Masai, Kyohei

写真a

Affiliation

School of Medicine, Department of Surgery (General Thoracic Surgery) (Shinanomachi)

Position

Assistant Professor/Senior Assistant Professor
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Career 【 Display / hide 】

  • 2006.04
    -
    2011.03

    東京都済生会中央病院　

  • 2011.04
    -
    2014.03

    国立がん研究センター中央病院, 外科系レジデント

  • 2014.04
    -
    2016.03

    国立がん研究センター中央病院, 呼吸器外科, がん専門修練医

  • 2014.04
    -
    2025.03

    慶應義塾大学医学部外科学（呼吸器）, 呼吸器外科, 助教

  • 2025.04
    -
    Present

    慶應義塾大学医学部外科学（呼吸器）, 呼吸器外科, 専任講師

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Academic Degrees 【 Display / hide 】

  • 博士（医学）, Keio University, Dissertation, 2022.02

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Research Areas 【 Display / hide 】

  • Life Science / General surgery and pediatric surgery (胸郭変形疾患、漏斗胸)

  • Life Science / Respiratory surgery (胸部外科全般)

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Papers 【 Display / hide 】

  • Real-World Outcomes of Limited Resection for Tumours Greater Than 20mm in Non-Small Cell Lung Cancer

    Suzuki S., Asakura K., Masai K., Kaseda K., Hishida T., Kazama A., Shigenobu T., Hanawa R., Emoto K., Sato Y.

    European Journal of Cardio Thoracic Surgery 67 ( 10 )  2025.10

    ISSN  10107940

    　View Summary

    Sublobar resection is an established surgical option for early-stage non-small cell lung cancer. However, evidence remains limited regarding its use for tumours >20 mm in real-world settings. We evaluated characteristics and outcomes of limited resection in this context and identified predictors of local recurrence. We retrospectively analysed 165 patients with clinical stage I non-small cell lung cancer with tumours >20 mm who underwent limited resection between 2007 and 2017. Clinical, pathological, and radiological data were reviewed. The primary end-point was local recurrence, assessed using competing risk analysis. Overall survival and disease-free survival were estimated using Kaplan-Meier and Cox models. We analysed 165 patients with 13 local recurrence events. Among them, 146 (88.5%) had identifiable reasons for not undergoing lobectomy. Segmentectomy and wedge resection were performed in 59% and 41% of cases, respectively. Lymph node dissection was performed in all segmentectomies and in 20% of wedge resections. The 5-year overall and disease-free survival rates were 64.0% and 62.1%. Local recurrence occurred in 8%, more frequently after wedge resection than segmentectomy (13% vs 4%, P = .04). Solidpredominant tumours with a consolidation-to-tumour ratio greater than 0.5 accounted for 76% and were independently associated with lower disease-free survival (hazard ratio, 2.65; P = .05) and higher local recurrence (hazard ratio: infinite; P < .001). No local recurrence was observed in tumours with a ground-glass opacity-predominant pattern. Limited resection showed acceptable outcomes in lung cancers >20 mm, especially with ground-glass opacity; solidpredominant CT patterns were strongly linked to recurrence.

  • Lineage-specific transcription factor landscape of thymic neuroendocrine tumors

    Omura S., Kurebayashi Y., Hamamoto J., Terai H., Imoto T., Suzuki M., Nakagawa K., Suzuki T., Shigenobu T., Yoshizu A., Maeda C., Kaji M., Okubo Y., Suzuki S., Masai K., Kaseda K., Fukunaga K., Yasuda H., Asakura K.

    Lung Cancer 208 2025.10

    ISSN  01695002

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    Introduction: Thymic neuroendocrine tumors (TNETs) are rare malignancies characterized by aggressive clinical behavior and limited therapeutic options. In small cell lung cancer (SCLC), molecular subtypes based on the expression of lineage-defining transcription factors (TFs)—ASCL1, NEUROD1, POU2F3, and YAP1—have been proposed. However, the TF landscape of TNETs remains poorly defined. Given the pathological similarities among neuroendocrine tumors across organs, we aimed to investigate whether the TF-based classification system used in SCLC is applicable to TNETs. Methods: Sixteen pathologically confirmed TNETs—including large cell neuroendocrine carcinoma (LCNEC), thymic small cell carcinoma (TSCC), atypical carcinoid (AC), and typical carcinoid (TC)—were retrospectively analyzed. Immunohistochemistry was performed to evaluate classical neuroendocrine (NE) markers (synaptophysin, chromogranin A, CD56) and TFs (ASCL1, NEUROD1, POU2F3, YAP1). H-scores were calculated, and tumors were categorized according to TFs expression profiles. Results: Synaptophysin was strongly expressed in all cases, while chromogranin A and CD56 showed variable expression, with reduced levels in LCNEC and TSCC. The combined NE score was significantly higher in carcinoid tumors compared to LCNEC and TSCC. For TFs, ASCL1 expression was observed in 93.8 % of cases, whereas NEUROD1 and POU2F3 were rarely or not expressed. YAP1 expression was confined to LCNEC cases, all of which co-expressed ASCL1 and YAP1. Based on H-scores, TNETs were classified into three subgroups: (1) ASCL1-positive/YAP1-negative (n = 12, 75 %), (2) ASCL1/YAP1 double-positive (n = 3, 19 %), and (3) double-negative (n = 1, 6 %). Conclusion: This study reveals molecular heterogeneity among TNETs. Notably, ASCL1 and YAP1 co-expression characterizes all LCNEC cases, making a distinct TF landscape in high-grade TNETs.

