Diffuse Embryoma of the Testis - American Journal of Clinical

ANATOMIC PATHOLOGY
Original Article
Diffuse Embryoma of the Testis
An Immunohistochemical Study of Two Cases
MARIZA N. DE PERALTA-VENTURINA, MD, JAE Y. RO, MD, NELSON G. ORDONEZ, MD,
AND ALBERTO G. AYALA, MD
staining for a-fetoprotein and strong staining for cytokeratin, whereas
the EC component was positive for Ki-1 (BerII2, CD30) antigen, was
negative for a-fetoprotein, and stained more weakly for cytokeratin.
The randomly distributed few trophoblastic elements stained for human chorionic gonadotropin. The patients are alive with no evidence of
disease, 11 years and 9 months after surgery, respectively. This newly
described but distinct variant of mixed-germ-cell tumor should be differentiated from polyembryoma, which is composed of multiple discrete embryoid bodies. (Key words: Diffuse embryoma; Immunohistochemistry; Mixed-germ-cell tumor; Testis) Am J Clin Pathol
1994;101:402-405.
In 1983, Cardoso de Almeida and Scully1 first described a distinctive form of mixed-germ-cell tumor (MGCT) characterized by a diffuse, orderly arrangement of embryonal carcinoma
(EC) and yolk sac tumor (YST) with scattered trophoblastic
elements; they called this tumor "diffuse embryoma of the testis." To our knowledge, no additional cases have been reported. We describe two cases of diffuse embryoma of the testis
for which we performed histologic and immunohistochemical
studies. Immunohistochemical evaluation can help to distinguish diffuse embryomas from polyembryomas and other
forms of malignant MGCTs.
mary antibodies used were a cocktail of three anticytokeratin
mouse monoclonal antibodies (1:50 CAM 5.2, Becton Dickinson, Mountainview, CA, and 1:400 AE1 and AE3, BoehringerMannheim, Indianapolis, IN), a-fetoprotein (AFP) (1:200;
Biogenex, San Ramon, CA), human chorionic gonadotropin
(HCG) (1:1000; Dako, Carpinteria, CA), and Ki-1 (1:20
BerH2, CD30, Dako). The immunoreaction was visualized
with 3-amino-9-ethylcarbazole as a chromogenic substrate.
The specificity of the immunoreaction was verified by staining
known positive and negative control tissue sections.
RESULTS
MATERIALS A N D METHODS
Case 1
Records of both cases were retrieved from The University of
Texas M. D. Anderson Cancer Center (Houston, TX) consultation files. Three hematoxylin-and-eosin-stained slides were
available for study from one patient and eight from the other.
Clinical information, including postoperative data, was obtained from the patients' medical records and primary physicians.
Immunohistochemical studies were performed on formalinfixed, paraffin-embedded tissue sections by the avidin-biotinperoxidase complex method of Hsu and colleagues.2 The pri-
The patient was a 37-year-old man with a 6-month history of
right testicular swelling. His preoperative HCG and AFP levels
were 117 mlU/mL and 400 ng/mL, respectively. He underwent right radical orchiectomy in an outside hospital. Postoperatively, he was referred to the M. D. Anderson Cancer Center
for further evaluation. Results from the subsequent work-up,
including a computerized tomographic scan of the abdomen
and pelvis, chest x-ray, and evaluation of serial HCG and AFP
levels in serum, were normal. The patient was determined to
have had stage I disease. He has been disease-free for 11 years.
Case 2
From the Department of Pathology, The University of Texas M. D.
Anderson Cancer Center, Houston, Texas.
Manuscript received December 9, 1993; revision accepted March 2,
1994.
Address reprint requests to Dr. Ro: Department of Pathology, Box
85, The University of Texas M. D. Anderson Cancer Center, 1515
Holcombe Boulevard, Houston, TX 77030.
402
The patient was a 38-year-old man who had a 2-week history
of a swollen, nonpainful right scrotum after mild trauma. On
examination, the testis was hard, firm, and enlarged but without nodularity. Ultrasound examination showed enlargement
of the right testicle but no obvious hyperechoic or necrotic
tissue to suggest malignancy. The patient's left testicle was normal. Initial HCG and AFP levels were 37 mlU/mL and 2000
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The authors report the histologic and immunohistochemical findings of
two cases of diffuse embryoma of the testis, a distinct form of mixedgerm-cell tumor characterized by diffuse, orderly arrangement of embryonal carcinoma (EC) and yolk sac tumor (YST) with scattered trophoblastic components. The patients were 37 and 38 years old when
they presented with a right testicular tumor, which was confined to the
testis (stage I) in both cases. Histologically, the tumor was composed
predominantly of intimately intermingled EC and YST components in
almost equal proportion. The tumor cells were arranged in necklacelike
fashion; the EC cells formed glandular structures rimmed by a single
cell layer of YST cells. The YST component was highlighted by positive
DE PERALTA-VENTURINA ET AL.
