A rare presentation of malignant mesothelioma of the tunica vaginalis managed with immunotherapy and review of the literature.

Key Clinical Message: We describe the first case in literature of malignant mesothelioma of the tunica vaginalis that has shown partial response to systemic immunotherapy (ipilimumab-nivolumab) post orchiectomy, warranting further investigation in a trial setting. Abstract: We present a case report of an 80-year-old ex-smoker with a rare diagnosis of metastatic mesothelioma of the tunica vaginalis, managed with immunotherapy. The patient, with no known history of asbestos exposure, presented with a left scrotal mass and pain. Scrotal ultrasound confirmed a large paratesticular mass, and computed tomography (CT) of the chest, abdomen, and pelvis revealed a bilobed mass in the left scrotal compartment without associated inguinal or abdominopelvic lymphadenopathy, and an indeterminate, subcentimeter, bi-basal subpleural nodules. He underwent a left orchiectomy, and histopathology confirmed the diagnosis of a paratesticular mesothelioma. Postoperatively, the patient had a positron emission tomography (PET) scan showing a new right pleural effusion as well as increasing size of the lobar and pleural nodules bilaterally, all metabolically active and suggestive of progressive metastatic disease. The patient was commenced on ipilimumab and nivolumab immunotherapy, a regimen indicated for malignant pleural mesothelioma; however, the efficacy on paratesticular mesothelioma is not known. After 6 months of treatment, the patient demonstrated a partial response to immunotherapy, with a reduction in the size of known pleural nodules and effusion.Literature review suggests that diagnosis requires a high index of suspicion and patients commonly have metastatic disease at the time of diagnosis. Orchiectomy is a common management modality. However, the role, regimen, and benefits of systemic therapy are unclear, warranting further studies investigating management strategies.