  • Survival impact of pathologic features after salvage lung resection following definitive chemoradiotherapy or systemic therapy for initially unresectable lung cancer

    Oka N., Hishida T., Kaseda K., Suzuki Y., Okubo Y., Masai K., Asakura K., Emoto K., Asamura H.

    General Thoracic and Cardiovascular Surgery 73 ( 5 ) 362 - 371 2025.05

    ISSN  18636705

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    Purpose: Salvage surgery for primary lung cancer is expected to become increasingly common. This study aimed to clarify the survival impact of pathologic characteristics after salvage surgery. Methods: Consecutive patients who underwent salvage surgery following definitive chemoradiotherapy or systemic therapy for initially unresectable lung cancer from 2010 to 2020 were enrolled in this study. The tumor slides were reviewed to determine the size of the tumor bed and the proportions of viable tumor, necrosis, and stroma. Results: A total of 23 patients were evaluated, and 18 had clinical stage IIIB–IV disease. Six received chemoradiotherapy and 17 received systemic therapy alone. A major pathologic response (MPR, ≤ 10% of viable tumor) was observed in 6 patients, and 4 patients achieved a pathological complete response. The 3-year overall and recurrence-free survival rates (OS and RFS) were 78.6% and 59.2%, respectively. There was no significant difference in OS between patients with and without MPR, and even non-MPR patients achieved a favorable 3-year OS of 70.2%. Meanwhile, patients with high (≥ 30%) stroma showed significantly better OS than those with low (< 30%) stroma (3-year OS: 100% vs. 23.3%, p < 0.001). Conclusions: This study showed that the proportion of stroma can be useful for predicting long-term survival after salvage surgery. Further large-scale studies are warranted to confirm the current findings.

  • Initial single-institutional experience with salvage surgery for stage IV non-small-cell lung cancer

    Hishida T., Oka N., Yano K., Omura S., Okubo Y., Masai K., Kaseda K., Ohgino K., Terai H., Yasuda H., Asakura K.

    Interdisciplinary Cardiovascular and Thoracic Surgery 40 ( 3 )  2025.03

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    The purpose of this study was to assess surgical outcomes of salvage surgery for clinical stage IV non-small-cell lung cancer. A total of 14 patients who underwent lung resection following systemic therapy between 2010 and 2022 were included in this study. Systemic therapy prior to surgery included agents including epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) in eight patients and non-TKI agents in six (chemotherapy alone: four, chemotherapy plus immune checkpoint inhibitors: two). During a median follow-up of 5.2 years, the EGFR-TKI group showed a favourable 5-year overall survival of 83%; however, it was due to treatment after relapse, and there were no 4-year relapse-free survivors. The non-EGFR-TKI group showed a 5-year relapse-free survival of 33%, and 2 patients have survived more than 3 years without any relapse and further treatment. When considering the role of surgery in multimodal treatment for initial c-stage IV non-small-cell lung cancer, salvage surgery following non-TKI therapy (chemotherapy with or without immune checkpoint inhibitor) can be regarded as genuine salvage surgery.

  • Thoracic posture-related morphological changes in patients with pectus excavatum versus healthy controls

    Suzuki T., Asakura K., Yamada Y., Masai K., Yamada M., Yokoyama Y., Okubo Y., Kaseda K., Hishida T., Jinzaki M.

    European Journal of Cardio Thoracic Surgery 66 ( 5 )  2024.11

    ISSN  10107940

    　View Summary

    OBJECTIVES. Cases of severe pectus excavatum presenting with worsening cardiopulmonary symptoms in the upright position have been reported. However, the underlying mechanism remains unclear. We evaluated posture-related morphological changes of the thorax in patients with pectus excavatum. METHODS. Chest morphology was evaluated preoperatively using upright and supine computed tomography in 21 patients with pectus excavatum and 35 healthy volunteers. The minimum anterior–posterior thoracic diameter, depression depth, and Haller index on horizontal sections, as well as the T6-12 plumb line distance on sagittal sections, were compared between the 2 positions. RESULTS. In patients with pectus excavatum (median age, 22 years; 18 males and 3 females), the minimum anterior–posterior diameter was smaller (4.5 vs 5.1 cm, P < 0.001) and the Haller index was greater (10.1 vs 6.4, P < 0.001) in the upright position than in the supine position. The T6-T12 plumb line distance was longer in the upright position (2.4 vs 0.8 cm, P < 0.001), while the depression depth showed no significant difference. Healthy volunteers exhibited similar changes. The degree of spinal curvature increased in the upright position due to the anterior shift of the lower thoracic vertebrae, resulting in a shorter anterior–posterior diameter, irrespective of chest wall deformity. One patient with dyspnoea only in the upright position exhibited compression of the right inferior pulmonary vein only on upright computed tomography. CONCLUSIONS. The minimum anterior–posterior diameter is shorter in the upright position. This may explain the worsening of cardiopulmonary symptoms in patients with severe pectus excavatum when in an upright position.

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

  • Development of a new respiratory function index for treating pectus excavatum using computational fluid dynamics and the creation of a surgical support system.

    2025.04
    -
    2028.03

    基盤研究(C), Principal investigator

  • 画像データ解析に基づく漏斗胸形態分類の構築と新規手術支援システムの開発

    2021.04
    -
    2024.03

    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Principal investigator

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Courses Taught 【 Display / hide 】

  • LECTURE SERIES, SURGERY

    2025

  • LECTURE SERIES, SURGERY

    2024

  • LECTURE SERIES, SURGERY

    2023

  • LECTURE SERIES, SURGERY

    2022

  • LECTURE SERIES, SURGERY

    2021

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