Diffuse Embryoma of the Testis
403
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FIG. 1. (Top left) Yolk sac tumor (YST) component (curved arrow) enwraps embryonal carcinoma (EC) component (straight arrow). The YST
shows a reticular pattern, and the EC has a papillary growth pattern (hematoxylin and eosin, X40).
FIG. 2. (Top right) Glandular structures lined by tall columnar pleomorphic cells typical of EC are encircled by a row of flattened YST cells in
necklacelike fashion (hematoxylin and eosin, XI00).
FIG. 3. (Bottom left) Diffuse intermingling of EC and YST components (hematoxylin and eosin, X100).
FIG. 4. (Bottom right) Glandular structure with EC and YST. There is strong cytokeratin immunoreactivity in the YST component and weak
reactivity in the EC component (avidin-biotin-peroxidase complex immunostain, X200).
Vol. 102. No. 4
404
ANATOMIC PATHOLOGY
Original Article
TABLE 1. CLINICOPATHOLOGIC FEATURES OF DIFFUSE EMBRYOMA OF THE TESTIS
Initial Serum
Markers
Case
Age
(yrs)
HCG
(mlUlmL)
AFP
(nglmL)
Treatment
Gross Findings
Components
Stage
Follow-up
> 1,300
2,880
Orchitectomy,
+RLND,
chemotherapy,
radiotherapy
8 cm yellow and tan
with center, firm
nodular, redyellow
NA
NA
DOD (metastasis to
liver, LN, bone,
17 months)
2'
29
1,400
1,600
Orchitectomy,
-RLND,
chemotherapy
8 cm, soft, gray with
necrosis and
hemorrhage
NA
NA
NED, 18 months
3 Present Case
(Case 1)
37
117
400
Orchiectomy only
size not specified,
with areas of
necrosis and
hemorrhage
EC < 50%
YST < 50%
Chorio 1%
I
NED, 11 years
4 Present Case
(Case 2)
38
37
2,000
Orchiectomy only
5 cm, focal
hemorrhage and
necrosis
EC 50%
YST 50%
I
NED, 9 months
* HCG = human chorionic gonadotropin: AFP = alpha-fetoprotein; RLND = retroperitoneal lymph node dissection (+, positive for
tumor: -, negative for tumor); NA = not available; EC = embryonal carcinoma; YST = yolk sac tumor; Chorio = choriocarcinoma; DOD =
dead of disease; NED = no evidence of disease.
ng/mL, respectively. The patient subsequently underwent right
inguinal orchiectomy in an outside hospital. The results of postoperative computerized tomographic scan of the abdomen and
pelvis and x-ray of the chest were negative for disease. The
patient's most recently measured HCG and AFP levels (9
months after surgery) were within normal limits. It was concluded that he had had stage I disease. The patient has been
disease-free for 9 months.
In both cases, the tumors were confined to the testis without
extension into the tunica albuginea, epididymis, or spermatic
cord. The clinical and gross pathologic features of the two cases
and of the two previously reported cases1 are presented in
Table 1.
Histologic
Features
Specimens from both cases showed a diffuse, orderly arrangement of EC and YST components (Fig. 1). This intimate intermingling of EC and YST cells was present in 99% of the tumor
in case 1 and 100% of the tumor in case 2. A small component
of choriocarcinoma made up 1% of the tumor in case 1. Scattered syncytiotrophoblastic cells were found in both cases. In
case 2, the finely reticulated pattern of YST appeared to encircle the glandular structures formed by EC in necklacelike fashion (Fig. 2). In case 1 the arrangement was less orderly; however, EC and YST cells were diffusely intimately intermingled
(Fig. 3), and no areas had only one of these components, even
at low-power magnification. The cells in the center of the glandular structures had the large hyperchromatic nuclei typical of
EC, with prominent nucleoli, whereas the cells at the periphery
have the typical reticulated pattern of YST.
Immunohistochemical
Findings
The unique spatial relation of the EC and YST cells was
highlighted by the distinctive immunoreactivity of the two com-
ponents for cytokeratin, AFP, and Ki-1. Although both EC and
YST cells are immunoreactive for cytokeratin, the cells identified on routine staining as EC cells stained less strongly than
did YST cells (Fig. 4). Only the YST cells were positive for AFP
(Fig. 5A). The Ki-1 antigen, initially used as a hematopoietic
tissue marker, produced a positive reaction in cells identified
on routine staining as EC cells (Fig. 5B). The randomly distributed, isolated trophoblastic elements stained strongly for HCG.
