Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Toshiki Yamasaki is active.

Publication


Featured researches published by Toshiki Yamasaki.


Radiotherapy and Oncology | 1990

Supratentorial malignant glioma: an analysis of radiation therapy in 178 cases

Yuta Shibamoto; Junkoh Yamashita; Masaji Takahashi; Toshiki Yamasaki; Haruhiko Kikuchi; Mitsuyuki Abe

To analyze treatment results of supratentorial malignant gliomas in the megavoltage era, all the histologic specimens were reviewed and glioblastoma multiforme (GBM) was distinguished from anaplastic astrocytoma (AA) by the presence of necrosis. Among those who had completed radiotherapy and who had been followed for at least one year, 135 GBM and 43 AA patients were found. The median survival time (MST) after operation was 12 months for GBM and 18 months for AA. The 5-year survival rate was 0.9% for GBM and 18% for AA. The size of radiation field had little influence on survival time; MST was 12 months for GBM patients treated with a local field covering tumor plus less than 2 cm margin, 12 months for those treated with a generous field (2 cm or more margin), and 13 months for those treated to whole brain. Also for AA, whole brain radiation did not prolong survival. Initial relapse of GBM and AA developed within the irradiated volume in 86% of the cases treated with a generous field. Whole brain radiation seemed useless for the treatment of malignant gliomas. Survival time appeared to be dose-dependent; MST was 10, 13, and 16 months for GBM patients who received 45-57, 57-63, and 63-72 Gy, respectively. Extensive surgical resection was associated with a better prognosis in GBM. AA patients 60 years old or older had a poorer prognosis than younger patients, but age was not a significant prognostic factor for GBM. Chemotherapy appeared to prolong survival slightly without improving long-term survival.(ABSTRACT TRUNCATED AT 250 WORDS)


Neurosurgery | 1989

Primary spinal intramedullary malignant melanoma: case report

Toshiki Yamasaki; H. Kikuchi; Junkoh Yamashita; Reinin Asato; Mayumi Fujita

A rare case of primary spinal intramedullary malignant melanoma at the T6 level in a 31-year-old man is presented. The tumor was partially removed, and neuroaxis irradiation up to 50 Gy was then administered. Subsequently, systemic interferon beta (specific activity, 2.0 X 10(8) IU/mg protein) therapy (total dose, 2.2 X 10(7) units) was begun. At the completion of these therapies, immunohistochemical analysis with monoclonal antibodies against melanoma-associated antigens confirmed the presence of melanoma cells in the cerebrospinal fluid (CSF). Chemotherapy with intrathecal administration of dacarbazine (dimethyltriazenoimidazole carboxamide, DTIC) was then initiated, to avoid the dissemination of tumor cells by the CSF. Periodic cytological examination of CSF for melanoma cells revealed a marked reduction in the number of tumor cells. Pharmacokinetic study showed that the disappearance of DTIC from the CSF was biphasic, with an initial half-life of 30 minutes and a terminal half-life of 5 hours. Follow-up examination by MRI 1 year after the operation did not disclose any significant increase in size of the residual tumor. Neither recurrence nor metastasis was observed. The pertinent literature on spinal cord melanoma is reviewed, and the usefulness of MRI and intrathecal chemotherapy with DTIC is discussed.


Surgical Neurology | 1990

Two surgically cured cases of subependymoma with emphasis on magnetic resonance imaging

Toshiki Yamasaki; H. Kikuchi; Toshio Higashi; Hirohiko Yamabe; Kouzo Moritake

The authors describe two surgically cured cases of symptomatic subependymomas located in the lateral ventricle and septum pellucidum with emphasis on magnetic resonance imaging study. Both computed tomography and MRI revealed a calcified mass with repeated intratumoral hemorrhages. Cerebral angiograms disclosed rather hypovascular lesions. The histologic diagnosis was proven to be of subependymoma. The pertinent literature of surgically treated subependymomas is reviewed, and the characteristic biologic features are also discussed.


Surgical Neurology | 1984

Intracranial cavernous angioma angiographically mimicking venous angioma in an infant

Toshiki Yamasaki; Hajime Handa; Junkoh Yamashita; Kouzo Moritake; Shiro Nagasawa

We present a case of a 15-month-old infant with intracranial cavernous angioma in the right frontal lobe in which the cerebral angiogram revealed transmedullary collecting veins characteristic of venous angioma around the lesion. This vascular malformation was histologically confirmed to be a cavernous angioma.


