nuclei ( n ) in longitudinal sections, m = mitochondria x5,040. B.
Higher power of a spindle A-type cell. The nucleus with a small nucleulus (nl) has a
longitudinal invagination (arrow); chromatin is dispersed. Mitochondria ( m ) , short segments
of RER ( r e ) , a Golgi complex ( g ) , and centrioles ( c ) are in the cytoplasm, ev — coated
vesicels (for higher power, see Fig. 4; inset), p = premelanosome (for higher power, see Fig.
9, A ) , x 12,350. Inset: cross-section of a cilium in spindle A cell. >58,400.
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877
Investigative Ophthalmology
November 1972
878 Iuamoto, ]ones. and Howard
<• se
. • mi
B
X
Fig. 3. Spindle A-t\pe cells. A. Cxtoplasmic portions, showing a few short segments o: RER
(re) and free ribosonies (mostly polysomes) ( r ) , and numerous eytoplasmie filaments ( f ) .
nit " inierotiibules, se ~ SKR of vesicular form, pv = pinoe\totic \esicles <31,200. B. Higher
power of a spindle A micleous. The fihrillar component (f) with a fihrillar center (fc) shows little
tendency ol network formation, (•ranular component ( g ) surrouds the h'l)rillar, and partial
superiinposition of the two components are seen at ( s ) . >54,000. C. A dense cell, appearing
to lie a simple condensation of a usual lighter cell, f = filaments, r = free rihosomes, arrow =
desmosome-like structure between a dense and a lighter cell "54.000.
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Ultrastrttctural comparisons in malignant melanoma 879
1
CV
Fig. 4. Spindle B-tvpe cells (tumors Xos. 2 and 3 ) . A. Low power of a spindle B-t\ pe cell
in longitudinal section. Oval nucleus with clumped chromatin has a large reticulated nn.leolus
( n l ) . Many mitochondria (in) and preinelanosomes (p) (for higher power, see Fig. 9, B and C)
are in the cytoplasm. • 9,975. K. Higher power of another cell. Indented nucleus shows clumps
of condensed chromatin tc). m = nn'tochondria. g -'~ C.olgi complex, re = elongated RF.R.
f = bundled filaments, 1 ^^ lipid-like inclusion; this can lie seen in other cell tvpcs also.
•16,8(K). Inset: Higher power of a squared portion in li, showing coated vesicles ( c v ) . -<32.00U.
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880 Iwamoto, Jones, and Howard
cell to cell, RER was well developed in
many cells; both short segments and
elongated forms were present, but the
latter predominated. Usually each cisterna
of the elongated RER was irregularly
curved and dispersed in the cytoplasm
(Fig. 5, A); sometimes such cisternae were
arranged concentrically,7'9 and occasionally
fragmented cytoplasmic portions were
found within a rounded RER-cisterna (Fig.
5, B). Cytoplasmic filaments were fairly
numerous (Fig. 5, C), but appeared less
prominent than those of spindle A-type
cells. These filaments tended to form bundles (Fig. 4, B). A few small cytoplasmic
processes could be seen on the cell surface.
Golgi complexes were often large, and
there were also coated vesicles, centrioles,
microtubules, lipid-like inclusions (Fig. 4,
B), SER, and pinocy totic vesicles. Pigment granules were fairly numerous in both
tumors, and they were largely premelanosomes (see Discussion).
Epiihelioid-type cells. Electron microscopy of the epithelioid-type cells in tumors Nos. 4 and 5 showed rounded or polygonal cells with large rounded nuclei (Fig.
6, A). There were indentations of the nuclear surface, but they appeared less prominent than those of spindle A and B-type
cells. The chromatin was dispersed with a
thin condensed layer beneath the nuclear
membrane, and the rounded nucleoli were
often larger than those of spindle B-type
cells (2 to 3 ix in diameter) (Fig. 6, A,
and B). At higher power, the ultrastructure
of the nucleolus was essentially the same
as in spindle B-type cells. Generally, it consisted mainly of a fibrillar component
which formed a prominent network or
reticulation; one to several less dense
rounded zones (or fibrillar centers) were
distinguishable within the reticulated fibrillar component. The granular component
was mostly superimposed on the fibrillar,
the granule size varying from 250 to 100 A
in diameter (many were 150 A) (Fig.
7, A). In the cytoplasm, there were numerous mitochondria, which in one tumor
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Investigative Ophthalmology
November 1972
(No. 4) were mostly noncharacteristic
(Fig. 6, B) and in the other (No. 5) often
showed a bizarre form and structure (Fig.