DISCUSSION
Mixed-germ-cell tumors of the testis are a heterogeneous
group of neoplasms composed of germ-cell elements in varying
combinations and proportions. Most often, these tumors are
characterized by a haphazard intermingling of EC, YST, and
teratomatous and choriocarcinomatous elements. However, in
four cases, a diffuse, orderly arrangement of EC and YST with
scattered trophoblastic elements, singly or in small groups
within the septa and also in juxtaposition to EC cells, has now
been observed. This rare entity, called diffuse embryoma of the
testis, should be differentiated from polyembryoma of the testis. The latter is a germ-cell neoplasm composed entirely of
blastocytelike embryoid bodies showing features of presomite
embryos that have not developed beyond the 18- to 20-day
stage.3 These discrete embryoid bodies, which are composed of
an embryonic disk and amniotic and yolk sac cavities, may also
be present focally in otherwise ordinary MGCTs. There is no
agreement concerning the origin of the embryoid bodies; most
researchers believe that the bodies probably arise from the multipotential malignant embryonal cells within the tumor. 3
Because of the intimate intermingling of the EC and YST
cells, a concomitant YST component in what appears to be a
pure EC may be overlooked, or vice versa. An increased serum
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DE PERALTA-VENTURINA ET AL.
405
a of the Testis
REFERENCES
FIG. 5. Only the YST cells are stained for a-fetoprotein (avidin-biotinperoxidase complex immunostain, X100) (A), whereas the EC cells are
positive for Ki-1 (ABC immunostaining, X200) (B).
AFP level in a patient with an apparently pure EC may indicate
diffuse embryoma.
Although Cardoso de Almeida and Scully1 originally described EC, YST, and trophoblastic elements as being diffusely
and orderly arranged, according to their microscopic description and illustrations the trophoblastic elements were more
randomly scattered. The histologic features of our cases were
similar to those described by Cardoso de Almeida and Scully.1
a-Fetoprotein immunostaining is found almost exclusively
in YST. Although most ECs are negative for AFP, on occasion
a few may express this marker, but the reactivity is usually
confined to scattered cells.4 On the other hand, staining for
1. Cardoso de Almeida P, Scully R. Diffuse embryoma of the testis: A
distinctive form of mixed germ cell tumor. Am J Surg Pathol
1983;7:633-642.
2. Hsu S, Raine L, Fanger H. Use of avidin-biotin-peroxidase complex (ABC) in immunoperoxidase techniques: A comparison
between ABC and the unlabeled antibody (PAP) procedure. J
Histochem Cytochem. 1981;29:577-580.
3. King M, Hubbell, M, Talerman A. Mixed germ cell tumor of the
ovary with a prominent polyembryoma component. Int J Gynecol Pathol 1991;10:88-95.
4. Mostofi F, Sesterhenn I, Davis C. Immunopathology of germ cell
tumors of the testis. Semin Diagn Pathol 1987;4:320-341.
5. Ro JY, Sahin AA, Ayala AG, et al. Lung carcinoma with metastasis to testicular seminoma. Cancer 1990;66:347-353.
6. Pallesen G, Hamilton-Dutoit S. Ki-1 (CD 30) antigen is regularly
expressed by tumor cells of embryonal carcinoma. Am J Pathol
1988;133:446-450.
7. Takeda A, Ishizuka T, Goto T, et al. Polyembryoma of ovary producing alpha-fetoprotein and HCG: Immunoperoxidase and
electron microscopic study. Cancer 1982;49:1878-1889.
8. Ro JY, Dexeus F, El-Naggar A, Ayala AG. Testicular germ cell
tumor: Clinically relevant pathologic finding. Pathol Annu
1991;26:59-87.
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Ki-1 antigen, once thought to be an exclusive hematopoietic
cell marker, can be seen in EC but not in any other testicular
tumor. 5,6 In both of our cases, the YST cells reacted more
strongly with the anticytokeratin cocktail than did the EC cells,
a helpful distinction to delineate the presence of two germ-cell
elements. These findings were in agreement with the immunohistochemical results of Cardoso de Almeida and Scully,1 except that Ki-1 staining was not performed in their two cases.
Our cases have shown the invaluable role of immunohistochemistry in delineating specific components in an MGCT. However, in most instances, histologic evaluation alone may be all
that is necessary.
Immunohistochemical studies have also been performed on
embryoid bodies. Takeda and coworkers7 found AFP expression in areas that correspond to the yolk sac of the embryoid
bodies, which is composed of a small cluster of cells around the
yolk sac cavity of each embryoid body. This finding is in contrast to the interstitial and more diffuse staining in YST cells
for AFP in cases of diffuse embryoma.
This rare, distinct histologic subtype of MGCT should be
recognized, although the biologic behavior of MGCT depends
primarily on the stage of the disease.8 A diagnosis of this tumor
implies an equal percentage of YST and EC components,
which are intimately mixed within the tumor. The term "diffuse embryoma" seems to be accurate because of the diffuse
nature of the lesion and the formation of pseudoembryoid bodies, in contrast to the focal nature and presence of classic
embryoid bodies in polyembryoma.
The presence of EC and YST components within the same
MGCT is not infrequent. However, diffuse embryoma characterized by orderly arrangement of EC and YST in approximately equal proportions is, in our experience, truly rare.