Patient with recurrent paratesticular malignant mesothelioma and multiple primary neoplasms

Paratesticular malignant mesothelioma (MM) is a rare tumor frequently associated with asbestos exposure. Therefore, we present an even rarer case of a 78-year-old male patient diagnosed with multiple primary neoplasms, including prostate cancer, lung cancer, paratesticular MM, and upper tract urothelial carcinoma. The patient initially presented with a painless testicular mass and had a notable medical history of prostate and lung cancers. Following physical examination and an ultrasound evaluation, he underwent radical right inguinal orchiectomy, which revealed paratesticular MM. The patient's lung cancer recurrence and subsequent treatment coincided with periods of no MM recurrence. However, after the lung cancer treatment, the MM recurred multiple times within short intervals. This unique case indicates that systemic treatments for lung cancer, specifically cisplatin-based chemotherapy and atezolizumab immunotherapy, might also have an anti-tumor effect on paratesticular MM. Although MM combined with multiple primary neoplasms is challenging to treat and frequently recurs, treatments for other malignancies, as evidenced in this case, may have suppressive effects on the recurrence and metastasis of MM.