10
LEROY C. S T E V E N S
elements of the tumor. The author observed this type of progression
several times, but erroneously called it a trophoblastic tumor (Stevens,
1958). It contained cells arranged like parietal yolk sac endoderm resting
on Reichert's membrane. The stem cell of the tumor had changed from
a pluripotent cell to one limited in embryonic potency to the production
of endodermal cells. According to Pierce (1961) this would suggest that
embryonal carcinoma cells in a teratoma are a heterogeneous collection,
some multipotential, some determined, but all cancerous. Teilum (1965)
compared this parietal yolk sac carcinoma with homologous growths in
the human ovary and testis.
We are maintaining several transplantable teratomas and have observed stem cell progression. One highly pleomorphic transplantable
teratoma transformed into a myoblastic tumor. It originally contained
neural tissue, cartilage, bone with marrow, various types of eplthelia,
undifferentiated embryonal cells, and muscle. At the fifth transplant
generation all of the original tissues were present, but striated muscle
was a conspicuous component. The sample selected for histological
examination at the twenty-third generation was about half nerve and
half muscle fibers, only a few of which were striated. At the twentyninth generation, all but myoblastic tissue had disappeared. There remained only myoblasts and abnormal muscle fibers. It has remained like
that for 158 transplant generations. There are no undifferentiated embryonal cells; the stem cell has become myogenic.
Some transplantable teratomas are composed solely of neural tissue
(Stevens, 1958). The stem cell, as in the myoblastic and yolk sac tumors,
has become histogenetically determined, and is no longer pluripotent.
Willis (1952) cited a remarkable group of human cases in which small
primary growths of testicular teratomas consisted only of well-differentiated benign-looking tissues, but fatal, rapidly growing métastases
developed. The testis must have originally contained a small but actively
growing tumor which underwent maturation to fully differentiated
quiescent tissues after having metastasized.
Azzopardi et al. (1961) described a series of patients with widespread
malignant teratomas (choriocarcinoma, embryonal carcinoma, and teratocarcinoma). In all 17 cases there were scars in the testis which they
believed to be burned-out primary testicular tumors. Eight of these
contained remnants of mature teratomas. These observations were interpreted to indicate regression of primary tumors after they had
metastasized. Some of these lesions were detected only after careful
search and special study of the testes in patients who had metastatic
tumors of apparent germ cell origin.
A comparable situation where an actively growing tumor becomes
quiescent through differentiation was occasionally observed in strain
LEROY C. S T E V E N S
elements of the tumor. The author observed this type of progression
several times, but erroneously called it a trophoblastic tumor (Stevens,
1958). It contained cells arranged like parietal yolk sac endoderm resting
on Reichert's membrane. The stem cell of the tumor had changed from
a pluripotent cell to one limited in embryonic potency to the production
of endodermal cells. According to Pierce (1961) this would suggest that
embryonal carcinoma cells in a teratoma are a heterogeneous collection,
some multipotential, some determined, but all cancerous. Teilum (1965)
compared this parietal yolk sac carcinoma with homologous growths in
the human ovary and testis.
We are maintaining several transplantable teratomas and have observed stem cell progression. One highly pleomorphic transplantable
teratoma transformed into a myoblastic tumor. It originally contained
neural tissue, cartilage, bone with marrow, various types of eplthelia,
undifferentiated embryonal cells, and muscle. At the fifth transplant
generation all of the original tissues were present, but striated muscle
was a conspicuous component. The sample selected for histological
examination at the twenty-third generation was about half nerve and
half muscle fibers, only a few of which were striated. At the twentyninth generation, all but myoblastic tissue had disappeared. There remained only myoblasts and abnormal muscle fibers. It has remained like
that for 158 transplant generations. There are no undifferentiated embryonal cells; the stem cell has become myogenic.
Some transplantable teratomas are composed solely of neural tissue
(Stevens, 1958). The stem cell, as in the myoblastic and yolk sac tumors,
has become histogenetically determined, and is no longer pluripotent.
Willis (1952) cited a remarkable group of human cases in which small
primary growths of testicular teratomas consisted only of well-differentiated benign-looking tissues, but fatal, rapidly growing métastases
developed. The testis must have originally contained a small but actively
growing tumor which underwent maturation to fully differentiated
quiescent tissues after having metastasized.
Azzopardi et al. (1961) described a series of patients with widespread
malignant teratomas (choriocarcinoma, embryonal carcinoma, and teratocarcinoma). In all 17 cases there were scars in the testis which they
believed to be burned-out primary testicular tumors. Eight of these
contained remnants of mature teratomas. These observations were interpreted to indicate regression of primary tumors after they had
metastasized. Some of these lesions were detected only after careful
search and special study of the testes in patients who had metastatic
tumors of apparent germ cell origin.
A comparable situation where an actively growing tumor becomes
quiescent through differentiation was occasionally observed in strain