cxEPA
United States *•
Environmental Protection
Agency
Office of
Pesticide Programs
54019873
Classification of
Prdriferatiye Hepati c
Lesions in Mice
"j -H ''"•
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CLASSIFICATION OF PROLIFERATIVE HEPATIC
LESIONS IN MICE - AN EPA SPONSORED WORKSHOP1
The Steerinq Committee
Dr. Joseph Burek, Dr. Charles Frith, Dr. F. M. Garner,
Dr. Bernard Haberman, Mr. Steve Johnson, Dr. Sidney Jones,
Dr. Ronald L. Schueler, Dr. Robert A. Squire, Dr. James Stookey,
Ms. Vivian Turner, Dr. Jerrold M. Ward, Dr. Adrienne Zahner
iThis report has been reviewed by the Office of Pesticides and
Toxic Substances, U.S. Environmental Protection Aaency, and
approved for publication. Approval does not siqnify that the
contents necessarily reflect the views and policies of the U.S
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
of use.
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ABSTRACT
The Environmental Protection Aqency (EPA) sponsored a
workshop in 1980 to characterize and classify hepatic neoplasms
in mice. The principal qoal of the workshop was to develop a
guideline in the diagnosis and interpretation of hepatic lesions
in the mouse commonly observed in oncoqenicity tests. Criteria
for classification were reached by a consensus of the workshop
participants.2 This nomenclature was proposed to brinq
consistency in the diagnosis and interpretation of mouse liver
neoplasms. Participants agreed that future research findings
might alter this terminology as new information on the biological
behavior of these neoplasms emerges.
Lesions were classified as follows: (1) Focus of cellular
alteration (2) hepatocellular adenoma (3) hepatocellular
carcinoma and (4) non-hepatocytic malignant neoplasms of
cholangiolar or vascular origin.
Criteria for characterization of lesions were given.
^Dr Gary Boorman, Dr. Joseph Burek, Dr. Alex Cameron, Dr. Charles
Frith, Dr. F.M. Garner, Dr. Dawn G. Goodman, Dr. Paul Grasso, Dr.
Richard A. Griesemer, Dr. Bhola Gupta, Dr. Bernard Haberman, Dr.
Jerry Hardisty, Dr. G.H. Hottendorf, Mr. Stephen Johnson, Dr.
Sidney Jones, Dr. Shoichi Katayama, Dr. Choudari Kommineni, Dr.
Michael Lipsky, Dr1. Ernest E. McConnell, Dr. Ronald Moch, Dr.
Richard J. Montali, Dr. James A. Popp, Dr. Melvin Reuber, Dr.
Boris Reubner, Dr. Gerd Reznik, Dr. Ronald L. Schueler, Dr.
Stewart Sell, Dr. Winslow Sheldon, Dr. Robert A. Squire, Dr.
Sherman Stinson, Dr. James Stookey, Dr. Glen Todd, Dr. John Toft,
Dr. Leander Tryphonas, Dr. Jerrold M. Ward, Dr. Morris A.
Weinberger, Dr. Adrienne Zahner, Dr. Chris Zurcher.
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INTRODUCTION
The qoal of the workshop was to develop a guideline for use
by patholoqists. Such a guideline would provide a meaninqful and
loqical standard to judqe the siqnificance of liver lesions in
mice from oncoqenicity and toxicity testinq. Scientists with
extensive experience in patholoqy and in diaqnosis and
interpretation of proliferative lesions of the mouse liver
participated to develop the quidance.
Studies have shown wide differences of opinion reqardinq the
classification and nature of lesions of the mouse liver. A
variety of terms have been employed to describe beniqn and
maliqnant neoplasms commonly encountered in laboratory mice.
It is well established that the mouse liver is often a
tarqet orqan in toxicity and oncoqenicity testinq. Since the
results of these tests may serve as the scientific basis for
requlatory decisions, a standardized classification and
nomenclature for identification of lesions in the mouse liver is
essential.
3
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MATERIALS AND EVALUATIONS
Mouse liver sections for microscopic evaluation were
selected from the National Center for Toxicoloqical Research and
the National Cancer Institute/National Toxicology Proqram to
provide a full spectrum of hepatocellular lesions commonly
observed in bioassay testinq. Duplicate slide sets were prepared
from Bouin1s-fixed tissues, stained with hematoxylin and eosin,
and distributed to participants in advance of the workshop.
Animal histories, includinq a qross description of liver lesions
at necropsy, were submitted with the microslides. Diaqnoses and
opinions concerninq the nature of the lesions were submitted
prior to the workshop; the results were tabulated and distributed
at the workshop.
Photomicroqraphs were made of representive microscopic
lesions for presentation. At the workshop projected
photomicrographs were evaluated.