Journal of Neuro-oncology | 1986

Induction of human glioma-specific cytotoxic T-lymphocyte lines by autologous tumor stimulation and interleukin 2

Shin-ichi Miyatake; Hajime Handa; Junkoh Yamashita; Toshiki Yamasaki; Masamichi Ueda; Yuziro Namba; Masao Hanaoka

SummaryTwo human glioma-specific cytotoxic T-lymphocyte (G-S-CTL) lines were established by autologous tumor stimulation (ATS) with the aid of lectin free interleukin 2 (IL 2). Coculture of patients peripheral blood lymphocytes and autologous irradiated glioma cells and subsequent addition of partially purified IL 2 enhanced the tumoricidal activity of the lymphocytes. These CTL lines possessed cross-cytotoxic activity against autologous and allogeneic glioma cells and exhibited low cytotoxic activity against non-glial tumor cells. They did not lyse autologous lymphoblasts. This phenomenon suggested the existence of a common gliomaspecific antigen recognized by the CTL lines.T-cell subset depletion test revealed that the major surface phenotype of G-S-CTL line, responsible for cytotoxic activity was OKT 3 positive, OKT 4 negative and OKT 8 positive.G-S-CTL lines were composed of a low proportion of OKT 8 positive subpopulation after primary ATS and successive propagation with IL 2. The proportion of OKT 8 positive subpopulation was increased by secondary ATS, which enhanced the cytotoxic activity to glioma cells more effectively.


Surgical Neurology | 1986

Suprasellar germinoma with shunt metastasis report of a case with an immunohistochemical characterization of the lymphocyte subpopulations

Jonathan T. Paine; Hajime Handa; Toshiki Yamasaki; Junkoh Yamashita

A case of suprasellar germinoma metastatic to the peritoneum 3 years after the placement of a ventriculoperitoneal shunt is presented. The excised metastatic germinoma was analyzed immunohistochemically with monoclonal antibodies against human lymphocyte subpopulations. Approximately 80% of the lymphocytes expressed pan-T, or Leu-1, surface antigens, and 20% were B1+, or B cells. Approximately 30% of T cells were Leu-2+, or cytotoxic and suppressor cells; 70% were Leu-3+, or helper cells. The large number of T cells is consistent with their role in cell-mediated immunity; their subpopulation ratio approximated that of the circulation. The literature pertinent to germinoma shunt metastasis is also reviewed.


Surgical Neurology | 1985

Cavernous angioma in the fourth ventricle

Toshiki Yamasaki; Hajime Handa; Kouzo Moritake

A cavernous angioma in the fourth ventricle of a 47-year-old man is reported. Because of a progressive clinical course and a ring-like enhancement on computed tomography, a brain tumor, rather than a vascular disease, was suspected. The lesion was removed totally and verified histologically as a cavernous angioma.


Surgical Neurology | 1992

Glial cyst of the pineal gland with characteristic computed tomography, magnetic resonance imaging, and pathological findings: Report of two cases

Shin-ichi Miyatake; Haruhiko Kikuchi; Toshiki Yamasaki; Toyoaki Terashima; Minoru Asahi; Reinin Asato; Kayoko Higuchi; Yasuaki Nakashima

Two cases of glial cyst of the pineal gland are documented. Preoperative computed tomography and magnetic resonance imaging revealed cystic lesions of the pineal region with contrast enhancement of the walls, suggesting neoplastic lesions rather than true cysts. However, the histopathological examination of the resected specimens revealed the presence of glial tissue and normal structure of pineal gland and capsule, characteristics that were consistent with those of glial cysts of the pineal gland. Headache and visual disturbance were resolved after total removal of the cysts.


Cellular Immunology | 1990

Clonal analysis in the ultrastructure of cell-to-cell interaction between a human glioma cell line and autologous tumor-specific cytotoxic T lymphocytes

Kouichi Iwasaki; Haruhiko Kikuchi; Shin-ichi Miyatake; Yoshifumi Oda; Junkoh Yamashita; Toshiki Yamasaki

The clonal analysis in the ultrastructure of tumor-lymphocyte interaction was carried out in order to investigate the precise mechanism responsible for CTL-mediated cytolysis of tumor cells. A glioma-derived cell line (GI-1) and autologous tumor-specific cytotoxic T lymphocyte (CTL) clones were established. The CTL lines were composed of the morphologically homogeneous lymphocytes with intracytoplasmic electron-dense secretory granules. After the stimulation by GI-1, the size of the CTLs increased, and the intracytoplasmic organellas were developed. It was noted that the intracytoplasmic secretory granules markedly increased in number and size, and many of them exhibited an immature appearance. On the other hand, the tumor cells underwent a progressive degeneration. In contrast, the stimulation by other antigens caused only small morphological changes in the CTLs. It is suggested, therefore, that the secretory function of tumor-specific CTLs is activated by the stimulation of the specific antigen, and that soluble factors in the secretory granules in the CTLs may be closely associated with the mechanism of target cell lysis.


Surgical Neurology | 1990

Intracerebral malignant lymphoma with fluctuating regression and spatial evolution

Toshiki Yamasaki; H. Kikuchi; Junkoh Yamashita; Kouzo Moritake; Yuuta Shibamoto; Jonathan T. Paine; Nobuko Shima; Hirohiko Yamabe

Seven patients with histologically proven primary intracerebral malignant lymphoma, characterized by a fluctuating nature with both transient regression and spatial evolution of the tumors without contiguity to the initial lesion, are presented. Although the overall outcome was unfavorable, two cases had a long-term survival of 3 years or more and one of them showed a good quality of life. Correlation among characteristic clinical presentations, computed tomography scans, and prognostic factors after management with surgery, radiation, and chemotherapy, including steroids, is discussed.

Collaboration


Dive into the Toshiki Yamasaki's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge