Abstract Malignant pleural mesothelioma is a rare, aggressive tumor arising from mesothelial cells lining the pleural cavities. Although asbestos exposure accounts for approximately 95% of cases, a small subset occurs in patients without an identifiable exposure and may be associated with ionizing radiation or genetic mutations, such as BRCA. Herein, we present a case of malignant pleural mesothelioma developing one year after pelvic radiation therapy for anal cancer in a patient without known asbestos exposure. An 82-year-old male with a history of anal squamous cell carcinoma treated with chemotherapy and radiation approximately one year prior presented with progressive dyspnea and intermittent fevers over 3-4 months. An outpatient chest CT had revealed bilateral pleural effusions. He underwent two thoracenteses in the outpatient setting, each with 1500 mL of exudative, serosanguinous fluid aspirated with cytology showing mesothelial cells but no evidence of malignancy. On admission, CT imaging revealed a partially loculated left-sided pleural effusion. With concern for superimposed pneumonia, he was initiated on empiric ceftriaxone and vancomycin. Due to the recurrence of the left-sided pleural effusion, he underwent left-sided thoracotomy with pleural biopsy, which confirmed epithelioid malignant mesothelioma. Given his poor functional status, the patient was not a candidate for chemotherapy or surgery. He was initiated on nivolumab every four weeks with consideration of pleurodesis for symptom control of recurrent effusions. Malignant mesothelioma without previous asbestos exposure is rare, making up only 5-10% of reported cases, with prior radiation therapy recognized as a potential risk factor. This case illustrates an unusual presentation of mesothelioma developing approximately one year after pelvic radiation therapy. Of note, the malignancy arose outside the field of radiation within a very short latency period, highlighting the potential for secondary mesothelioma to develop even after non-thoracic irradiation. This case additionally demonstrates the diagnostic challenges of malignant mesothelioma. Despite repeated large-volume thoracenteses, this patient’s cytology testing remained nondiagnostic, emphasizing the importance of tissue biopsy in recurrent, unexplained exudative effusions. Although the epithelioid subtype generally carries a more favorable prognosis, malignant mesothelioma remains an aggressive disease with a median survival of one year. Early recognition and diagnosis are paramount to optimize treatment and improve patient outcomes. This abstract is funded by: None
Jamal et al. (Fri,) studied this question.