At the end of two and one-half days of presentation,
discussion, review and votinq, a consensus was reached reqardinq
diaqnosis and interpretation of the proliferative hepatocellular
chanqes that are commonly observed in the mouse liver.
Participants defined and established criteria for common
occurrinq lesions, to establish an uniform nomenclature.
CRITERIA AND DISCUSSION
The followinq criteria for classification of proliferative
hepatocellular lesions frequently seen in the mouse liver were
arrived at by consensus. Photomicroqraphs were selected to
demonstrate features or criteria aqreed to by participants and
represent only a portion of the slides actually reviewed by
participants.
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FOCUS OF CELLULAR ALTERATION; Foci are generally less than
a lobule in size, but may occasionally occupy a few lobules.
Cytoplasm may be basophilic (Fiq. I), vacuolated (Fict. 2),
eosinophilic (Fig.3), or a combination of these cell types.
Compression may not be a feature of this lesion. The term
preneoplasia should be avoided in connection with foci because
their tru^ nature is not well defined.
HEPATOCELLULAR ADENOMA; Adenomas are generally several
lobules in size or greater. Compression is prominent or
significant. The lobular pattern of architecture is lost and
cells are arranged as single or multiple-cell thick trabeculae
which may be disoriented and lack continuity with adjacent normal
tissue. Hepatocytes are generally uniform in size and shape,
well-differentiated, and may be basophilic (Fig. 4), vacuolated
(Fig. 5), eosinophilic or combinations of these cell types (Fig.
6). Some pleomorphism may occur (Fig, 7). The degree of
trabeculae formation and pleomorphism differentiates adenoma from
carcinoma.
Adenomas should not have portal triads associated with a
normal lobular pattern, but triads may be entrapped in the
lesion.
HEPATOCELLULAR CARCINOMA; General features are similar to
adenoma, except that the trabeculae formation is often more
prominent and several cells thick, and formation of acinar
structures are sometimes observed (Fig. a). The degree of
cellular pleomorphism or atypia is more pronounced than in
adenoma (Fig. 9). Transitional varieties consisting of a
combination of hepatocytes and cells suggestive of biliary origin
are less frequently observed, (Fig. 10, 11).
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NON-HEPATOCYTIC (CHOLANGIOLAR AND VASCULAR) MALIGNANT
NEOPLASMS: These occur in the mouse liver; however, the
incidence is much less than that for neoplasms of hepatocytic
oriqin.
C HOLA NGIPC ARCINOMA: This lesion always occurs in
conjunction with hepatocellular tumor. Prominant qlandular
patterns (Fiq. 12) and proliferatinq, hyperchromatic,
undifferentiated biliary epithelium forminq qlandular structures
(Fiq. 13) are observed.
HRMANGIOSARCOMA; The pale neoplasm showinq irreqular blood-
filled spaces and numerous thrombi (Fiq. 14) and a hiqher
maqnification (Fiq. 15) demonstrates that larqe and small blood
spaces are filled with spindle-shaped endothelial cells.
CONCLUSIONS
The concept of focal hyperplasia of hepatocytes exists
between the cateqories of foci of altered cells and adenoma, and
an attempt was made to define this chanqe. None of the
participants, however, were able to provide convincinq examples
of this lesion in the mouse liver.
The terminoloqy and criteria suqqested for use in evaluation
of proliferative hepatocellular lesions in the mouse represent
the current level of research and combined experiences -of the
participants of the workshop. The system of classification can
serve as a framework to have consistency in diaqnosis and
interpretation of mouse liver neoplasms.
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Ac k n ow1e dgme n t
Photomicrographs were provided through the courtesy of Dr.
Sidney Jones, then Director of the Division of Veterinary
Pathology Armed Forces Institute of Pathology, Washington, D.C.
For the review of this manuscript, we express appreciation
to: Drs. Mary Argus, Diane Beal, Richard Hill, Stephanie Irene
and Daljit Sawhney of EPA, and Drs. Robert Maronport (MIEHS) and
Jerrold Ward (NCI).
Particular credits are given to Dr. Diane Beal for the
support in finalizing this report.
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Leqend
Fiq 1. Focus of cellular alteration. The focus is
basopilic, less than one lobule in size and may not compress
surroundinq tissues. H & E, x 160.
Fiq 2. Focus of cellular alteration. The focus shows
hepatocytes with vacuolated or rarefied cytoplasm. H & E, x 25.
Fiq. 3. Focus of cellular alteration. An eosinophilic
focus sliqhtly larqer than one lobule. Cells are larqer than
normal adjacent cells. H & E, x 65.
Fiq. 4. Hepatocellular adenoma. Compression of adjacent
parenchyma is present (at lower left and top-center of
photomicroqraph), and lobular architecture is obliterated.
Basophilic hepatocytes are arranqed in a trabecular pattern. H &
E, x 65.