7, E). Free ribosomes were very numerous
and largely monosomes (Fig. 7, B). Usually, short segments of RER were dispersed
in the cytoplasm, some possessing only a
few attached ribosomes (Fig. 7, B; occasionally, a few elongated cisternae of
RER were also found at the peripheral portions of the cytoplasm. Cytoplasmic filaments were the least prominent among
three cell types (Fig. 7, B). As in the other
type cells, well-developed Golgi complexes, centrioles (occasionally a short
cilium as well), coated vesicles, microtubules, and SER as well as pinocytotic
vesicles were present. Pigment granules
were few in one tumor (No. 4) and fairly
many in the other (No. 5), and in both
they were mostly premelanosomes (see Discussion); some premelanosomes of tumor
No. 5 simulated lysosomes. Thin cytoplasmic processes on the cell surface were
prominent in both tumors (Fig. 7, D). In
addition to these usual cells with a relatively light cytoplasm, some cells possessed
a darker cytoplasma. These appeared to be
a simple condensation of the lighter cells,
and often assumed a starshape probably
due to shrinkage; some such cells seemed
degenerative with vacuoles of irregular
shape (Fig. 7, C).
Mixed-type cells. Malignant melanomas
Nos. 6 and 7 were a mixed type of epithelioid cells and fewer spindle B-type cells;
No. 8 was made up predominantly of
spindle B with fewer epithelioid cells. Distinction of individual cell types was often
difficult in these tumors, partly because of
ultrastructural variations and partly due
to the presence of what appeared to be
intermediate cells. In these limited cases,
however, the structural features of typical
type cells, i.e., spindle B and epithelioid,
were consistent with the criteria made in
pure-type melanomas.
Ultrastructural variations were as follows: in one tumor (No. 6), epithelioid-
Volume 1 1
Sum her 11
Uhrastructural comparisons in malignant melanoma 881
Fig. 5. Spindle B-type cells. A. Cytoplasm with numerous free ribosomes ( r ) and prominent
RER of elongated from ( r e ) , n = nucleus, m = mitochondria, x27,200. B. Concentrically arranged RER ( a ) and a RER-cisterna containing fragments of cytoplasm ( b ) . x23,200. C.
Higher power of cytoplasm, showing free rebosomes ( p = polysomes, m = monosomes) and
scattered filaments ( f ) . x42,480.
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i Ophthalmology
Smcmbcr 1972
Iwanwto. Jones, and Howard
• * « •
F i g . (). I'.pithelioid-tvpe cells ( t u m o r N o . 4). A. L o w p o w e r view. R o u n d e d or p o l y g o n a l cells
h a v e l a r g e r o u n d e d nuclei ( n ) w i t h l a r g e n u c l e o l i ( n l ) . * 6 , 4 8 0 . B. H i g h e r p o w e r of a n e p i t h e l i o i d - t y p e cell. .Nucleus ( n ) w i t h d i s p e r s e d c h r o m a t i n c o n t a i n s a l a r g e r e t i c u l a t e d n u d e o h i s
( n l ) . N u m e r o u s m i t o c h o n d r i a ( i n ) , a Golgi c o m p l e x ( g ) , a n d s h o r t - s e g m e n t s of R E R ( r e )
a r c \ i s i h l c in t h e c x t o p l a s m ; n u m e r o u s d o t s a r e t r e e ribosomt's. N 13.000.
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Vltrastructural comparisons in malignant melanoma 883
Fig. 7. Epithelioid-t\ pe cells. A. Higher power of a nuclcohis, showing the peripheral portion.
Khrillar components ( t ) form a marked network on which most granular component ( g ) is
superimposed, c — fibrillar center. <56,7()0. B. Higher power of a cvtoplasinic portion, showing
numerous free rihosomes (small dots). At arrow, short segments of KKR (or) appear to he
formed liy segregation of an originatl\ elongated HER; some HER has tew attached ribosomes
( o r ) . Cltoplasmic filaments are ver\ tew. see
smooth-surfaced endoplasmic reticnluin.
•2-1.000. C. A (l<'iise cell, appearing to lie a degenerating lighter cell. -16,800. D. Small c\ toplasmic processes ( p ) on cell surlace. • l(i.8()0. /•'. Bi//are mitochondria ( i n ) ; the shape,
si/e, and cristae are unusual. • Hi.800.
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Investigative Ophthalmology
November 1972
884 hoamoto, Jones, and Howard
Table I. Major features of three basic cell types in uveal malignant melanoma
Spindle A
Spindle B
Epithelioid
Small
Large
Large
(Polysomes)
(Polysomes and monosomes*)
(Monosomes*)
Nucleolus:
Reticulation
Ribosomes:
RER:
Short
Long
+
Mitochondria:
+
(Often bizarre)
Filaments:
+++
•In mixed type, sometimes polysomes.
type cells contained mitochondria with
prominent osmiophilic bodies, as observed
by others.13 Occasionally, annulate lamellae23 could be seen in the epithelioid-type
cells of this tumor. In another tumor (No.
