Efficacy of Nivolumab in Chemotherapy-Resistant Mesothelioma of the Tunica Vaginalis Testis: A Case Report

Our plain-English summary of Efficacy of Nivolumab in Chemotherapy-Resistant Mesothelioma of the Tunica Vaginalis Testis: A Case Report, by H. Koyanagi, T. Kawahara, N. Inagawa, et al (Cancer Reports, 2026).

The study

• Authors: H. Koyanagi, T. Kawahara, N. Inagawa, M. Shiga, H. Sakurai, A. Yamaguchi, K. Tanuma, S. Nitta, K. Kojo, M. Shiga, Y. Nagumo, A. Ikeda, S. Kandori, A. Hoshi, H. Negoro, H. Kawai, D. Matsubara, H. Nishiyama
• Journal: Cancer Reports
• Published: 2026;9(8):e70647
• Type of article: Case report
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Mesothelioma of the tunica vaginalis testis is a rare neoplasm, accounting for less than 1% of all mesothelioma cases. Due to the rarity of this disease, a standard treatment has not been established. Clinical management is generally adapted from the strategies used for pleural mesothelioma. Although immune checkpoint inhibitors (ICIs) have demonstrated efficacy in treating pleural mesothelioma, their role in mesothelioma of the tunica vaginalis testis remains uncharacterized due to a lack of evidence. This is the first report documenting a clinical response to nivolumab in chemoresistant mesothelioma of the tunica vaginalis testis.

Case: A 71-year-old man presented with painless left scrotal swelling and was initially diagnosed with a hydrocele at the referring hospital. One year later, hydrocelectomy revealed partial thickening of the tunica without malignancy. A subsequent magnetic resonance imaging analysis revealed a new intratesticular nodule. Orchiectomy was performed, and the pathological findings revealed an epithelioid mesothelioma. He was referred to Tsukuba University Hospital for further treatment. He also had a history of Self-Defense Force service, which suggested possible asbestos exposure. Imaging revealed pelvic lymphadenopathy with fluorodeoxyglucose uptake in the right external iliac lymph nodes. He received four cycles of cisplatin and pemetrexed every 3 weeks, resulting in stable disease. Bilateral pelvic lymph node dissection was performed and confirmed the presence of metastatic mesothelioma. Nine months after the surgery, bilateral inguinal lymph node recurrence occurred, and he received cisplatin monotherapy because of renal impairment. Despite four additional cycles of cisplatin monotherapy, the disease progressed. Therefore, chemotherapy was discontinued, and nivolumab was administered. Nivolumab resulted in sustained tumor shrinkage. However, after 3 months of treatment, he developed immune-related encephalitis requiring corticosteroid therapy and nivolumab discontinuation. After 16 months of nivolumab initiation, he was dead from the disease.

Conclusion: This is the first report documenting the clinical response of a chemoresistant mesothelioma of the tunica vaginalis testis to nivolumab. ICIs are a promising treatment option for this rare and challenging disease.

© 2026 The Author(s). Cancer Reports published by Wiley Periodicals LLC.

In plain English

This case report described one man in Japan with epithelioid mesothelioma of the tunica vaginalis testis, the lining around the testis. The article gives his age as 71 at presentation, though its table lists 78. Painless left scrotal swelling was first diagnosed as a hydrocele, and the tumor was found after removal of the testis. The authors wrote that his Self-Defense Force service suggested possible asbestos exposure. No fiber type or amount was reported. The cancer spread to pelvic lymph nodes. Four cycles of cisplatin and pemetrexed gave stable disease, and the nodes were removed. Nine months later it returned in the groin lymph nodes and progressed despite cisplatin alone. The tumors then shrank on nivolumab, an immunotherapy drug. After 3 months he developed immune-related encephalitis (brain inflammation), so nivolumab was stopped and not restarted. He died of the disease 16 months after starting nivolumab. The authors concluded this was the first reported response of this kind and that these drugs are a promising option. They added that serious side effects need watching and more studies are needed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: case report (one patient)
• Who was studied: One man with epithelioid mesothelioma of the tunica vaginalis testis, referred to Tsukuba University Hospital, Japan; age given as 71 at presentation in the abstract, 78 in Table 1; died November 2025
• Exposure: Possible asbestos exposure suggested by past Self-Defense Force service; no fiber type, product or dose reported. Treatments: cisplatin plus pemetrexed, cisplatin alone, then nivolumab
• Main results:
  • Four cycles of cisplatin and pemetrexed every 3 weeks resulted in stable disease
  • Pelvic lymph node removal on both sides confirmed metastatic mesothelioma
  • Nine months after surgery the cancer recurred in the groin (inguinal) lymph nodes on both sides; cisplatin alone was given because of kidney impairment, and the disease progressed after four more cycles
  • After chemotherapy was stopped, nivolumab produced sustained tumor shrinkage
  • After 3 months of nivolumab, the patient developed immune-related encephalitis needing corticosteroids, and nivolumab was stopped
  • Restarting nivolumab was considered but withheld after consulting neurologists because of the perceived high risk of recurrent encephalitis
  • The patient died of the disease 16 months after starting nivolumab
  • Tumor tissue stained positive for calretinin and CK5/6, consistent with mesothelioma
• The authors' conclusion: The authors concluded that this is the first report of a chemotherapy-resistant mesothelioma of the tunica vaginalis testis responding to nivolumab. They called immune checkpoint inhibitors a promising option for this rare disease, while warning that clinicians must watch for severe immune-related side effects.
• Limitations the authors state:
  • The authors noted that the existing literature has shown no definitive benefit of this treatment
  • The authors stated that further studies and case reports are needed to establish the efficacy and safety of these drugs in this disease

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Nivolumab (Opdivo), Chemotherapy, Mesothelioma, Tunica Vaginalis, Neoplasm, Pleural Mesothelioma, checkpoint inhibitors, Hydrocele.

Related studies

• Mesothelioma of the tunica vaginalis testis — K.J. Butnor, E.N. Pavlisko, et al. (2019)
• Mesothelioma of the tunica vaginalis testis: report of 2 cases with asbestos occupational exposure — G. Gorini, M. Pinelli, et al. (2005)
• Nivolumab versus placebo in patients with relapsed malignant mesothelioma (CONFIRM): a multicentre, double-blind, randomised, phase 3 trial — D.A. Fennell, S. Ewings, et al. (2021)
• Constitutive inflammation and epithelial-mesenchymal transition dictate sensitivity to nivolumab in CONFIRM: a placebo-controlled, randomised phase III trial — D.A. Fennell, K. Hill, et al. (2025)
• Pseudo-hyperprogression of Malignant Pleural Mesothelioma Treated with Nivolumab — M. Yanai, T. Sakamoto, et al. (2025)
• Malignant mesothelioma of the tunica vaginalis testis: diagnostic studies and differential diagnosis — S.S. Chekol, C.C. Sun (2012)

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