Fiq. 5. Hepatocellular adenoma. Compression is distinct;
lobular architecture is disrupted; and hepatocytes are pale and
vacuolated. H & E, x 10.
Fiq. 6. Hepatocellular adenoma consistinq of a combination
of eosinophilic and basophilic hepatocytes. H & E, x 10.
Fiq 7. Increased maqnification of hepatocellular adenoma
shown in Fiq. 6. Hepatocytes are eosinophilic or basophilic and
show a mild deqree of pleomorphism. H & E, x 160.
Fiq. 8. Hepatocellular carcinoma. The carcinoma is well
differentiated and has a prominent trabecular pattern that is two
or more cells thick. A zone of compression can be seen at the
junction of the neoplasm and the normal hepatic parenchyma. H &
E, x 160.
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Fiq. 9. Hepatocellular carcinoma. The carcinoma is
poorly differentiated and its prominent trabeculae are several
cells thick. H & E, x 160.
Fiq. 10. Hepatocellular carcinoma. A focus of transition
between iiepatocytes and irreqular qlandular structures resemblinq
biliary epithelium is illustrated. H & E, x 160.
Fiq. 11. Hepatocellular carcinoma. Focal change within a
carcinoma sugqestinq transition from dark, polyhedral hepatocytes
to pale, irregularly fusiform biliary epithelium. H & E, x 160.
Fiq. 12. Cholanqiocarcinoma. Prominent qlandular qrowth
pattern is noted at low maqnification. H & E, x!5.
Fiq. 13. Hiqher maqnification of cholanqiocarcinoraa from
Fiq. 12. Proliferatinq, hyperchromatic, and undifferentiated
biliary epithelium forminq qlandular structures. H & E, x 160.
Fiq. 14. Hemanqiosarcoma. The pale neoplasm contains
irreqular blood-filled spaces and numerous thrombi. H & E, x 15.
Fiq. 15. Hiqher maqnification of hemanqiocarcoma in Fiq.
14, demonstratinq larqe and small blood-filled spaces formed by
plump, spindle-shaped endothelial cells. Hepatocytes appear
trapped within the lesion. H & E, x 160.
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Fiq. 1: Focus of cellular alteration. The focus is
basophilic, less than one lobule in size and does not
compress. X160.
10
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Fig. 2: Focus of cellular alteration. The focus shows
hepatocytes with vacuolated or rarefied cytoplasm. X25.
11
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3: Focus of cellular alteration. As eosinophilic
focus sliqhtly larqer than one lobule. Cells are larqer
than normal adjacent cells. X65.
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Fiq. 4: Hepatocellular adenoma. Compression of adjacent
parenchyma is present ( to lower left and top-center of
photomicrograph) and lobular architecture is obliterated.
Basophilic hepatocytes are arranqed in a trabecular pattern,
X65.
13
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Fig. 5: Hepatocellular adenoma. Compression is distinct
lobular architecture is disrupted and hepatocytes are pale
and vacuolated. X10.
14
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Fiq. 6: Hepatocelluar adenoma consistinq of a combination
of eosinophilic and basophilic hepatocytes. XlO.
15
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Fiq. 7: Increase maqniEication of hepatocellular adenoma
shown in Fiq 6. Hepatocytes are eosinophilic or basophilic
and show a mild deqree of pleomorphism. X160.
16
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Fig. 8: Hepatocellular carcinoma. The carcinoma is well
differentiated, has a prominent trabecular pattern that is
2 or more cells thick. A zone of compression can he seen at
the junction of the neoplasm and the normal hepatic
parenchyma. X160
17
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Fig. 9: Hepatocellular carcinoma. The carcinoma is poorly
differentiated and its prominent trabeculae are several
cells thick. X160.
18
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Fig. 10: Hepatocellular carcinoma. A focus of transition
between hepatocytes and irreqular glandular structures
resembling biliary epithelium. X160.
19
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Fiq. 11: Hepatocellular carcinoma. Focal chanqe within a
carcinoma suqqestinq tranisiton from dark, polyhedral
hepatocytes to pale, irreqularly fusiform biliary
epithelium. X160.
20
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Fiq. 12: Cholanqiocarcinoma. Prominent qlandular qrowth
pattern is noted at low maqnification. X15.
21
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Fiq. 13: Hiqher maqnification of Fiq. 12. Proliferatinq,
hyperchromatic, undifferentiated biliary epithelium
forminq qlandular structures. X160.
22
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Fig. 14: Hemangiosarcoma. The pale neoplasm contains
irregular blood-filled spaces and numerous thrombi. X15
23
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Fiq. 15: Hemanqiosarcoma. Hiqher maqnification of Fiq. 14,
demonstratinq larqe and small blood-filled spaces, formed by
plump, spindle-shaped endothelial cells. Hepatocytes cells.
Hepatocytes appear trapped within the lesion. X160
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