7), numerous glycogen particles12'14 were
found in the cytoplasm of both spindle
B and epithelioid cells (Fig. 8, A); these
particles were also seen in the central portion of a concentrically arranged RER. In
still another tumor (No. 8), the elongated
RER of spindle B-type cells was very
prominent, and tended to form a parallel
arrangement. Also, numerous free ribosomes of both spindle B and epithelioid
cells were largely polysomes, and their distribution within the cytoplasm often appeared irregular.
An example of probable intermediate
cells is shown in Fig. 8, B (from tumor No.
8). The rounded cellular portion with the
nucleus shows features similar to the epithelioid type seen in pure-type melanomas,
whereas the remaining cytoplasmic extension with prominent RER of an elongated
form is suggestive of spindle B-type cell.
A multinucleated giant melanoma cell with
a similar intermediate-form could be found
in the same melanoma (Fig. 8, C).
Discussion
Despite numerous electron microscopy
studies on uveal malignant melanomas, the
fine structure of the different cell types
classified by Callender under the light
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microscope is still controversial. In our
studies on almost pure-type melanomas
also, the ultrastructural differences between
different cell types were not clear-cut ones.
However, there were certain tendencies
which seemed to characterize each of the
three basic cell types, i.e., spindle A, spindle B, and epithelioid. Major distinctive
features could be seen in the nucleoli,
ribosomes, rough-surfaced endoplasmic reticulum (RER), mitochondria, and cytoplasmic filaments, as listed in Table I.
The size of nucleoli increased in the
order of spindle A, spindle B, and epithelioid. In light microscopy of ordinary
paraffin sections, the nucleoli of spindle
A-type cells appeared ill-defined or absent.
However, with resin-embedded sections
there were clear nucleoli which were much
smaller than those of spindle B and epithelioid cells. In electron microscopy, these
nucleoli were characterized by small size
with little tendency to form a network pattern or reticulation of the fibrillar component, one of two main components of the
nucleolus.0 A fairly prominent granular
component, which appeared to be mainly
nucleolus-associated chromatin, surrounded
the fibrillar component; there was only a
partial superimposition of the two components. In spindle B and epithelioid cells,
•Of the four31 or five29 nucleolar constituents, two main
components, a fibrillar (about 50 A in diameter) and
a
granular (about 150 A in diameter), are well accepted.32' M
Our granular component includes "nucleolus-associated
chromatin" (200 to 250 A in diameter).33. 34
Volume 11
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Ultrastructural comparisons in malignant melanoma 885
the nucleolus was much larger, with a
markedly enlarged, reticulated fibrillar
component. The granular component was
mostly superimposed on the fibrillar component, with the granule size ranging from
chromatin size (200 to 250 A in diameter) 33 ' 35 to smaller ones; many granules
were about 150 A in diameter. Although
the nucleolar fine structure was essentially
the same in both spindle B and epithelioid,
the average size was larger in the latter
cells, mainly due to amore enlarged fibrillar region. Such a nucleolar hypertrophy is
commonly observed in various malignant
tumor cells.30 However, sequences of nucleolar enlargement similar to those in
melanoma cell nucleoli could also be seen
in our study of normal adult rabbit lens,
which led us to assume the participation
of chromatin in such an enlargement.33 Our
present observation was consistent with
this hypothesis.
Apparently the number of free ribosomes
increased in the same order as nucleolar
size. Although no clear correlation between
the degree of malignancy of tumor cells
and the behavior of free ribosomes and
RER has been established,36 it is generally
known that rapidly growing cells which require an increased production of protein,
such as embryonic cells and malignant
tumor cells, tend to have a large number of
free ribosomes in the cytoplasm.13 Judging
from the nucleolar structure and the number of free ribosomes, our results seem to
indicate grades of cellular growing activity
increasing from spindle A, through spindle.
B, to epithelioid type, which is consistent
with the expected cellular malignancy of
these classical cell types.1'5 Another interesting correlation can be seen between the
nucleolar size and the number of free ribosomes, which is compatible with the believed function of the nucleolus to produce
ribosomal RNA.37
Generally, RER was the most prominent
in spindle B-type cells, which was predominantly of an elongated form, whereas
in epithelioid type a lesser number of
RER was largely of a short segmented
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form. The number of mitochondria appeared to increase in the order of spindle
A, spindle B, and epithelioid, and the latter
cells tended to show a bizarre form. Concerning the structure of spindle B and
epithelioid cells, our results were similar
to those of Hogan and Feeney9 with respect to the number of free ribosomes
and RER, and confirmative to those of
Kroll and Kuwabara13 in regard to mitochondria.
Cytoplasmic filaments (approximately
60 A in diameter), which have never been
mentioned by earlier observers of uveal
malignant melanomas, decreased in the
order of spindle A, spindle B, and epithelioid. Although the significance of these
filaments is not clear, even more prominent filaments have been seen in the spindle A-type cells of an iris melanoma as
well as in normal iris melanocytes which
we reported elsewhere.27
Other minor differences were as follows:
Indentations of the nuclear surface were
marked in spindles A and B, but appeared
less prominent in the epithelioid type;
longitudinally oriented nuclear indentations in spindle A type may correspond
to the light microscopical line or fold
running along the nuclear long axis.5 In
spindle B, many nuclei showed clumps
of chromatin in both the nuclear periphery
and the central portions, which appeared
to correspond to the coarse chromatin pattern observed in light microscopy of this
type cell.4 Pinocytotic vesicles were the
most prominent in spindle A, whereas thin
cytoplasmic processes were the most remarkable in epithelioid-type cells. Large
Golgi complexes were found in all cell
types; however, these were seen most frequently in epithelioid type cells. While
other organelles appeared similar in all the
cell types, a short cilium could be found
relatively frequently in spindle A-type cells.
In epithelioid type cells, "light" and
"dense" cells were observed by earlier
authors.9'13 In our study, dense cells were
found in both spindle A and epithelioid
types. They were scattered among the
886 hvamoto, Jones, and Howard
•
.
.
*
:
•
:
Investigative Ophthalmitlotiy
November 1972
•
Fig. 8. ("ells of mixed-type melanomas. A. Numerous glycogen particles (arrow) in epithelioid
type cell, r ~~- ribosomes. -38,940. B. An inteniiediate cell, ep = epithelioid-type portion, sp =
spindle B type-portion. -6,900. C. A multinucleated giant melanoma cell, n — nuclei, ep —
epithelioid type-portion, sp
spindle B type-portion. -5.100.
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Volumr 1 1
X II ml HI- 1 1
Ultrastnuttiral comparisons in malignant melanoma 887
Fig. 9. Complementary subjects in uveul malignant melanomas. A. High power of a nonmelani/cd premelanosonie, containing striated h'brillar elements. * 156,600. ft. Premelanosomes
with both fibrillar and granular elements. 44,250. C. Premelanosonies with predominant
granular-elements. *44,250. D to F. Marginal densifications of apposed cell membranes simulating junctional complexes (arrows) in spindle A (D. «70,800), spindle B (E. x 108,000).
and epithelioid type (F. 108,000) melanomas. G. A pore (arrow) of a capillary endotheliuni
in uveal melanoma, bm = basal lamina, \ 1 = vessel lumen. • 162.000. //. A widened intercellular space, containing dense filamentous material ( f ) . collagen fibrils ( c ) , and vesicles ( v ) .
•44,250.
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Investigative Ophthalmology
November 1972
hoamoto, Jones, and Howard
major cells with a lighter cytoplasm, and
appeared to be a simple condensation of
the latter cells. Some of them seemed to
be degenerative, and a sequence from these
degenerated dense cells to a complete
debris could also be found.
In mixed-type melanomas the distinction
of cell types was often difficult because of
the presence of cells regarded as intermediate forms. In our limited cases, however, the major structural features of typical spindle B and epithelioid cells were
similar to those in pure-type melanomas.
Since our studies were confined to the tumor regions with non- or lightly-pigmented
cells, the problem of pigment granules as
well as macrophages remain for future
studies. However, in these regions also
most tumor cells contained pigment granules which were largely immature granules
(premelanosomes)30 composed of both fibrillar and granular elements (Fig. 9 A,
B, and C); only a few mature granules
(melanosomes)30 could be seen in our
study. So far no clear correlation of pigment granules with cellular types could
be found. Regardless of the cell types, some
cells contained premelanosomes with predominantly granular elements (Fig. 9, C),
which in comparison with normal uveal
melanocytes27 appeared abnormal. Similar
premelanosomes predominated in our case
of tapioca melanoma, and this was discussed in relation to a possible "nevoblast"
origin of these cells.-7 While the problems
of extracellular conditions, e.g., attachment
devices,13 connective tissue fibers, and
blood vessels,0 remain for future studies,
the following have been noted in the present study: In areas with compactly arranged melanoma cells (tumor Nos. 1 and
4), the intercellular space was usually
about 200 A apart; in this space, however,
there were sometimes locally widened
zones, which contained dense filamentous
elements, collagen fibrils, and occasional
vacuoles (Fig. 9, H). Local marginal densifications of two apposed cell surfaces,
which simulated junctional complexes,
could be seen in all the cell types (Fig.
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9. D, E, and F); the width of their interspace, however, varied from 100 to 1,000
A (in compact areas, 100 to 200 A). So
far these probable attachment devices were
found most frequently in spindle A-type
melanoma. Blood capillaries in melanoma
tissues often showed pores or fenestrations
of the endothelium (Fig. 9, G).
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